1.
Aqueous humour
–
The aqueous humour is a transparent, watery fluid similar to plasma, but containing low protein concentrations. It is secreted from the epithelium, a structure supporting the lens. Amino acids, transported by ciliary muscles 98% water Electrolytes Ascorbic acid Glutathione Immunoglobulins Maintains the intraocular pressure and it is this hydrostatic pressure which keeps the eyeball in a roughly spherical shape and keeps the walls of the eyeball taut. Provides nutrition for the avascular ocular tissues, posterior cornea, trabecular meshwork, lens, may serve to transport ascorbate in the anterior segment to act as an antioxidant agent. Presence of immunoglobulins indicate a role in response to defend against pathogens. Provides inflation for expansion of the cornea and thus increased protection against dust, wind, pollen grains, the main eye structures related to aqueous humor dynamics are the ciliary body, and the trabecular meshwork and the uveoscleral pathway. Aqueous humor is secreted into the chamber by the ciliary body. 5 alpha-dihydrocortisol, an enzyme inhibited by 5-alpha reductase inhibitors, may be involved in production of aqueous humor, aqueous humor is continually produced by the ciliary processes and this rate of production must be balanced by an equal rate of aqueous humor drainage. Small variations in the production or outflow of aqueous humour will have an influence on the intraocular pressure. From there, the aqueous humour exits the eye through the trabecular meshwork into Schlemms canal It flows through 25–30 collector canals into the episcleral veins, the greatest resistance to aqueous flow is provided by the trabecular meshwork, and this is where most of the aqueous outflow occurs. The internal wall of the canal is very delicate and allows the fluid to filter due to pressure of the fluid within the eye. The secondary route is the drainage, and is independent of the intraocular pressure, the aqueous flows through here. The fluid is normally 15 mmHg above atmospheric pressure, so when a syringe is injected the fluid flows easily, if the fluid is leaking, due to collapse and wilting of cornea, the hardness of the normal eye is therefore corroborated. Glaucoma is a progressive optic neuropathy where retinal ganglion cells and their axons die causing a corresponding visual field defect, an important risk factor is increased intraocular pressure either through increased production or decreased outflow of aqueous humour. Increased resistance to outflow of aqueous humour may occur due to an abnormal trabecular mesh work or to obliteration of the due to injury or disease of the iris. However, increased pressure is neither sufficient nor necessary for development of primary open angle glaucoma. Uncontrolled glaucoma typically leads to visual field loss and ultimately blindness, archived from the original on 2014-01-01
2.
Solvation shell
–
A solvation shell is the solvent interface of any chemical compound or biomolecule that constitutes the solute. When the solvent is water it is referred to as a hydration shell or hydration sphere. A classic example is when water molecules arrange around a metal ion, for example, if the latter were a cation, the electronegative oxygen atom of the water molecule would be attracted electrostatically to the positive charge on the metal ion. The result is a shell of water molecules that surround the ion. This shell can be several thick, dependent upon the charge of the ion, its distribution. The hydration shell that forms around proteins is of importance in biochemistry. This interaction of the surface with the surrounding water is often referred to as protein hydration and is fundamental to the activity of the protein. The hydration layer around a protein has found to have dynamics distinct from the bulk water to a distance of 1 nm. With other solvents and solutes, varying steric and kinetic factors can affect the solvation shell. They result from an incomplete clustering of side-chain nonpolar groups that wrap the polar pair within the protein structure, dehydrons promote the removal of surrounding water through protein associations or ligand binding. Dehydrons can be identified by calculating the reversible work per unit area required to span the aqueous interface of a soluble protein, metal ions in aqueous solution Water model Poisson-Boltzmann equation Hydration energy Solvation London South Bank University pages on protein hydration Journal of Chemical Physics Book
3.
Solution
–
In chemistry, a solution is a homogeneous mixture composed of two or more substances. In such a mixture, a solute is a substance dissolved in another substance, the mixing process of a solution happens at a scale where the effects of chemical polarity are involved, resulting in interactions that are specific to solvation. The solution assumes the characteristics of the solvent when the solvent is the fraction of the mixture. The concentration of a solute in a solution is the mass of that solute expressed as a percentage of the mass of the whole solution, a solution is a homogeneous mixture of two or more substances. The particles of solute in a solution cannot be seen by the naked eye, a solution does not allow beams of light to scatter. The solute from a solution cannot be separated by filtration and it is composed of only one phase. Homogeneous means that the components of the form a single phase. Heterogeneous means that the components of the mixture are of different phase, the properties of the mixture can be uniformly distributed through the volume but only in absence of diffusion phenomena or after their completion. Usually, the present in the greatest amount is considered the solvent. Solvents can be gases, liquids or solids, one or more components present in the solution other than the solvent are called solutes. The solution has the physical state as the solvent. If the solvent is a gas, only gases are dissolved under a set of conditions. An example of a solution is air. Since interactions between molecules play almost no role, dilute gases form rather trivial solutions, in part of the literature, they are not even classified as solutions, but addressed as mixtures. If the solvent is a liquid, then almost all gases, liquids, here are some examples, Gas in liquid, Oxygen in water Carbon dioxide in water – a less simple example, because the solution is accompanied by a chemical reaction. Liquid in liquid, The mixing of two or more substances of the same chemistry but different concentrations to form a constant, alcoholic beverages are basically solutions of ethanol in water. Solid in liquid, Sucrose in water Sodium chloride or any other salt in water, solutions in water are especially common. Counterexamples are provided by liquid mixtures that are not homogeneous, colloids, body fluids are examples for complex liquid solutions, containing many solutes
4.
Water
–
Water is a transparent and nearly colorless chemical substance that is the main constituent of Earths streams, lakes, and oceans, and the fluids of most living organisms. Its chemical formula is H2O, meaning that its molecule contains one oxygen, Water strictly refers to the liquid state of that substance, that prevails at standard ambient temperature and pressure, but it often refers also to its solid state or its gaseous state. It also occurs in nature as snow, glaciers, ice packs and icebergs, clouds, fog, dew, aquifers, Water covers 71% of the Earths surface. It is vital for all forms of life. Only 2. 5% of this water is freshwater, and 98. 8% of that water is in ice and groundwater. Less than 0. 3% of all freshwater is in rivers, lakes, and the atmosphere, a greater quantity of water is found in the earths interior. Water on Earth moves continually through the cycle of evaporation and transpiration, condensation, precipitation. Evaporation and transpiration contribute to the precipitation over land, large amounts of water are also chemically combined or adsorbed in hydrated minerals. Safe drinking water is essential to humans and other even though it provides no calories or organic nutrients. There is a correlation between access to safe water and gross domestic product per capita. However, some observers have estimated that by 2025 more than half of the population will be facing water-based vulnerability. A report, issued in November 2009, suggests that by 2030, in developing regions of the world. Water plays an important role in the world economy, approximately 70% of the freshwater used by humans goes to agriculture. Fishing in salt and fresh water bodies is a source of food for many parts of the world. Much of long-distance trade of commodities and manufactured products is transported by boats through seas, rivers, lakes, large quantities of water, ice, and steam are used for cooling and heating, in industry and homes. Water is an excellent solvent for a variety of chemical substances, as such it is widely used in industrial processes. Water is also central to many sports and other forms of entertainment, such as swimming, pleasure boating, boat racing, surfing, sport fishing, Water is a liquid at the temperatures and pressures that are most adequate for life. Specifically, at atmospheric pressure of 1 bar, water is a liquid between the temperatures of 273.15 K and 373.15 K
5.
Chemical equation
–
The coefficients next to the symbols and formulae of entities are the absolute values of the stoichiometric numbers. The first chemical equation was diagrammed by Jean Beguin in 1615, a chemical equation consists of the chemical formulas of the reactants and the chemical formula of the products. The two are separated by a symbol and each individual substances chemical formula is separated from others by a plus sign. But, for equations involving complex chemicals, rather than reading the letter and its subscript, using IUPAC nomenclature, this equation would be read as hydrochloric acid plus sodium yields sodium chloride and hydrogen gas. This equation indicates that sodium and HCl react to form NaCl, the stoichiometric coefficients result from the law of conservation of mass and the law of conservation of charge. Symbols are used to differentiate different types of reactions. To denote the type of reaction, = symbol is used to denote a stoichiometric relation, → symbol is used to denote a net forward reaction. ⇄ symbol is used to denote a reaction in both directions, ⇌ symbol is used to denote an equilibrium. The physical state of chemicals is very commonly stated in parentheses after the chemical symbol. When stating physical state, denotes a solid, denotes a liquid, denotes a gas, if the reaction requires energy, it is indicated above the arrow. A capital Greek letter delta is put on the arrow to show that energy in the form of heat is added to the reaction. H ν is used if the energy is added in the form of light, other symbols are used for other specific types of energy or radiation. The law of conservation of mass dictates that the quantity of each element does not change in a chemical reaction, thus, each side of the chemical equation must represent the same quantity of any particular element. Likewise, the charge is conserved in a chemical reaction, therefore, the same charge must be present on both sides of the balanced equation. One balances a chemical equation by changing the number for each chemical formula. Simple chemical equations can be balanced by inspection, that is, by trial, another technique involves solving a system of linear equations. Balanced equations are written with smallest whole-number coefficients, if there is no coefficient before a chemical formula, the coefficient 1 is understood. Looking at the atom, the right-hand side has two atoms, while the left-hand side has four
6.
Chemical formula
–
These are limited to a single typographic line of symbols, which may include subscripts and superscripts. A chemical formula is not a name, and it contains no words. Although a chemical formula may imply certain simple chemical structures, it is not the same as a full chemical structural formula. Chemical formulas can fully specify the structure of only the simplest of molecules and chemical substances, the simplest types of chemical formulas are called empirical formulas, which use letters and numbers indicating the numerical proportions of atoms of each type. Molecular formulas indicate the numbers of each type of atom in a molecule. For example, the formula for glucose is CH2O, while its molecular formula is C6H12O6. This is possible if the relevant bonding is easy to show in one dimension, an example is the condensed molecular/chemical formula for ethanol, which is CH3-CH2-OH or CH3CH2OH. For reasons of structural complexity, there is no condensed chemical formula that specifies glucose, chemical formulas may be used in chemical equations to describe chemical reactions and other chemical transformations, such as the dissolving of ionic compounds into solution. A chemical formula identifies each constituent element by its chemical symbol, in empirical formulas, these proportions begin with a key element and then assign numbers of atoms of the other elements in the compound, as ratios to the key element. For molecular compounds, these numbers can all be expressed as whole numbers. For example, the formula of ethanol may be written C2H6O because the molecules of ethanol all contain two carbon atoms, six hydrogen atoms, and one oxygen atom. Some types of compounds, however, cannot be written with entirely whole-number empirical formulas. An example is boron carbide, whose formula of CBn is a variable non-whole number ratio with n ranging from over 4 to more than 6.5. When the chemical compound of the consists of simple molecules. These types of formulas are known as molecular formulas and condensed formulas. A molecular formula enumerates the number of atoms to reflect those in the molecule, so that the formula for glucose is C6H12O6 rather than the glucose empirical formula. However, except for very simple substances, molecular chemical formulas lack needed structural information, for simple molecules, a condensed formula is a type of chemical formula that may fully imply a correct structural formula. For example, ethanol may be represented by the chemical formula CH3CH2OH
7.
Salt
–
Salt is present in vast quantities in seawater, where it is the main mineral constituent. The open ocean has about 35 grams of solids per litre, Salt is essential for life in general, and saltiness is one of the basic human tastes. The tissues of animals contain larger quantities of salt than do plant tissues, Salt is one of the oldest and most ubiquitous food seasonings, and salting is an important method of food preservation. Salt was also prized by the ancient Hebrews, the Greeks, the Romans, the Byzantines, the Hittites, Egyptians, and the Indians. Salt became an important article of trade and was transported by boat across the Mediterranean Sea, along specially built salt roads, the scarcity and universal need for salt has led nations to go to war over it and use it to raise tax revenues. Salt is used in ceremonies and has other cultural significance. Salt is processed from salt mines, or by the evaporation of seawater or mineral-rich spring water in shallow pools. Its major industrial products are caustic soda and chlorine, and is used in industrial processes including the manufacture of polyvinyl chloride, plastics, paper pulp. Of the annual production of around two hundred million tonnes of salt, only about 6% is used for human consumption. Other uses include water conditioning processes, de-icing highways, and agricultural use, edible salt is sold in forms such as sea salt and table salt which usually contains an anti-caking agent and may be iodised to prevent iodine deficiency. As well as its use in cooking and at the table, sodium is an essential nutrient for human health via its role as an electrolyte and osmotic solute. Excessive salt consumption can increase the risk of diseases, such as hypertension, in children. Such health effects of salt have long been studied, accordingly, numerous world health associations and experts in developed countries recommend reducing consumption of popular salty foods. The World Health Organization recommends that adults should consume less than 2,000 mg of sodium, humans have always tended to build communities either around sources of salt, or where they can trade for it. All through history the availability of salt has been pivotal to civilization, the word salary comes from the Latin word for salt because the Roman Legions were sometimes paid in salt. The Natron Valley was a key region that supported the Egyptian Empire to its north, because it supplied it with a kind of salt that came to be called by its name, natron. Even before this, what is now thought to have been the first city in Europe is Solnitsata, in Bulgaria, even the name Solnisata means salt works. A very ancient salt-works operation has been discovered at the Poiana Slatinei archaeological site next to a spring in Lunca, Neamț County
8.
Solvation
–
Solvation, also sometimes called dissolution, is the attraction and association of molecules of a solvent with molecules or ions of a solute. When a solute is soluble in a solvent, the solute’s molecules or ions will spread out. A molecule or ion of solute surrounded by solvent is known as a solvation complex, solvation is the process of reorganizing solvent and solute molecules into solvation complexes until the solute is distributed evenly within the solvent. Solvation depends on such as hydrogen bonding and van der Waals forces. Insoluble solutes prefer to maintain interactions among solute molecules rather than break apart, solvation of a solute by water is called hydration. By an IUPAC definition, solvation is an interaction of a solute with the solvent, in the solvated state, an ion in a solution is surrounded or complexed by solvent molecules. Solvated species can be described by number and the complex stability constants. The concept of the interaction can also be applied to an insoluble material, for example. Solvation is, in concept, distinct from solubility, solvation or dissolution is a kinetic process and is quantified by its rate. Solubility quantifies the dynamic equilibrium state achieved when the rate of dissolution equals the rate of precipitation, the consideration of the units makes the distinction clearer. The typical unit for dissolution rate is mol/s, the units for solubility express a concentration, mass per volume, molarity, etc. Solvation involves different types of interactions, hydrogen bonding, ion-dipole interactions. Which of these forces are at play depends on the structure and properties of the solvent. The similarity or complementary character of these properties between solvent and solute determines how well a solute can be solvated by a particular solvent, Solvent polarity is the most important factor in determining how well it solvates a particular solute. Polar solvents have molecular dipoles, meaning part of the solvent molecule has more electron density than another part of the molecule. The part with more electron density will experience a negative charge while the part with less electron density will experience a partial positive charge. Polar solvent molecules can solvate polar solutes and ions because they can orient the appropriate partially charged portion of the molecule towards the solute through electrostatic attraction and this stabilizes the system and creates a solvation shell around each particle of solute. Water is the most common and well-studied polar solvent, but others exist, such as ethanol, methanol, acetone, acetonitrile, polar solvents are often found to have a high dielectric constant, although other solvent scales are also used to classify solvent polarity
9.
Chemistry
–
Chemistry is a branch of physical science that studies the composition, structure, properties and change of matter. Chemistry is sometimes called the science because it bridges other natural sciences, including physics. For the differences between chemistry and physics see comparison of chemistry and physics, the history of chemistry can be traced to alchemy, which had been practiced for several millennia in various parts of the world. The word chemistry comes from alchemy, which referred to a set of practices that encompassed elements of chemistry, metallurgy, philosophy, astrology, astronomy, mysticism. An alchemist was called a chemist in popular speech, and later the suffix -ry was added to this to describe the art of the chemist as chemistry, the modern word alchemy in turn is derived from the Arabic word al-kīmīā. In origin, the term is borrowed from the Greek χημία or χημεία and this may have Egyptian origins since al-kīmīā is derived from the Greek χημία, which is in turn derived from the word Chemi or Kimi, which is the ancient name of Egypt in Egyptian. Alternately, al-kīmīā may derive from χημεία, meaning cast together, in retrospect, the definition of chemistry has changed over time, as new discoveries and theories add to the functionality of the science. The term chymistry, in the view of noted scientist Robert Boyle in 1661, in 1837, Jean-Baptiste Dumas considered the word chemistry to refer to the science concerned with the laws and effects of molecular forces. More recently, in 1998, Professor Raymond Chang broadened the definition of chemistry to mean the study of matter, early civilizations, such as the Egyptians Babylonians, Indians amassed practical knowledge concerning the arts of metallurgy, pottery and dyes, but didnt develop a systematic theory. Greek atomism dates back to 440 BC, arising in works by such as Democritus and Epicurus. In 50 BC, the Roman philosopher Lucretius expanded upon the theory in his book De rerum natura, unlike modern concepts of science, Greek atomism was purely philosophical in nature, with little concern for empirical observations and no concern for chemical experiments. Work, particularly the development of distillation, continued in the early Byzantine period with the most famous practitioner being the 4th century Greek-Egyptian Zosimos of Panopolis. He formulated Boyles law, rejected the four elements and proposed a mechanistic alternative of atoms. Before his work, though, many important discoveries had been made, the Scottish chemist Joseph Black and the Dutchman J. B. English scientist John Dalton proposed the theory of atoms, that all substances are composed of indivisible atoms of matter. Davy discovered nine new elements including the alkali metals by extracting them from their oxides with electric current, british William Prout first proposed ordering all the elements by their atomic weight as all atoms had a weight that was an exact multiple of the atomic weight of hydrogen. The inert gases, later called the noble gases were discovered by William Ramsay in collaboration with Lord Rayleigh at the end of the century, thereby filling in the basic structure of the table. Organic chemistry was developed by Justus von Liebig and others, following Friedrich Wöhlers synthesis of urea which proved that organisms were, in theory
10.
PH
–
In chemistry, pH is a numeric scale used to specify the acidity or basicity of an aqueous solution. It is approximately the negative of the base 10 logarithm of the concentration, measured in units of moles per liter. More precisely it is the negative of the logarithm to base 10 of the activity of the hydrogen ion, solutions with a pH less than 7 are acidic and solutions with a pH greater than 7 are basic. Pure water is neutral, at pH7, being neither an acid nor a base, contrary to popular belief, the pH value can be less than 0 or greater than 14 for very strong acids and bases respectively. The pH scale is traceable to a set of standard solutions whose pH is established by international agreement, the pH of aqueous solutions can be measured with a glass electrode and a pH meter, or an indicator. In the first papers, the notation had the H as a subscript to the p, as so. The exact meaning of the p in pH is disputed, but according to the Carlsberg Foundation and it has also been suggested that the p stands for the German Potenz, others refer to French puissance. Another suggestion is that the p stands for the Latin terms pondus hydrogenii, potentia hydrogenii and it is also suggested that Sørensen used the letters p and q simply to label the test solution and the reference solution. Currently in chemistry, the p stands for decimal cologarithm of, PH is defined as the decimal logarithm of the reciprocal of the hydrogen ion activity, aH+, in a solution. P H = − log 10 = log 10 For example and this definition was adopted because ion-selective electrodes, which are used to measure pH, respond to activity. For H+ number of electrons transferred is one and it follows that electrode potential is proportional to pH when pH is defined in terms of activity. The reference electrode may be a silver chloride electrode or a calomel electrode, the hydrogen-ion selective electrode is a standard hydrogen electrode. Reference electrode | concentrated solution of KCl || test solution | H2 | Pt Firstly, the cell is filled with a solution of hydrogen ion activity. Then the emf, EX, of the cell containing the solution of unknown pH is measured. PH = pH + E S − E X z The difference between the two measured emf values is proportional to pH and this method of calibration avoids the need to know the standard electrode potential. The proportionality constant, 1/z is ideally equal to 12.303 R T / F the Nernstian slope, to apply this process in practice, a glass electrode is used rather than the cumbersome hydrogen electrode. A combined glass electrode has a reference electrode. It is calibrated against buffer solutions of hydrogen ion activity
11.
Hydrophobic
–
In chemistry, hydrophobicity is the physical property of a molecule that is seemingly repelled from a mass of water. In contrast, hydrophiles are attracted to water, Hydrophobic molecules tend to be nonpolar and, thus, prefer other neutral molecules and nonpolar solvents. Because water molecules are polar, hydrophobes do not dissolve well among them, Hydrophobic molecules in water often cluster together, forming micelles. Water on hydrophobic surfaces will exhibit a high contact angle, examples of hydrophobic molecules include the alkanes, oils, fats, and greasy substances in general. Hydrophobic materials are used for oil removal from water, the management of oil spills, Hydrophobic is often used interchangeably with lipophilic, fat-loving. However, the two terms are not synonymous, while hydrophobic substances are usually lipophilic, there are exceptions—such as the silicones and fluorocarbons. The term hydrophobe comes from the Ancient Greek ὑδρόφοβος, having a horror of water, constructed from ὕδωρ, water, thus, the two immiscible phases will change so that their corresponding interfacial area will be minimal. This effect can be visualized in the phenomenon called phase separation, Superhydrophobic surfaces, such as the leaves of the lotus plant, are those that are extremely difficult to wet. The contact angles of a water droplet exceeds 150° and the angle is less than 10°. This is referred to as the Lotus effect, and is primarily a physical property related to interfacial tension, in 1805, Thomas Young defined the contact angle θ by analyzing the forces acting on a fluid droplet resting on a solid surface surrounded by a gas. Wenzels equation shows that microstructuring a surface amplifies the natural tendency of the surface, a hydrophobic surface becomes more hydrophobic when microstructured – its new contact angle becomes greater than the original. However, a hydrophilic surface becomes more hydrophilic when microstructured – its new contact angle less than the original. Liquid in the Cassie–Baxter state is more mobile than in the Wenzel state and we can predict whether the Wenzel or Cassie–Baxter state should exist by calculating the new contact angle with both equations. By a minimization of free energy argument, the relation that predicted the new contact angle is the state most likely to exist. Stated in mathematical terms, for the Cassie–Baxter state to exist, a new criterion for the switch between Wenzel and Cassie-Baxter states has been developed recently based on surface roughness and surface energy. Contact angle is a measure of static hydrophobicity, and contact angle hysteresis, contact angle hysteresis is a phenomenon that characterizes surface heterogeneity. When a pipette injects a liquid onto a solid, the liquid will form some contact angle, as the pipette injects more liquid, the droplet will increase in volume, the contact angle will increase, but its three-phase boundary will remain stationary until it suddenly advances outward. The contact angle the droplet had immediately before advancing outward is termed the advancing contact angle, the receding contact angle is now measured by pumping the liquid back out of the droplet
12.
Acid
–
An acid is a molecule or ion capable of donating a hydron, or, alternatively, capable of forming a covalent bond with an electron pair. The first category of acids is the donors or Brønsted acids. In the special case of solutions, proton donors form the hydronium ion H3O+ and are known as Arrhenius acids. Brønsted and Lowry generalized the Arrhenius theory to include non-aqueous solvents, acids form aqueous solutions with a sour taste, can turn blue litmus red, and react with bases and certain metals to form salts. The word acid is derived from the Latin acidus/acēre meaning sour, an aqueous solution of an acid has a pH less than 7 and is colloquially also referred to as acid, while the strict definition refers only to the solute. A lower pH means a higher acidity, and thus a higher concentration of hydrogen ions in the solution. Chemicals or substances having the property of an acid are said to be acidic, common aqueous acids include hydrochloric acid, acetic acid, sulfuric acid, and citric acid. As these examples show, acids can be solutions or pure substances, strong acids and some concentrated weak acids are corrosive, but there are exceptions such as carboranes and boric acid. The second category of acids are Lewis acids, which form a covalent bond with an electron pair, however, hydrogen chloride, acetic acid, and most other Brønsted-Lowry acids cannot form a covalent bond with an electron pair and are therefore not Lewis acids. Conversely, many Lewis acids are not Arrhenius or Brønsted-Lowry acids, in modern terminology, an acid is implicitly a Brønsted acid and not a Lewis acid, since chemists almost always refer to a Lewis acid explicitly as a Lewis acid. Modern definitions are concerned with the chemical reactions common to all acids. Most acids encountered in life are aqueous solutions, or can be dissolved in water, so the Arrhenius. The Brønsted-Lowry definition is the most widely used definition, unless otherwise specified, hydronium ions are acids according to all three definitions. Interestingly, although alcohols and amines can be Brønsted-Lowry acids, they can function as Lewis bases due to the lone pairs of electrons on their oxygen and nitrogen atoms. The Swedish chemist Svante Arrhenius attributed the properties of acidity to hydrogen ions or protons in 1884, an Arrhenius acid is a substance that, when added to water, increases the concentration of H+ ions in the water. Thus, an Arrhenius acid can also be described as a substance that increases the concentration of ions when added to water. Examples include molecular substances such as HCl and acetic acid, an Arrhenius base, on the other hand, is a substance which increases the concentration of hydroxide ions when dissolved in water. Thus, an Arrhenius acid could also be said to be one that decreases hydroxide concentration, in an acidic solution, the concentration of hydronium ions is greater than 10−7 moles per liter
13.
Intermolecular force
–
Intermolecular forces are weak relative to intramolecular forces – the forces which hold a molecule together. For example, the covalent bond, involving sharing electron pairs between atoms, is stronger than the forces present between neighboring molecules. Both sets of forces are essential parts of force fields used in molecular mechanics. The investigation of intermolecular forces starts from macroscopic observations which indicate the existence and these observations include non-ideal-gas thermodynamic behavior reflected by virial coefficients, vapor pressure, viscosity, superficial tension, and absorption data. The first reference to the nature of microscopic forces is found in Alexis Clairauts work Theorie de la Figure de la Terre, other scientists who have contributed to the investigation of microscopic forces include, Laplace, Gauss, Maxwell and Boltzmann. The link to microscopic aspects is given by virial coefficients and Lennard-Jones potentials, dipole-dipole interactions are electrostatic interactions between permanent dipoles in molecules. These interactions tend to align the molecules to increase attraction, an example of a dipole-dipole interaction can be seen in hydrogen chloride, the positive end of a polar molecule will attract the negative end of the other molecule and influence its position. Polar molecules have a net attraction between them, examples of polar molecules include hydrogen chloride and chloroform. H δ + − Cl δ − ⋯ H δ + − Cl δ − Often molecules contain dipolar groups and this occurs if there is symmetry within the molecule that causes the dipoles to cancel each other out. This occurs in such as tetrachloromethane and carbon dioxide. The dipole-dipole interaction between two atoms is usually zero, since atoms rarely carry a permanent dipole. Ion-dipole and ion-induced dipole forces are similar to dipole-dipole and induced-dipole interactions but involve ions, ion-dipole and ion-induced dipole forces are stronger than dipole-dipole interactions because the charge of any ion is much greater than the charge of a dipole moment. Ion-dipole bonding is stronger than hydrogen bonding, an ion-dipole force consists of an ion and a polar molecule interacting. They align so that the positive and negative groups are next to one another, an ion-induced dipole force consists of an ion and a non-polar molecule interacting. Like a dipole-induced dipole force, the charge of the ion causes distortion of the cloud on the non-polar molecule. A hydrogen bond is the attraction between the pair of an electronegative atom and a hydrogen atom that is bonded to either nitrogen, oxygen. The hydrogen bond is described as a strong electrostatic dipole-dipole interaction. Intermolecular hydrogen bonding is responsible for the boiling point of water compared to the other group 16 hydrides
14.
Precipitation (chemistry)
–
Precipitation is the creation of a solid from a solution. When the reaction occurs in a solution, the solid formed is called the precipitate. The chemical that causes the solid to form is called the precipitant, without sufficient force of gravity to bring the solid particles together, the precipitate remains in suspension. After sedimentation, especially when using a centrifuge to press it into a compact mass, Precipitation can be used as a medium. The precipitate-free liquid remaining above the solid is called the supernate or supernatant, powders derived from precipitation have also historically been known as flowers. When the solid appears in the form of fibers which have been through chemical processing. Sometimes the formation of a precipitate indicates the occurrence of a chemical reaction, if silver nitrate solution is poured into a solution of sodium chloride, a chemical reaction occurs forming a white precipitate of silver chloride. When potassium iodide solution reacts with lead nitrate solution, a precipitate of lead iodide is formed. Precipitation may occur if the concentration of a compound exceeds its solubility, Precipitation may occur rapidly from a supersaturated solution. Precipitation in solids is routinely used to synthesize nanoclusters, an important stage of the precipitation process is the onset of nucleation. The creation of a solid particle includes the formation of an interface, which requires some energy based on the relative surface energy of the solid. If this energy is not available, and no suitable nucleation surface is available, Precipitation reactions can be used for making pigments, removing salts from water in water treatment, and in classical qualitative inorganic analysis. Precipitation is also useful to isolate the products of a reaction during workup, ideally, the product of the reaction is insoluble in the reaction solvent. Thus, it precipitates as it is formed, preferably forming pure crystals, an example of this would be the synthesis of porphyrins in refluxing propionic acid. Thereafter, the precipitate may easily be separated by filtration, decanting, an example would be the synthesis of chromic tetraphenylporphyrin chloride, water is added to the DMF reaction solution, and the product precipitates. Precipitation is also useful in purifying products, crude bmim-Cl is taken up in acetonitrile, and dropped into ethyl acetate, another important application of an antisolvent is in ethanol precipitation of DNA. In metallurgy, precipitation from a solution is also a useful way to strengthen alloys. An example of a reaction, Aqueous silver nitrate is added to a solution containing potassium chloride
15.
Electric current
–
An electric current is a flow of electric charge. In electric circuits this charge is carried by moving electrons in a wire. It can also be carried by ions in an electrolyte, or by both ions and electrons such as in an ionised gas. The SI unit for measuring a current is the ampere. Electric current is measured using a device called an ammeter, electric currents cause Joule heating, which creates light in incandescent light bulbs. They also create magnetic fields, which are used in motors, inductors and generators, the particles that carry the charge in an electric current are called charge carriers. In metals, one or more electrons from each atom are loosely bound to the atom and these conduction electrons are the charge carriers in metal conductors. The conventional symbol for current is I, which originates from the French phrase intensité de courant, current intensity is often referred to simply as current. The I symbol was used by André-Marie Ampère, after whom the unit of current is named, in formulating the eponymous Ampères force law. The notation travelled from France to Great Britain, where it became standard, in a conductive material, the moving charged particles which constitute the electric current are called charge carriers. In other materials, notably the semiconductors, the carriers can be positive or negative. Positive and negative charge carriers may even be present at the same time, a flow of positive charges gives the same electric current, and has the same effect in a circuit, as an equal flow of negative charges in the opposite direction. Since current can be the flow of positive or negative charges. The direction of current is arbitrarily defined as the same direction as positive charges flow. This is called the direction of current I. If the current flows in the direction, the variable I has a negative value. When analyzing electrical circuits, the direction of current through a specific circuit element is usually unknown. Consequently, the directions of currents are often assigned arbitrarily
16.
Electrolyte
–
An electrolyte is a substance that produces an electrically conducting solution when dissolved in a polar solvent, such as water. The dissolved electrolyte separates into cations and anions, which disperse uniformly through the solvent, electrically, such a solution is neutral. The movement of anions and cations in opposite directions within the solution amounts to a current and this includes most soluble salts, acids, and bases. Some gases, such as chloride, under conditions of high temperature or low pressure can also function as electrolytes. Electrolyte solutions can also result from the dissolution of some biological and synthetic polymers, termed polyelectrolytes, a substance that dissociates into ions in solution acquires the capacity to conduct electricity. Sodium, potassium, chloride, calcium, magnesium, and phosphate are examples of electrolytes, in medicine, electrolyte replacement is needed when a patient has prolonged vomiting or diarrhea, and as a response to strenuous athletic activity. Commercial electrolyte solutions are available, particularly for children and athletes. Electrolyte monitoring is important in the treatment of anorexia and bulimia, the word electrolyte derives from the Greek lytós, meaning able to be untied or loosened. Arrheniuss explanation was that in forming a solution, the salt dissociates into charged particles, faradays belief had been that ions were produced in the process of electrolysis. Arrhenius proposed that, even in the absence of an electric current and he thus proposed that chemical reactions in solution were reactions between ions. For example, carbon dioxide gas dissolves in water to produce a solution that contains hydronium, carbonate, molten salts can also be electrolytes as, for example, when sodium chloride is molten, the liquid conducts electricity. An electrolyte in a solution may be described as concentrated if it has a concentration of ions. If a high proportion of the solute dissociates to form ions, the electrolyte is strong, if most of the solute does not dissociate. The properties of electrolytes may be exploited using electrolysis to extract constituent elements, in physiology, the primary ions of electrolytes are sodium, potassium, calcium, magnesium, chloride, hydrogen phosphate, and hydrogen carbonate. The electric charge symbols of plus and minus indicate that the substance is ionic in nature and has a distribution of electrons. Sodium is the main electrolyte found in extracellular fluid and potassium is the main intracellular electrolyte, all known higher lifeforms require a subtle and complex electrolyte balance between the intracellular and extracellular environments. In particular, the maintenance of precise osmotic gradients of electrolytes is important, such gradients affect and regulate the hydration of the body as well as blood pH, and are critical for nerve and muscle function. Various mechanisms exist in living species that keep the concentrations of different electrolytes under tight control, both muscle tissue and neurons are considered electric tissues of the body
17.
Ionization
–
Ionization is the process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons to form ions, often in conjunction with other chemical changes. Ionization can result from the loss of an electron after collisions with particles, collisions with other atoms, molecules and ions. Heterolytic bond cleavage and heterolytic substitution reactions can result in the formation of ion pairs, ionization can occur through radioactive decay by the internal conversion process, in which an excited nucleus transfers its energy to one of the inner-shell electrons causing it to be ejected. Everyday examples of gas ionization are such as within a fluorescent lamp or other electrical discharge lamps and it is also used in radiation detectors such as the Geiger-Müller counter or the ionization chamber. The ionization process is used in a variety of equipment in fundamental science and in such as mass spectrometry. Negatively charged ions are produced when an electron collides with an atom and is subsequently trapped inside the electric potential barrier. The process is known as electron capture ionization, positively charged ions are produced by transferring a sufficient amount of energy to a bound electron in a collision with charged particles or with photons. The threshold amount of the energy is known as ionization potential. The study of such collisions is of importance with regard to the few-body problem. The Townsend discharge is an example of the creation of positive ions. It is a reaction involving electrons in a region with a sufficiently high electric field in a gaseous medium that can be ionized. Following an original event, due to such as ionizing radiation. If the electric field is strong enough, the free electron gains sufficient energy to liberate a further electron when it collides with another molecule. The two free electrons then travel towards the anode and gain sufficient energy from the field to cause impact ionization when the next collisions occur. This is effectively a chain reaction of electron generation, and is dependent on the free electrons gaining sufficient energy between collisions to sustain the avalanche, ionization efficiency is the ratio of the number of ions formed to the number of electrons or photons used. The trend in the energy of atoms is often used to demonstrate the periodic behavior of atoms with respect to the atomic number. This is a tool for establishing and understanding the ordering of electrons in atomic orbitals without going into the details of wave functions or the ionization process. An example is presented in figure 1, the periodic abrupt decrease in ionization potential after rare gas atoms, for instance, indicates the emergence of a new shell in alkali metals
18.
Sugar
–
Sugar is the generic name for sweet, soluble carbohydrates, many of which are used in food. There are various types of derived from different sources. Simple sugars are called monosaccharides and include glucose, fructose, the table sugar or granulated sugar most customarily used as food is sucrose, a disaccharide of glucose and fructose. Sugar is used in prepared foods and it is added to some foods, in the body, sucrose is hydrolysed into the simple sugars fructose and glucose. Other disaccharides include maltose from malted grain, and lactose from milk, longer chains of sugars are called oligosaccharides or polysaccharides. Some other chemical substances, such as glycerol may also have a sweet taste, low-calorie food substitutes for sugar, described as artificial sweeteners, include aspartame and sucralose, a chlorinated derivative of sucrose. Sugars are found in the tissues of most plants and are present in sufficient concentrations for efficient commercial extraction in sugarcane, the world production of sugar in 2011 was about 168 million tonnes. The average person consumes about 24 kilograms of sugar each year, equivalent to over 260 food calories per person, since the latter part of the twentieth century, it has been questioned whether a diet high in sugars, especially refined sugars, is good for human health. Sugar has been linked to obesity, and suspected of, or fully implicated as a cause in the occurrence of diabetes, cardiovascular disease, dementia, macular degeneration, the etymology reflects the spread of the commodity. The English word sugar ultimately originates from the Sanskrit शर्करा, via Arabic سكر as granular or candied sugar, the contemporary Italian word is zucchero, whereas the Spanish and Portuguese words, azúcar and açúcar, respectively, have kept a trace of the Arabic definite article. The Old French word is zuchre and the contemporary French, sucre, the earliest Greek word attested is σάκχαρις. The English word jaggery, a brown sugar made from date palm sap or sugarcane juice, has a similar etymological origin – Portuguese jagara from the Sanskrit शर्करा. Sugar has been produced in the Indian subcontinent since ancient times and it was not plentiful or cheap in early times and honey was more often used for sweetening in most parts of the world. Originally, people chewed raw sugarcane to extract its sweetness, sugarcane was a native of tropical South Asia and Southeast Asia. Different species seem to have originated from different locations with Saccharum barberi originating in India and S. edule, one of the earliest historical references to sugarcane is in Chinese manuscripts dating back to 8th century BC that state that the use of sugarcane originated in India. Sugar was found in Europe by the 1st century AD, but only as an imported medicine and it is a kind of honey found in cane, white as gum, and it crunches between the teeth. It comes in lumps the size of a hazelnut, sugar is used only for medical purposes. Sugar remained relatively unimportant until the Indians discovered methods of turning sugarcane juice into granulated crystals that were easier to store, crystallized sugar was discovered by the time of the Imperial Guptas, around the 5th century AD
19.
Urea
–
Urea, also known as carbamide, is an organic compound with the chemical formula CO2. This amide has two groups joined by a carbonyl functional group. Urea serves an important role in the metabolism of nitrogen-containing compounds by animals and is the main nitrogen-containing substance in the urine of mammals and it is a colorless, odorless solid, highly soluble in water, and practically non-toxic. Dissolved in water, it is neither acidic nor alkaline, the body uses it in many processes, most notably nitrogen excretion. The liver forms it by combining two molecules with a carbon dioxide molecule in the urea cycle. Urea is widely used in fertilizers as a source of nitrogen and is an important raw material for the chemical industry, Friedrich Wöhlers discovery in 1828 that urea can be produced from inorganic starting materials was an important conceptual milestone in chemistry. More than 90% of world production of urea is destined for use as a nitrogen-release fertilizer. Urea has the highest nitrogen content of all solid nitrogenous fertilizers in common use, therefore, it has the lowest transportation costs per unit of nitrogen nutrient. The standard crop-nutrient rating of urea is 46-0-0, many soil bacteria possess the enzyme urease, which catalyzes conversion of urea to ammonia or ammonium ion and bicarbonate ion. Thus urea fertilizers rapidly transform to the form in soils. Ammonium and nitrate are readily absorbed by plants, and are the dominant sources of nitrogen for plant growth, Urea is also used in many multi-component solid fertilizer formulations. Urea is highly soluble in water and is also very suitable for use in fertilizer solutions. For fertilizer use, granules are preferred over prills because of their particle size distribution. The most common impurity of synthetic urea is biuret, which impairs plant growth, Urea is usually spread at rates of between 40 and 300 kg/ha but rates vary. Smaller applications incur lower losses due to leaching, during summer, urea is often spread just before or during rain to minimize losses from volatilization. Because of the nitrogen concentration in urea, it is very important to achieve an even spread. The application equipment must be calibrated and properly used. Drilling must not occur on contact with or close to seed, Urea dissolves in water for application as a spray or through irrigation systems
20.
Glycerol
–
Glycerol /ˈɡlɪsərɒl/ is a simple polyol compound. It is a colorless, odorless, viscous liquid that is sweet-tasting, the glycerol backbone is found in all lipids known as triglycerides. It is widely used in the industry as a sweetener and humectant. Glycerol has three groups that are responsible for its solubility in water and its hygroscopic nature. Although achiral, glycerol is prochiral with respect to reactions of one of the two primary alcohols, thus, in substituted derivatives, the stereospecific numbering labels each carbon as either sn-1, sn-2, or sn-3. Glycerol is generally obtained from plant and animal sources where it occurs as triglycerides, triglycerides are esters of glycerol with long-chain carboxylic acids. Approximately 950,000 tons per year are produced in the United States and it was projected in 2006 that by the year 2020, production would be six times more than demand. Glycerol from triglycerides is produced on a scale, but the crude product is of variable quality. It can be purified, but the process is expensive, some glycerol is burned for energy, but its heat value is low. High purity glycerol is obtained by distillation, vacuum is helpful due to the high boiling point of glycerol. Although usually not cost-effective, glycerol can be produced by various routes from propylene and this epichlorohydrin is then hydrolyzed to give glycerol. Chlorine-free processes from propylene include the synthesis of glycerol from acrolein, because of the large-scale production of biodiesel from fats, where glycerol is a waste product, the market for glycerol is depressed. Thus, synthetic processes are not economical, owing to oversupply, efforts are being made to convert glycerol to synthetic precursors, such as acrolein and epichlorohydrin. In food and beverages, glycerol serves as a humectant, solvent, and sweetener and it is also used as filler in commercially prepared low-fat foods, and as a thickening agent in liqueurs. Glycerol and water are used to preserve certain types of plant leaves, as a sugar substitute, it has approximately 27 kilocalories per teaspoon and is 60% as sweet as sucrose. It does not feed the bacteria that form plaques and cause dental cavities, as a food additive, glycerol is labeled as E number E422. It is added to icing to prevent it from setting too hard, as used in foods, glycerol is categorized by the Academy of Nutrition and Dietetics as a carbohydrate. The U. S. Food and Drug Administration carbohydrate designation includes all caloric macronutrients excluding protein, glycerol is used in medical, pharmaceutical and personal care preparations, mainly as a means of improving smoothness, providing lubrication, and as a humectant
21.
Methylsulfonylmethane
–
Methylsulfonylmethane is an organosulfur compound with the formula 2SO2. It is also known by other names including DMSO2, methyl sulfone. This colorless solid features the sulfonyl functional group and is considered relatively inert chemically and it occurs naturally in some primitive plants, is present in small amounts in many foods and beverages, and is marketed as a dietary supplement. It is also found in the atmosphere above marine areas, where it is used as a carbon source by the airborne bacteria Afipia. MSM and the corresponding sulfoxide dimethyl sulfoxide have different physical properties, MSM is a white crystalline solid at STP whereas DMSO is a liquid under standard conditions. The sulfoxide is a polar aprotic solvent and is miscible with water. MSM is less reactive than DMSO because the S-atom of the sulfone is already in its highest oxidation state, indeed, oxidation of the sulfoxide produces the sulfone, both under laboratory conditions and metabolically. Because of its polarity and thermal stability, MSM is used industrially as a solvent for both inorganic and organic substances. It is used as a medium in organic synthesis, for example, displacement of aryl chlorides by potassium fluoride can be usefully conducted in molten MSM. With a pKa of 31, it can be deprotonated with sodium amide, the LD50 of MSM is greater than 17.5 grams per kilogram of body weight. In rats, no events were observed after daily doses of 2 g MSM per kg of body weight. In a 90-day follow-up study, rats received daily MSM doses of 1.5 g/kg, nuclear magnetic resonance studies have demonstrated that oral doses of MSM are absorbed into the blood and cross the blood/brain barrier. Published clinical trials of MSM did not report any serious side effects, although no medical uses for MSM have been approved by any government, a variety of health benefits have been claimed and studied. Stanley W. MSM is sold as a supplement and marketed with a variety of claims. According to one review, The benefits claimed far exceed the number of scientific studies and it is hard to build a strong case for its use other than for treating arthritis problems. Moreover, in cases involving topical therapeutics, the role of MSM as an agent, per se. The biochemical effects of supplemental methylsulfonylmethane are poorly understood, some researchers have suggested that MSM has anti-inflammatory effects. The spectrum of effects of dimethyl sulfoxide and MSM differ
22.
Chemical reaction
–
A chemical reaction is a process that leads to the transformation of one set of chemical substances to another. Nuclear chemistry is a sub-discipline of chemistry that involves the reactions of unstable. The substance initially involved in a reaction are called reactants or reagents. Chemical reactions are characterized by a chemical change, and they yield one or more products. Reactions often consist of a sequence of individual sub-steps, the elementary reactions. Chemical reactions are described with chemical equations, which present the starting materials, end products. Chemical reactions happen at a characteristic reaction rate at a given temperature, typically, reaction rates increase with increasing temperature because there is more thermal energy available to reach the activation energy necessary for breaking bonds between atoms. Reactions may proceed in the forward or reverse direction until they go to completion or reach equilibrium, Reactions that proceed in the forward direction to approach equilibrium are often described as spontaneous, requiring no input of free energy to go forward. Non-spontaneous reactions require input of energy to go forward. Different chemical reactions are used in combinations during chemical synthesis in order to obtain a desired product, in biochemistry, a consecutive series of chemical reactions form metabolic pathways. These reactions are catalyzed by protein enzymes. Chemical reactions such as combustion in fire, fermentation and the reduction of ores to metals were known since antiquity, in the Middle Ages, chemical transformations were studied by Alchemists. They attempted, in particular, to lead into gold, for which purpose they used reactions of lead. The process involved heating of sulfate and nitrate minerals such as sulfate, alum. In the 17th century, Johann Rudolph Glauber produced hydrochloric acid and sodium sulfate by reacting sulfuric acid, further optimization of sulfuric acid technology resulted in the contact process in the 1880s, and the Haber process was developed in 1909–1910 for ammonia synthesis. From the 16th century, researchers including Jan Baptist van Helmont, Robert Boyle, the phlogiston theory was proposed in 1667 by Johann Joachim Becher. It postulated the existence of an element called phlogiston, which was contained within combustible bodies. This proved to be false in 1785 by Antoine Lavoisier who found the explanation of the combustion as reaction with oxygen from the air
23.
Concentration
–
In chemistry, concentration is the abundance of a constituent divided by the total volume of a mixture. Several types of mathematical description can be distinguished, mass concentration, molar concentration, number concentration, the term concentration can be applied to any kind of chemical mixture, but most frequently it refers to solutes and solvents in solutions. The molar concentration has variants such as concentration and osmotic concentration. To concentrate a solution, one must add more solute, or reduce the amount of solvent, by contrast, to dilute a solution, one must add more solvent, or reduce the amount of solute. Unless two substances are fully miscible there exists a concentration at which no further solute will dissolve in a solution, at this point, the solution is said to be saturated. If additional solute is added to a solution, it will not dissolve, except in certain circumstances. Instead, phase separation will occur, leading to coexisting phases, the point of saturation depends on many variables such as ambient temperature and the precise chemical nature of the solvent and solute. Concentrations are often called levels, reflecting the mental schema of levels on the axis of a graph. There are four quantities that describe concentration, The mass concentration ρ i is defined as the mass of a constituent m i divided by the volume of the mixture V, ρ i = m i V. The molar concentration c i is defined as the amount of a constituent n i divided by the volume of the mixture V, c i = n i V, however, more commonly the unit mol/L is used. The number concentration C i is defined as the number of entities of a constituent N i in a divided by the volume of the mixture V, C i = N i V. The volume concentration ϕ i is defined as the volume of a constituent V i divided by the volume of the mixture V, ϕ i = V i V. Being dimensionless, it is expressed as a number, e. g.0.18 or 18%, several other quantities can be used to describe the composition of a mixture. Note that these should not be called concentrations, normality is defined as the molar concentration c i divided by an equivalence factor f e q. Since the definition of the equivalence factor depends on context, IUPAC, the SI unit for molality is mol/kg. The mole fraction x i is defined as the amount of a constituent n i divided by the amount of all constituents in a mixture n t o t, x i = n i n t o t. However, the deprecated parts-per notation is used to describe small mole fractions. The mole ratio r i is defined as the amount of a constituent n i divided by the amount of all other constituents in a mixture
24.
Molar concentration
–
A commonly used unit for molar concentration in chemistry is the molar, which is defined as the number of moles per litre. A solution with a concentration of 1 mol/L is equivalent to 1 molar, Molar concentration or molarity is most commonly expressed in units of moles of solute per litre of solution. Or more simply,1 molar =1 M =1 mole/litre, in thermodynamics the use of molar concentration is often not convenient, because the volume of most solutions slightly depends on temperature due to thermal expansion. This problem is resolved by introducing temperature correction factors, or by using a temperature-independent measure of concentration such as molality. The reciprocal quantity represents the dilution which can appear in Ostwalds law of dilution, in the International System of Units the base unit for molar concentration is mol/m3. However, this is impractical for most laboratory purposes and most chemical literature traditionally uses mol/dm3, or mol dm−3, the words millimolar and micromolar refer to mM and μM, respectively. The conversion to number concentration C i is given by, C i = c i ⋅ N A where N A is the Avogadro constant, approximately 6. 022×1023 mol−1. The conversion to mass concentration ρ i is given by, ρ i = c i ⋅ M i where M i is the mass of constituent i. A simpler relation can be obtained by considering the total molar concentration namely the sum of molar concentrations of all the components of the mixture, in an ionic solution, ionic strength is proportional to the sum of molar concentration of salts. The sum of products between these quantities equals one, ∑ i c i ⋅ V i ¯ =1 Molar concentration depends on the variation of the volume of the solution due mainly to thermal expansion. On small intervals of temperature the dependence is, c i = c i, T0 where c i, T0 is the concentration at a reference temperature. Molar and mass concentration have different values in space where diffusion happens, example 1, Consider 11.6 g of NaCl dissolved in 100 g of water. Example 2, Another typical task in chemistry is the preparation of 100 mL of a 2 mol/L solution of NaCl in water, example 3, The density of water is approximately 1000 g/L and its molar mass is 18.02 g/mol. Example 4, A typical protein in bacteria, such as E. coli, may have about 60 copies, and the volume of a bacterium is about 10 −15 L. For example, if a sodium carbonate solution has a concentration of c =1 mol/L. Molar Solution Concentration Calculator Experiment to determine the concentration of vinegar by titration
25.
Metal ions in aqueous solution
–
A metal ion in aqueous solution is a cation, dissolved in water, of chemical formula z+. The solvation number, n, determined by a variety of methods is 4 for Li+. Lanthanide and actinide aqua ions have solvation number of 8 and 9, the strength of the bonds between the metal ion and water molecules in the primary solvation shell increases with the electrical charge, z, on the metal ion and decreases as its radius, r, increases. Aqua ions are subject to hydrolysis, the logarithm of the first hydrolysis constant is proportional to z2/r for most aqua ions. The aqua ion is associated, through hydrogen bonding with water molecules in a secondary solvation shell. Water molecules in the first hydration shell exchange with molecules in the solvation shell. The residence time of a molecule in the first shell varies among the elements from about 100 picoseconds to more than 200 years. Aqua ions are prominent in electrochemistry, most chemical elements are metallic and form simple aqua ions with the formula z+ when the oxidation state is 1,2 or 3. In the highest oxidation state only oxyanions, such as the permanganate ion, in aqueous solution the water molecules directly attached to the metal ion are said to belong to the first coordination sphere, also known as the first, or primary, solvation shell. The bond between a molecule and the metal ion is a dative covalent bond, with the oxygen atom donating both electrons to the bond. Each coordinated water molecule may be attached by hydrogen bonds to water molecules. The latter are said to reside in the coordination sphere. The second coordination sphere is not a well defined entity for ions with charge 1 or 2, in dilute solutions it merges into the water structure in which there is an irregular network of hydrogen bonds between water molecules. The strength of the bond can be estimated in various ways. The hydration enthalpy, though based indirectly on experimental measurements, is the most reliable measure, the scale of values is based on an arbitrarily chosen zero, but this does not affect differences between the values for two metals. Other measures include the M-O vibration frequency and the M-O bond length, the strength of the M-O bond tends to increase with the charge and decrease as the size of the metal ion increases. In fact there is a very good correlation between hydration enthalpy and the ratio of charge squared to ionic radius, z2/r. For ions in solution Shannons effective ionic radius is the measure most often used, water molecules in the first and second solvation shells can exchange places
26.
Solubility
–
Solubility is the property of a solid, liquid, or gaseous chemical substance called solute to dissolve in a solid, liquid, or gaseous solvent. The solubility of a substance depends on the physical and chemical properties of the solute and solvent as well as on temperature, pressure. The solubility of a substance is a different property from the rate of solution. Most often, the solvent is a liquid, which can be a substance or a mixture. One may also speak of solid solution, but rarely of solution in a gas, the extent of solubility ranges widely, from infinitely soluble such as ethanol in water, to poorly soluble, such as silver chloride in water. The term insoluble is often applied to poorly or very poorly soluble compounds, a common threshold to describe something as insoluble is less than 0.1 g per 100 mL of solvent. Under certain conditions, the solubility can be exceeded to give a so-called supersaturated solution. Metastability of crystals can also lead to apparent differences in the amount of a chemical that dissolves depending on its form or particle size. A supersaturated solution generally crystallises when seed crystals are introduced and rapid equilibration occurs, phenylsalicylate is one such simple observable substance when fully melted and then cooled below its fusion point. Solubility is not to be confused with the ability to dissolve a substance, for example, zinc dissolves in hydrochloric acid as a result of a chemical reaction releasing hydrogen gas in a displacement reaction. The zinc ions are soluble in the acid, the smaller a particle is, the faster it dissolves although there are many factors to add to this generalization. Crucially solubility applies to all areas of chemistry, geochemistry, inorganic, physical, organic, in all cases it will depend on the physical conditions and the enthalpy and entropy directly relating to the solvents and solutes concerned. By far the most common solvent in chemistry is water which is a solvent for most ionic compounds as well as a range of organic substances. This is a factor in acidity/alkalinity and much environmental and geochemical work. According to the IUPAC definition, solubility is the composition of a saturated solution expressed as a proportion of a designated solute in a designated solvent. Solubility may be stated in units of concentration such as molarity, molality, mole fraction, mole ratio, mass per volume. Solubility occurs under dynamic equilibrium, which means that solubility results from the simultaneous and opposing processes of dissolution, the solubility equilibrium occurs when the two processes proceed at a constant rate. The term solubility is used in some fields where the solute is altered by solvolysis
27.
Properties of water
–
Water is a polar inorganic compound that is at room temperature a tasteless and odorless liquid, nearly colorless with a hint of blue. This simplest hydrogen chalcogenide is by far the most studied chemical compound and is described as the solvent for its ability to dissolve many substances. This allows it to be the solvent of life and it is the only common substance to exist as a solid, liquid, and gas in nature. Water molecules form hydrogen bonds with other and are strongly polar. This polarity allows it to separate ions in salts and strongly bond to other substances such as alcohols and acids. Water is amphoteric, meaning it is both an acid and a base—it produces H+ and OH− ions by self ionization and this regulates the concentrations of H+ and OH− ions in water. Due to water being a good solvent, it is rarely pure. However, there are many compounds that are essentially, if not completely, insoluble in water, such as fats, oils. The accepted IUPAC name of water is oxidane or simply water, or its equivalent in different languages, oxidane is only intended to be used as the name of the mononuclear parent hydride used for naming derivatives of water by substituent nomenclature. These derivatives commonly have other recommended names, for example, the name hydroxyl is recommended over oxidanyl for the –OH group. The name oxane is explicitly mentioned by the IUPAC as being unsuitable for this purpose, the simplest systematic name of water is hydrogen oxide. This is analogous to related compounds such as hydrogen peroxide, hydrogen sulfide, the polarized form of the water molecule, H+OH−, is also called hydron hydroxide by IUPAC nomenclature. It is a rarely used name of water, and mostly used in various hoaxes or spoofs that call for this chemical to be banned. Other systematic names for water include hydroxic acid, hydroxylic acid, none of these exotic names are used widely. Water is the substance with chemical formula H 2O, one molecule of water has two hydrogen atoms covalently bonded to a single oxygen atom. Water is a tasteless, odorless liquid at ambient temperature and pressure, ice also appears colorless, and water vapor is essentially invisible as a gas. The elements surrounding oxygen in the table, nitrogen, fluorine, phosphorus, sulfur and chlorine. The reason that water forms a liquid is that oxygen is more electronegative than all of elements with the exception of fluorine
28.
Boston
–
Boston is the capital and most populous city of the Commonwealth of Massachusetts in the United States. Boston is also the seat of Suffolk County, although the county government was disbanded on July 1,1999. The city proper covers 48 square miles with a population of 667,137 in 2015, making it the largest city in New England. Alternately, as a Combined Statistical Area, this wider commuting region is home to some 8.1 million people, One of the oldest cities in the United States, Boston was founded on the Shawmut Peninsula in 1630 by Puritan settlers from England. It was the scene of several key events of the American Revolution, such as the Boston Massacre, the Boston Tea Party, the Battle of Bunker Hill, and the Siege of Boston. Upon U. S. independence from Great Britain, it continued to be an important port and manufacturing hub as well as a center for education, through land reclamation and municipal annexation, Boston has expanded beyond the original peninsula. Its rich history attracts many tourists, with Faneuil Hall alone drawing over 20 million visitors per year, Bostons many firsts include the United States first public school, Boston Latin School, first subway system, the Tremont Street Subway, and first public park, Boston Common. Bostons economic base also includes finance, professional and business services, biotechnology, information technology, the city has one of the highest costs of living in the United States as it has undergone gentrification, though it remains high on world livability rankings. Bostons early European settlers had first called the area Trimountaine but later renamed it Boston after Boston, Lincolnshire, England, the renaming on September 7,1630 was by Puritan colonists from England who had moved over from Charlestown earlier that year in quest of fresh water. Their settlement was limited to the Shawmut Peninsula, at that time surrounded by the Massachusetts Bay and Charles River. The peninsula is thought to have been inhabited as early as 5000 BC, in 1629, the Massachusetts Bay Colonys first governor John Winthrop led the signing of the Cambridge Agreement, a key founding document of the city. Puritan ethics and their focus on education influenced its early history, over the next 130 years, the city participated in four French and Indian Wars, until the British defeated the French and their Indian allies in North America. Boston was the largest town in British America until Philadelphia grew larger in the mid-18th century, Bostons harbor activity was significantly curtailed by the Embargo Act of 1807 and the War of 1812. Foreign trade returned after these hostilities, but Bostons merchants had found alternatives for their investments in the interim. Manufacturing became an important component of the economy, and the citys industrial manufacturing overtook international trade in economic importance by the mid-19th century. Boston remained one of the nations largest manufacturing centers until the early 20th century, a network of small rivers bordering the city and connecting it to the surrounding region facilitated shipment of goods and led to a proliferation of mills and factories. Later, a network of railroads furthered the regions industry. Boston was a port of the Atlantic triangular slave trade in the New England colonies
29.
Houghton Mifflin Harcourt
–
Houghton Mifflin Harcourt is an educational and trade publisher in the United States. Headquartered in Bostons Back Bay, it publishes textbooks, instructional materials, assessments, reference works. The company was known as Houghton Mifflin Company but changed its name following the 2007 acquisition of Harcourt Publishing. Prior to March 2010, it was a subsidiary of Education Media and Publishing Group Limited, in 1832, William Ticknor and James Thomas Fields had gathered an impressive list of writers, including Ralph Waldo Emerson, Nathaniel Hawthorne, and Henry David Thoreau. The duo formed a relationship with Riverside Press, a Boston printing company owned by Henry Oscar Houghton. Shortly after, Houghton also founded a company with partner George Mifflin. The company still had debt from when it merged from Houghton, Osgood and Company, in 1884, James D. Hurd, the son of Melancthon Hurd became a partner. Three people in 1888 became partners as well, James Murray Kay, Thurlow Weed Barnes, shortly thereafter the company established an Educational Department, and from 1891 to 1908 sales of educational materials increased by 500 percent. Soon after 1916, Houghton Mifflin became involved in publishing standardized tests and testing materials, the company was the fourth-largest educational publisher in the United States in 1921. In 1961, Houghton Mifflin famously passed on Julia Childs Mastering the Art of French Cooking, giving it up to Alfred A. Knopf who later published it in 1962. It went on to become a success and is considered by many to be the bible of French cooking. Houghton Mifflins strategic error was depicted in the 2009 film Julie & Julia, in 1967, Houghton Mifflin became a publicly traded company on the New York Stock Exchange under the stock symbol HTN. Under president Nader F. Darehshori Houghton Mifflin acquired in 1994 for $138 million McDougal Littell, a publisher of secondary school materials. Heath and Company, a publisher of educational resources. In 1996, the company created their Great Source Education Group to combine the supplemental material product lines of their School Division and these two companies. In 1998, HMH announced a sub-brand called LOGAL Software, which was to release a new line of interactive science software called Science Gateways, as of 2017, Houghton Mifflin Harcourt is offering the Logal Science brand as a licensing opportunity on its website. Mergers and acquisitions activities have had effects on this company. In 2001, Houghton Mifflin was acquired by French media giant Vivendi Universal for $2.2 billion including assumed debt, on December 22,2006, it was announced that Riverdeep PLC had completed its acquisition of Houghton Mifflin
30.
Solid solution
–
A solid solution is a solid-state solution of one or more solutes in a solvent. The solid solution needs to be distinguished from a mechanical mixtures of powdered solids like two salts, sugar and salt, etc, the mechanical mixtures have total or partial miscibility gap in solid state. Examples of solid solutions include crystallized salts from their liquid mixture, metal alloys, in the case of metal alloys intermetallic compounds occur frequently. The solute may incorporate into the solvent crystal lattice substitutionally, by replacing a solvent particle in the lattice, or interstitially, by fitting into the space between solvent particles. Both of these types of solid solution affect the properties of the material by distorting the crystal lattice, some mixtures will readily form solid solutions over a range of concentrations, while other mixtures will not form solid solutions at all. The propensity for any two substances to form a solution is a complicated matter involving the chemical, crystallographic. 1 displays an alloy of two metals which forms a solution at all relative concentrations of the two species. Solid solutions have important commercial and industrial applications, as such mixtures often have superior properties to pure materials, many metal alloys are solid solutions. Even small amounts of solute can affect the electrical and physical properties of the solvent, the binary phase diagram in Fig.2 shows the phases of a mixture of two substances in varying concentrations, A and B. The region labeled α is a solution, with B acting as the solute in a matrix of A. On the other end of the scale, the region labeled β is also a solid solution. The large solid region in between the α and β solid solutions, labeled α + β, is not a solid solution, at other proportions, the material will enter a mushy or pasty phase until it warms up to being completely melted. The mixture at the dip point of the diagram is called a eutectic alloy, lead-tin mixtures formulated at that point are useful when soldering electronic components, particularly if done manually, since the solid phase is quickly entered as the solder cools. In contrast, when lead-tin mixtures were used to solder seams in automobile bodies a pasty state enabled a shape to be formed with a paddle or tool. When a solid solution becomes unstable — due to a temperature, for example — exsolution occurs. This is mainly caused by difference in cation size, cations which have a large difference in radii are not likely to readily substitute. Take the alkali feldspar minerals for example, whose end members are albite, NaAlSi3O8 and microcline and this leads to exsolution where they will separate into two separate phases. In the case of the feldspar minerals, thin white albite layers will alternate between typically pink microcline
31.
Buffer solution
–
For an individual weak acid or weak base component, see Buffering agent. For uses not related to chemistry, see Buffer. A buffer solution is an aqueous solution consisting of a mixture of an acid and its conjugate base. Its pH changes very little when a small amount of acid or base is added to it. Buffer solutions are used as a means of keeping pH at a constant value in a wide variety of chemical applications. In nature, there are systems that use buffering for pH regulation. For example, the buffering system is used to regulate the pH of blood. Buffer solutions achieve their resistance to pH change because of the presence of an equilibrium between the acid HA and its conjugate base A−. HA ⇌ H+ + A− When some strong acid is added to a mixture of the weak acid and its conjugate base. Because of this, the ion concentration increases by less than the amount expected for the quantity of strong acid added. Similarly, if strong alkali is added to the mixture the hydrogen ion concentration decreases by less than the amount expected for the quantity of alkali added, the effect is illustrated by the simulated titration of a weak acid with pKa =4.7. The relative concentration of undissociated acid is shown in blue and of its base in red. The pH changes relatively slowly in the region, pH = pKa ±1. OH− + H+ → H2O Once the acid is more than 95% deprotonated the pH rises rapidly because most of the alkali is consumed in the neutralization reaction. Buffer capacity, β, is a measure of the resistance of a buffer solution to pH change on addition of hydroxide ions. It can be defined as follows, β = d n d where dn is an infinitesimal amount of added base and d is the resulting infinitesimal change in the cologarithm of the hydrogen ion concentration. With this definition the buffer capacity of an acid, with a dissociation constant Ka. This equation shows that there are three regions of raised buffer capacity, at very low p the term in the denominator predominates and buffer capacity rises exponentially with decreasing pH
32.
Colloid
–
A colloid, in chemistry, is a mixture in which one substance of microscopically dispersed insoluble particles is suspended throughout another substance. Sometimes the dispersed substance alone is called the colloid, the colloidal suspension refers unambiguously to the overall mixture. Unlike a solution, whose solute and solvent constitute only one phase, a colloid has a dispersed phase, to qualify as a colloid, the mixture must be one that does not settle or would take a very long time to settle appreciably. The dispersed-phase particles have a diameter between approximately 1 and 1000 nanometers, such particles are normally easily visible in an optical microscope, although at the smaller size range, an ultramicroscope or an electron microscope may be required. Homogeneous mixtures with a phase in this size range may be called colloidal aerosols, colloidal emulsions, colloidal foams, colloidal dispersions. The dispersed-phase particles or droplets are affected largely by the surface chemistry present in the colloid, some colloids are translucent because of the Tyndall effect, which is the scattering of light by particles in the colloid. Other colloids may be opaque or have a slight color, Colloidal suspensions are the subject of interface and colloid science. This field of study was introduced in 1861 by Scottish scientist Thomas Graham, because of the size exclusion, the colloidal particles are unable to pass through the pores of an ultrafiltration membrane with a size smaller than their own dimension. The smaller the size of the pore of the ultrafiltration membrane, the measured value of the concentration of a truly dissolved species will thus depend on the experimental conditions applied to separate it from the colloidal particles also dispersed in the liquid. This is particularly important for solubility studies of readily hydrolyzed species such as Al, Eu, Am, Cm, the colloid particles are attracted toward water. They are also called reversible sols, hydrophobic colloids, These are opposite in nature to hydrophilic colloids. The colloid particles are repelled by water and they are also called irreversible sols. In some cases, a colloid suspension can be considered a homogeneous mixture and this is because the distinction between dissolved and particulate matter can be sometimes a matter of approach, which affects whether or not it is homogeneous or heterogeneous. The following forces play an important role in the interaction of particles, Excluded volume repulsion. Electrostatic interaction, Colloidal particles often carry a charge and therefore attract or repel each other. The charge of both the continuous and the phase, as well as the mobility of the phases are factors affecting this interaction. Van der Waals forces, This is due to interaction between two dipoles that are permanent or induced. Even if the particles do not have a permanent dipole, fluctuations of the electron density gives rise to a dipole in a particle
33.
Phase diagram
–
For the use of this term in mathematics and physics, see phase space. Common components of a phase diagram are lines of equilibrium or phase boundaries, phase transitions occur along lines of equilibrium. Triple points are points on phase diagrams where lines of equilibrium intersect, triple points mark conditions at which three different phases can coexist. For example, the phase diagram has a triple point corresponding to the single temperature and pressure at which solid, liquid. The solidus is the temperature below which the substance is stable in the solid state, the liquidus is the temperature above which the substance is stable in a liquid state. There may be a gap between the solidus and liquidus, within the gap, the substance consists of a mixture of crystals, the simplest phase diagrams are pressure–temperature diagrams of a single simple substance, such as water. The axes correspond to the pressure and temperature, the phase diagram shows, in pressure–temperature space, the lines of equilibrium or phase boundaries between the three phases of solid, liquid, and gas. The fusion curves for water and Antimony are with negative slopes, the curves on the phase diagram show the points where the free energy becomes non-analytic, their derivatives with respect to the coordinates change discontinuously. For example, the capacity of a container filled with ice will change abruptly as the container is heated past the melting point. The open spaces, where the energy is analytic, correspond to single phase regions. Single phase regions are separated by lines of non-analytical behavior, where phase transitions occur, in the diagram on the left, the phase boundary between liquid and gas does not continue indefinitely. Instead, it terminates at a point on the diagram called the critical point. This reflects the fact that, at high temperatures and pressures. In water, the critical point occurs at around Tc =647.096 K, pc =22.064 MPa, the existence of the liquid–gas critical point reveals a slight ambiguity in labelling the single phase regions. Thus, the liquid and gaseous phases can blend continuously into each other, the solid–liquid phase boundary can only end in a critical point if the solid and liquid phases have the same symmetry group. Thus, the substance requires a temperature for its molecules to have enough energy to break out of the fixed pattern of the solid phase. A similar concept applies to liquid–gas phase changes, water, because of its particular properties, is one of the several exceptions to the rule. In addition to temperature and pressure, other properties may be graphed in phase diagrams
34.
Eutectic system
–
It is only in this atomic/molecular ratio that the eutectic system melts as a whole, at a specific temperature the super-lattice releasing at once all its components into a liquid mixture. The eutectic temperature is the lowest possible melting temperature over all of the ratios for the involved component species. Conversely, as a non-eutectic mixture cools down, each component will solidify at a distinct temperature. The coordinates defining a eutectic point on a phase diagram are the percentage ratio. Not all binary alloys have eutectic points because the electrons of the component species are not always compatible, in any mixing ratio. The term eutectic was coined in 1884 by British physicist and chemist Frederick Guthrie, tangibly, this means the liquid and two solid solutions all coexist at the same time and are in chemical equilibrium. There is also a thermal arrest for the duration of the change of phase during which the temperature of the system does not change, the resulting solid macrostructure from a eutectic reaction depends on a few factors. The most important factor is how the two solid solutions nucleate and grow, the most common structure is a lamellar structure, but other possible structures include rodlike, globular, and acicular. Compositions of eutectic systems that are not at the composition can be classified as hypoeutectic or hypereutectic. As the temperature of a composition is lowered the liquid mixture will precipitate one component of the mixture before the other. In a hypereutectic solution, there will be a phase of species β whereas a hypoeutectic solution will have a proeutectic α phase. Eutectic alloys have two or more materials and have a eutectic composition, when a non-eutectic alloy solidifies, its components solidify at different temperatures, exhibiting a plastic melting range. Conversely, when a well-mixed, eutectic alloy melts, it does so at a single, some uses include, NEMA Eutectic Alloy Overload Relays for electrical protection of 3-phase motors for pumps, fans, conveyors, and other factory process equipment. The eutectic nature of salt and water is exploited when salt is spread on roads to aid snow removal, ethanol–water has an unusually biased eutectic point, i. e. it is close to pure ethanol, which sets the maximum proof obtainable by fractional freezing. Solar salt, 60% NaNO3 and 40% KNO3, forms a eutectic molten salt mixture which is used for energy storage in concentrated solar power plants. To reduce the melting point in the solar molten salts calcium nitrate is used in the following proportion, 42% Ca2, 43% KNO3. Lidocaine and prilocaine—both are solids at room temperature—form a eutectic that is an oil with a 16 °C melting point that is used in mixture of local anesthetic preparations. Menthol and camphor, both solids at room temperature, form a eutectic that is a liquid at room temperature in the proportions,8,2,7,3,6,4
35.
Alloy
–
An alloy is a mixture of metals or a mixture of a metal and another element. Alloys are defined by a metallic bonding character, an alloy may be a solid solution of metal elements or a mixture of metallic phases. Intermetallic compounds are alloys with a stoichiometry and crystal structure. Zintl phases are sometimes considered alloys depending on bond types. Alloys are used in a variety of applications. In some cases, a combination of metals may reduce the overall cost of the material while preserving important properties, in other cases, the combination of metals imparts synergistic properties to the constituent metal elements such as corrosion resistance or mechanical strength. Examples of alloys are steel, solder, brass, pewter, duralumin, bronze, the alloy constituents are usually measured by mass. Alloys are usually classified as substitutional or interstitial alloys, depending on the arrangement that forms the alloy. They can be classified as homogeneous, or heterogeneous or intermetallic. An alloy is a mixture of elements, which forms an impure substance that retains the characteristics of a metal. Alloys are made by mixing two or more elements, at least one of which is a metal and this is usually called the primary metal or the base metal, and the name of this metal may also be the name of the alloy. The other constituents may or may not be metals but, when mixed with the base, they will be soluble. The mechanical properties of alloys will often be different from those of its individual constituents. A metal that is very soft, such as aluminium, can be altered by alloying it with another soft metal. Although both metals are soft and ductile, the resulting aluminium alloy will have much greater strength. Adding a small amount of carbon to iron trades its great ductility for the greater strength of an alloy called steel. Due to its strength, but still substantial toughness, and its ability to be greatly altered by heat treatment, steel is one of the most useful. By adding chromium to steel, its resistance to corrosion can be enhanced, creating stainless steel, while adding silicon will alter its electrical characteristics, producing silicon steel
36.
Saturation (chemistry)
–
In chemistry, saturation has diverse meanings, all based on the idea of reaching a maximum capacity. In organic chemistry, a compound is a hydrocarbon which has no double or triple bonds. For example, consider three similar organic compounds that are less saturated, ethane, ethylene, and ethyne. Ethane, a saturated compound, has only single bonds between its hydrogen and carbon atoms. Ethylene, a compound of ethane, has a carbon double bond. Finally ethyne, the completely unsaturated compound of ethane, has a triple bond. The concept of saturation can be described using various naming systems, formulas, for instance, IUPAC nomenclature is a system of naming conventions used to describe the type and location of unsaturation within organic compounds. The degree of unsaturation is a used to summarize and diagram the amount of hydrogen that a compound can bind. Unsaturation can be determined by NMR, mass spectrometry and IR spectroscopy, tallow consists mainly of triglycerides, whose major constituents are derived from the saturated stearic and monounsaturated oleic acids. Many vegetable oils contain fatty acids with one or more double bonds in them, in organometallic chemistry, an unsaturated complex has fewer than 18 valence electrons and thus is susceptible to oxidative addition or coordination of an additional ligand. Unsaturation is characteristic of many catalysts because it is usually a requirement for substrate activation, in contrast, a coordinatively saturated complex resists undergoing substitution and oxidative addition reactions. In physical chemistry, saturation is the point at which the solute of a substance can dissolve no more of that substance and additional amounts of it will appear as a separate phase. This point of concentration, the saturation point, depends on the temperature and pressure of the solution as well as the chemical nature of the substances involved. Impurities, being present in lower concentration, do not saturate the solvent. If a change in conditions means that the concentration is higher than the saturation point. In physical chemistry, when referring to processes, saturation denotes the degree at which a binding site is fully occupied. For example, base refers to the fraction of exchangeable cations that are base cations. In biochemistry, the saturation refers to the fraction of total protein binding sites that are occupied at any given time
37.
Supersaturation
–
Supersaturation is a state of a solution that contains more of the dissolved material than could be dissolved by the solvent under normal circumstances. It can also refer to a vapor of a compound that has a higher pressure than the pressure of that compound. Special conditions need to be met in order to generate a supersaturated solution, one of the easiest ways to do this relies on the temperature dependence of solubility. As a general rule, the heat is added to a system. Therefore, at high temperatures, more solute can be dissolved than at room temperature, the precipitation or crystallization of the solute takes longer than the actual cooling time because the molecules need to meet up and form the precipitate without being knocked apart by water. Thus, the larger the molecule, the longer it will take to crystallize due to the principles of Brownian motion, the condition of supersaturation does not necessarily have to be reached through the manipulation of heat. The ideal gas law suggests that pressure and volume can also be changed to force a system into a supersaturated state, if the volume of solvent is decreased, the concentration of the solute can be above the saturation point and thus create a supersaturated solution. The decrease in volume is most commonly generated through evaporation, similarly, an increase in pressure can drive a solution to a supersaturated state. All three of these rely on the fact that the conditions of the solution can be changed quicker than the solute can precipitate or crystallize out. Supersaturated solutions will also undergo crystallization under specific conditions, in a normal solution, once the maximum amount of solute is dissolved, adding more solute would either cause the dissolved solute to precipitate out and/or for the solute to not dissolve at all. Similarly, there are cases wherein solubility of a solution is decreased by manipulating temperature, pressure, or volume. In these cases, the solute will simply precipitate out and this is due to the fact that a supersaturated solution is in a higher energy state than a saturated solution. Crystallization will occur to allow the solution to reach an energy state. The activation energy comes in the form of a crystal being added to the liquid solution. This nuclei can be added from another source, which is known as seeding, or can spontaneously form within the solution due partly to ion. This process is known as primary nucleation and it is necessary for the nuclei to be identical to the solute that is crystallizing. This will allow for the ions to build up on the nuclei. There are a multitude of factors that affect the rate and order of magnitude with which crystallization proceeds as well as the difference in formation of crystallites
38.
Apparent molar property
–
An apparent molar property of a solution component in a mixture or solution is a quantity defined with the purpose of isolating the contribution of each component to the non-ideality of the mixture. It shows the change in the corresponding solution property when all of that component is added to the solution, however this assumption is often not justified, since the values of apparent molar properties of a component may be quite different from its molar properties in the pure state. This equation serves as the definition of ϕ V ~1, the first term is equal to the volume of the same quantity of solvent with no solute, and the second term is the change of volume on addition of the solute. ϕ V ~1 may then be considered as the volume of the solute if it is assumed that the molar volume of the solvent is unchanged by the addition of solute. However this assumption must often be considered unrealistic as shown in the Examples below, an apparent molar quantity can be similarly defined for the component identified as solvent ϕ V ~0. Some authors have reported apparent molar volumes of both components of the same solution, apparent quantities can also be expressed using mass instead of number of moles. This expression produces apparent specific quantities, like the apparent specific volume, V = V0 + ϕ V1 = v 0 m 0 + ϕ v 1 m 1 where the specific quantities are denoted with small letters. Apparent properties are not constants, but are functions of the composition, at infinite dilution, an apparent molar property and the corresponding partial molar property become equal. Some apparent molar properties that are used are apparent molar enthalpy, apparent molar heat capacity. The apparent volume of a solute can be expressed as a function of the molality b of that solute, the volume of solution per mole of solute is 1 ρ. V1 ¯ = ϕ V ~1 + b ∂ ϕ V ~1 ∂ b, for instance, solid NaCl has a volume of 27 cm3 per mole, but the apparent molar volume at low concentrations is only 16.6 cc/mole. In fact, some aqueous electrolytes have negative apparent molar volumes, NaOH -6.7, LiOH -6.0 and this means that their solutions in a given amount of water have a smaller volume than the same amount of pure water. The physical reason is that water molecules are strongly attracted to the ions so that they occupy less space. Another example of the apparent molar volume of the component being less than its molar volume as a pure substance is the case of ethanol in water. For example, at 20 mass-percent ethanol, the solution has a volume of 1.0326 litres per kg at 20 °C, the apparent volume of the added ethanol is 1.0326 L -0.8 kg x 1.0018 L/kg =0.2317 L. The number of moles of ethanol is 0.2 kg / =4.341 mol, however pure ethanol has a molar volume at this temperature of 58.4 cc/mole. The nonideality of the solution is reflected by a decrease in the volume of the combined system upon mixing. As the percent ethanol goes up toward 100%, the apparent molar volume rises to the volume of pure ethanol
