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 fundamentally depends on the physical and chemical properties of the solute and solvent as well as on temperature and presence of other chemicals of the solution; the extent of the solubility of a substance in a specific solvent is measured as the saturation concentration, where adding more solute does not increase the concentration of the solution and begins to precipitate the excess amount of solute. Insolubility is the inability to dissolve in a liquid or gaseous solvent. Most the solvent is a liquid, which can be a pure substance or a mixture. One may speak of solid solution, but of solution in a gas. Under certain conditions, the equilibrium solubility can be exceeded to give a so-called supersaturated solution, metastable. Metastability of crystals can lead to apparent differences in the amount of a chemical that dissolves depending on its crystalline form or particle size.
A supersaturated solution crystallises when'seed' crystals are introduced and rapid equilibration occurs. Phenylsalicylate is one such simple observable substance when melted and cooled below its fusion point. Solubility is not to be confused with the ability to'dissolve' a substance, because the solution might occur because of a chemical reaction. 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 solubility of a substance is an different property from the rate of solution, how fast it dissolves; 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, inorganic, physical and biochemistry. 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, a solvent for most ionic compounds as well as a wide range of organic substances.
This is a crucial factor in much environmental and geochemical work. According to the IUPAC definition, solubility is the analytical composition of a saturated solution expressed as a proportion of a designated solute in a designated solvent. Solubility may be stated in various units of concentration such as molarity, mole fraction, mole ratio, mass per volume and other units; the extent of solubility ranges from infinitely soluble such as ethanol in water, to poorly soluble, such as silver chloride in water. The term insoluble is applied to poorly or poorly soluble compounds. A number of other descriptive terms are used to qualify the extent of solubility for a given application. For example, U. S. Pharmacopoeia gives the following terms: The thresholds to describe something as insoluble, or similar terms, may depend on the application. For example, one source states that substances are described as "insoluble" when their solubility is less than 0.1 g per 100 mL of solvent. Solubility occurs under dynamic equilibrium, which means that solubility results from the simultaneous and opposing processes of dissolution and phase joining.
The solubility equilibrium occurs. The term solubility is used in some fields where the solute is altered by solvolysis. For example, many metals and their oxides are said to be "soluble in hydrochloric acid", although in fact the aqueous acid irreversibly degrades the solid to give soluble products, it is true that most ionic solids are dissolved by polar solvents, but such processes are reversible. In those cases where the solute is not recovered upon evaporation of the solvent, the process is referred to as solvolysis; the thermodynamic concept of solubility does not apply straightforwardly to solvolysis. When a solute dissolves, it may form several species in the solution. For example, an aqueous suspension of ferrous hydroxide, Fe2, will contain the series + as well as other species. Furthermore, the solubility of ferrous hydroxide and the composition of its soluble components depend on pH. In general, solubility in the solvent phase can be given only for a specific solute, thermodynamically stable, the value of the solubility will include all the species in the solution.
Solubility is defined for specific phases. For example, the solubility of aragonite and calcite in water are expected to differ though they are both polymorphs of calcium carbonate and have the same chemical formula; the solubility of one substance in another is determined by the balance of intermolecular forces between the solvent and solute, the entropy change that accompanies the solvation. Factors such as temperature and pressure will alter this balance. Solubility may strongly depend on the presence of other species dissolved in the solvent, for example, complex-forming anions in liquids. Solubility will depend on the excess or deficiency of a common ion in the solution, a phenomenon known as the common-ion effect. To a lesser extent, solubility will depend on the ionic strength of solutions; the last two effects can be quantified using the equation for solubility equilibrium. For a solid that dissolves in a redox reaction, solubility is expe
The Jmol applet, among other abilities, offers an alternative to the Chime plug-in, no longer under active development. While Jmol has many features that Chime lacks, it does not claim to reproduce all Chime functions, most notably, the Sculpt mode. Chime requires plug-in installation and Internet Explorer 6.0 or Firefox 2.0 on Microsoft Windows, or Netscape Communicator 4.8 on Mac OS 9. Jmol operates on a wide variety of platforms. For example, Jmol is functional in Mozilla Firefox, Internet Explorer, Google Chrome, Safari. Chemistry Development Kit Comparison of software for molecular mechanics modeling Jmol extension for MediaWiki List of molecular graphics systems Molecular graphics Molecule editor Proteopedia PyMOL SAMSON Official website Wiki with listings of websites and moodles Willighagen, Egon. "Fast and Scriptable Molecular Graphics in Web Browsers without Java3D". Doi:10.1038/npre.2007.50.1
Salt is a mineral composed of sodium chloride, a chemical compound belonging to the larger class of salts. Salt is present in vast quantities in seawater; the open ocean has about 35 grams of solids per liter of sea water, a salinity of 3.5%. Salt is essential for life in general, saltiness is one of the basic human tastes. Salt is one of the oldest and most ubiquitous food seasonings, salting is an important method of food preservation; some of the earliest evidence of salt processing dates to around 6,000 BC, when people living in the area of present-day Romania boiled spring water to extract salts. Salt was prized by the ancient Hebrews, the Greeks, the Romans, the Byzantines, the Hittites and the Indians. Salt became an important article of trade and was transported by boat across the Mediterranean Sea, along specially built salt roads, across the Sahara on camel caravans; the scarcity and universal need for salt have led nations to go to war over it and use it to raise tax revenues. Salt has other cultural and traditional significance.
Salt is processed from salt mines, by the evaporation of seawater and mineral-rich spring water in shallow pools. Its major industrial products are caustic chlorine. Of the annual global production of around two hundred million tonnes of salt, about 6% is used for human consumption. Other uses include water conditioning processes, de-icing highways, agricultural use. Edible salt is sold in forms such as sea salt and table salt which contains an anti-caking agent and may be iodised to prevent iodine deficiency; as well as its use in cooking and at the table, salt is present in many processed foods. Sodium is an essential nutrient for human health via its role as an osmotic solute. Excessive salt consumption may increase the risk of cardiovascular diseases, such as hypertension, in children and adults; 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, equivalent to 5 grams of salt per day.
All through history, the availability of salt has been pivotal to civilization. What is now thought to have been the first city in Europe is Solnitsata, in Bulgaria, a salt mine, providing the area now known as the Balkans with salt since 5400 BC; the name Solnitsata means "salt works". While people have used canning and artificial refrigeration to preserve food for the last hundred years or so, salt has been the best-known food preservative for meat, for many thousands of years. A ancient salt-works operation has been discovered at the Poiana Slatinei archaeological site next to a salt spring in Lunca, Neamț County, Romania. Evidence indicates that Neolithic people of the Precucuteni Culture were boiling the salt-laden spring water through the process of briquetage to extract the salt as far back as 6050 BC; the salt extracted from this operation may have had a direct correlation to the rapid growth of this society's population soon after its initial production began. The harvest of salt from the surface of Xiechi Lake near Yuncheng in Shanxi, dates back to at least 6000 BC, making it one of the oldest verifiable saltworks.
There is more salt in animal tissues, such as meat and milk, than in plant tissues. Nomads who subsist on their flocks and herds do not eat salt with their food, but agriculturalists, feeding on cereals and vegetable matter, need to supplement their diet with salt. With the spread of civilization, salt became one of the world's main trading commodities, it was of high value to the ancient Hebrews, the Greeks, the Romans, the Byzantines, the Hittites and other peoples of antiquity. In the Middle East, salt was used to ceremonially seal an agreement, the ancient Hebrews made a "covenant of salt" with God and sprinkled salt on their offerings to show their trust in him. An ancient practice in time of war was salting the earth: scattering salt around in a defeated city to prevent plant growth; the Bible tells the story of King Abimelech, ordered by God to do this at Shechem, various texts claim that the Roman general Scipio Aemilianus Africanus ploughed over and sowed the city of Carthage with salt after it was defeated in the Third Punic War.
Salt may have been used for barter in connection with the obsidian trade in Anatolia in the Neolithic Era. Salt was included among funeral offerings found in ancient Egyptian tombs from the third millennium BC, as were salted birds, salt fish. From about 2800 BC, the Egyptians began exporting salt fish to the Phoenicians in return for Lebanon cedar and the dye Tyrian purple. Herodotus described salt trading routes across Libya back in the 5th century BC. In the early years of the Roman Empire, roads were built for the transportation of salt from the salt imported at Ostia to the capital. In Africa, salt was used as currency south of the Sahara, slabs of rock salt were used as coins in Abyssinia. Moorish merchants in the 6th century traded salt for weight for weight; the Tuareg have traditionally maintained routes across the Sahara for the transportation of salt by Azalai. The caravans
An odor, or odour, is caused by one or more volatilized chemical compounds that are found in low concentrations that humans and animals can perceive by their sense of smell. An odor is called a "smell" or a "scent", which can refer to either a pleasant or an unpleasant odor. While "scent" can refer to pleasant and unpleasant odors, the terms "scent", "aroma", "fragrance" are reserved for pleasant-smelling odors and are used in the food and cosmetic industry to describe floral scents or to refer to perfumes. In the United Kingdom, "odour" refers to scents in general. An unpleasant odor can be described as "reeking" or called a "malodor", "stench", "pong", or "stink"; the perception of odors, or sense of smell, is mediated by the olfactory nerve. The olfactory receptor cells are neurons present in the olfactory epithelium, a small patch of tissue at the back of the nasal cavity. There are millions of olfactory receptor neurons; each neuron has cilia in direct contact with the air. Odorous molecules bind to receptor proteins extending from cilia and act as a chemical stimulus, initiating electric signals that travel along the olfactory nerve's axons to the brain.
When an electrical signal reaches a threshold, the neuron fires, which sends a signal traveling along the axon to the olfactory bulb, a part of the limbic system of the brain. Interpretation of the smell begins there, relating the smell to past experiences and in relation to the substance inhaled; the olfactory bulb acts as a relay station connecting the nose to the olfactory cortex in the brain. Olfactory information is further processed and forwarded to the central nervous system, which controls emotions and behavior as well as basic thought processes. Odor sensation depends on the concentration available to the olfactory receptors. A single odorant is recognized by many receptors. Different odorants are recognized by combinations of receptors; the patterns of neuron signals help to identify the smell. The olfactory system does not interpret a single compound, but instead the whole odorous mix; this does not correspond to the intensity of any single constituent. Most odors consists of organic compounds, although some simple compounds not containing carbon, such as hydrogen sulfide and ammonia, are odorants.
The perception of an odor effect is a two-step process. First, there is the physiological part; this is the detection of stimuli by receptors in the nose. The stimuli are recognized by the region of the human brain; because of this, an objective and analytical measure of odor is impossible. While odor feelings are personal perceptions, individual reactions are related, they relate to things such as gender, state of health, personal history. The ability to identify odor varies among decreases with age. Studies show there are sex differences in odor discrimination, women outperform men. Pregnant women have increased smell sensitivity, sometimes resulting in abnormal taste and smell perceptions, leading to food cravings or aversions; the ability to taste decreases with age as the sense of smell tends to dominate the sense of taste. Chronic smell problems are reported in small numbers for those in their mid-twenties, with numbers increasing with overall sensitivity beginning to decline in the second decade of life, deteriorating appreciably as age increases once over 70 years of age.
For most untrained people, the process of smelling gives little information concerning the specific ingredients of an odor. Their smell perception offers information related to the emotional impact. Experienced people, such as flavorists and perfumers, can pick out individual chemicals in complex mixtures through smell alone. Odor perception is a primal sense; the sense of smell enables pleasure, can subconsciously warn of danger, help locate mates, find food, or detect predators. Humans have a good sense of smell, correlated to an evolutionary decline in sense of smell. A human's sense of smell is just as good as many animals and can distinguish a diversity of odors—approximately 10,000 scents. Studies reported. Odors that a person is used to, such as their own body odor, are less noticeable than uncommon odors; this is due to habituation. After continuous odor exposure, the sense of smell is fatigued, but recovers if the stimulus is removed for a time. Odors can change due to environmental conditions: for example, odors tend to be more distinguishable in cool dry air.
Habituation affects the ability to distinguish odors after continuous exposure. The sensitivity and ability to discriminate odors diminishes with exposure, the brain tends to ignore continuous stimulus and focus on differences and changes in a particular sensation; when odorants are mixed, a habitual odorant is blocked. This depends on the strength of the odorants in the mixture, which can change the perception and processing of an odor; this process helps classify similar odors as well as adjust sensitivity to differences in complex stimuli. The primary gene sequences for thousands of olfactory receptors are known for the genomes of more than a dozen organisms, they are seven-helix-turn transmembrane proteins. But there are no known structures for any olfactory receptor. There is a conserved sequence in three quarters of all ORs; this is a tripodal metal-ion binding site, and
Sodium metabisulfite or sodium pyrosulfite is an inorganic compound of chemical formula Na2S2O5. The substance is sometimes referred to as disodium metabisulfite, it is used as a disinfectant and preservative agent. Sodium metabisulfite can be prepared by evaporating a solution of sodium bisulfite saturated with sulfur dioxide: 2 HSO3− ⇌ H2O + S2O52−which yields a residue of colorless solid Na2S2O5; the anion metabisulfite is a hybrid of dithionate. The anion consists of an SO2 group linked to an SO3 group, with the negative charge more localized on the SO3 end; the S–S bond length is 2.22 Å, the "thionate" and "thionite" S–O distances are 1.46 and 1.50 Å respectively. It is used as a preservative and antioxidant in food and is known as E223, it may cause allergic reactions in those who are sensitive to sulfites, including respiratory reactions in asthmatics and other allergic reactions in sensitive individuals. Sodium metabisulfite and potassium metabisulfite are the primary ingredients in Campden tablets, used for wine and beer making.
The acceptable daily intake is up to 0.7 milligrams per kilogram of body weight. Sodium metabisulfite oxidizes in the liver to sulfate, excreted in the urine, it is used in homebrewing and winemaking to sanitize equipment. It is used as a cleaning agent for potable water reverse osmosis membranes in desalination systems, it is used to remove chloramine from drinking water after treatment. Added to local anaesthetic solutions to prevent oxidation of vasoconstrictor adrenaline and thus improve the shelf life of the solution It is used in photography. Concentrated sodium metabisulfite can be used to remove tree stumps; some brands contain 98% sodium metabisulfite, cause degradation of lignin in the stumps, facilitating removal. It is used as an excipient in some tablets, such as paracetamol. 0.5 mg is used in epinephrine autoinjectors such as the EpiPen. A important health related aspect of this substance is that it can be added to a blood smear in a test for sickle cell anaemia; the substances causes defunct cells to sickle hence confirming disease.
It is used as the source of SO2 in wine, an important anti-oxidant and bactericide It is used to precipitate gold from auric acid. It is used in waste treatment to chemically reduce hexavalent chromium to trivalent chromium which can be precipitated and removed from an aqueous waste stream, it is used as a bleaching agent in the production of coconut cream It is used as a reducing agent to break sulfide bonds in shrunken items of clothing made of natural fibers, thus allowing the garment to go back to its original shape after washing It is used as an SO2 source for the destruction of cyanide in commercial gold cyanidation processes. It is used in the gas industry as a corrosion inhibitor/oxygen scavenger, it is used in the water treatment industry to quench chlorine residual It is used in tint etching iron-based metal samples for microstructural analysis. When mixed with water, sodium metabisulfite releases sulfur dioxide, a pungent, unpleasant smelling gas that can cause breathing difficulties in some people.
For this reason, sodium metabisulfite has fallen from common use in recent times, with agents such as hydrogen peroxide becoming more popular for effective and odorless sterilization of equipment. Released sulfur dioxide however makes the water a strong reducing agent. Sodium metabisulfite releases sulfur dioxide in contact with strong acids: Na2S2O5 + 2 HCl → 2 NaCl + H2O + 2 SO2On heating to high temperature, it releases sulfur dioxide, leaving sodium sulfite behind: Na2S2O5 → Na2SO3 + SO2 Potassium metabisulfite International Chemical Safety Card 1461 The elusive crystal structure of sodium metabisulfite CDC - NIOSH Pocket Guide to Chemical Hazards
A fungus is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separate from the other eukaryotic life kingdoms of plants and animals. A characteristic that places fungi in a different kingdom from plants and some protists is chitin in their cell walls. Similar to animals, fungi are heterotrophs. Fungi do not photosynthesize. Growth is their means of mobility, except for spores, which may travel through the water. Fungi are the principal decomposers in ecological systems; these and other differences place fungi in a single group of related organisms, named the Eumycota, which share a common ancestor, an interpretation, strongly supported by molecular phylogenetics. This fungal group oomycetes; the discipline of biology devoted to the study of fungi is known as mycology. In the past, mycology was regarded as a branch of botany, although it is now known fungi are genetically more related to animals than to plants.
Abundant worldwide, most fungi are inconspicuous because of the small size of their structures, their cryptic lifestyles in soil or on dead matter. Fungi include symbionts of plants, animals, or other fungi and parasites, they may become noticeable when fruiting, either as molds. Fungi perform an essential role in the decomposition of organic matter and have fundamental roles in nutrient cycling and exchange in the environment, they have long been used in the form of mushrooms and truffles. Since the 1940s, fungi have been used for the production of antibiotics, more various enzymes produced by fungi are used industrially and in detergents. Fungi are used as biological pesticides to control weeds, plant diseases and insect pests. Many species produce bioactive compounds called mycotoxins, such as alkaloids and polyketides, that are toxic to animals including humans; the fruiting structures of a few species contain psychotropic compounds and are consumed recreationally or in traditional spiritual ceremonies.
Fungi can break down manufactured materials and buildings, become significant pathogens of humans and other animals. Losses of crops due to fungal diseases or food spoilage can have a large impact on human food supplies and local economies; the fungus kingdom encompasses an enormous diversity of taxa with varied ecologies, life cycle strategies, morphologies ranging from unicellular aquatic chytrids to large mushrooms. However, little is known of the true biodiversity of Kingdom Fungi, estimated at 2.2 million to 3.8 million species. Of these, only about 120,000 have been described, with over 8,000 species known to be detrimental to plants and at least 300 that can be pathogenic to humans. Since the pioneering 18th and 19th century taxonomical works of Carl Linnaeus, Christian Hendrik Persoon, Elias Magnus Fries, fungi have been classified according to their morphology or physiology. Advances in molecular genetics have opened the way for DNA analysis to be incorporated into taxonomy, which has sometimes challenged the historical groupings based on morphology and other traits.
Phylogenetic studies published in the last decade have helped reshape the classification within Kingdom Fungi, divided into one subkingdom, seven phyla, ten subphyla. The English word fungus is directly adopted from the Latin fungus, used in the writings of Horace and Pliny; this in turn is derived from the Greek word sphongos, which refers to the macroscopic structures and morphology of mushrooms and molds. The word mycology is derived from the Greek logos, it denotes the scientific study of fungi. The Latin adjectival form of "mycology" appeared as early as 1796 in a book on the subject by Christiaan Hendrik Persoon; the word appeared in English as early as 1824 in a book by Robert Kaye Greville. In 1836 the English naturalist Miles Joseph Berkeley's publication The English Flora of Sir James Edward Smith, Vol. 5. Refers to mycology as the study of fungi. A group of all the fungi present in a particular area or geographic region is known as mycobiota, e.g. "the mycobiota of Ireland". Before the introduction of molecular methods for phylogenetic analysis, taxonomists considered fungi to be members of the plant kingdom because of similarities in lifestyle: both fungi and plants are immobile, have similarities in general morphology and growth habitat.
Like plants, fungi grow in soil and, in the case of mushrooms, form conspicuous fruit bodies, which sometimes resemble plants such as mosses. The fungi are now considered a separate kingdom, distinct from both plants and animals, from which they appear to have diverged around one billion years ago; some morphological and genetic features are shared with other organisms, while others are unique to the fungi separating them from the other kingdoms: Shared features: With other euka
Sterilization refers to any process that eliminates, kills, or deactivates all forms of life and other biological agents present in a specified region, such as a surface, a volume of fluid, medication, or in a compound such as biological culture media. Sterilization can be achieved through various means, including: heat, irradiation, high pressure, filtration. Sterilization is distinct from disinfection and pasteurization, in that sterilization kills, deactivates, or eliminates all forms of life and other biological agents which are present. One of the first steps toward sterilization was made by Nicolas Appert who discovered that thorough application of heat over a suitable period slowed the decay of foods and various liquids, preserving them for safe consumption for a longer time than was typical. Canning of foods has helped to reduce food borne illness. Other methods of sterilizing foods include high pressure. In general, surgical instruments and medications that enter an aseptic part of the body must be sterile.
Examples of such instruments include scalpels, hypodermic needles, artificial pacemakers. This is essential in the manufacture of parenteral pharmaceuticals. Preparation of injectable medications and intravenous solutions for fluid replacement therapy requires not only sterility but well-designed containers to prevent entry of adventitious agents after initial product sterilization. Most medical and surgical devices used in healthcare facilities are made of materials that are able to go under steam sterilization. However, since 1950, there has been an increase in medical devices and instruments made of materials that require low-temperature sterilization. Ethylene oxide gas has been used since the 1950s for heat- and moisture-sensitive medical devices. Within the past 15 years, a number of new, low-temperature sterilization systems have been developed and are being used to sterilize medical devices. Steam sterilization is the most used and the most dependable. Steam sterilization is nontoxic, inexpensive microbicidal and heats and penetrates fabrics.
There are strict international rules to protect the contamination of Solar System bodies from biological material from Earth. Standards vary depending on both the type of its destination. Many components of instruments used on spacecraft cannot withstand high temperatures, so techniques not requiring excessive temperatures are used as tolerated, including heating to at least 120 °C, chemical sterilization, oxidization and irradiation; the aim of sterilization is the reduction of present microorganisms or other potential pathogens. The degree of sterilization is expressed by multiples of the decimal reduction time, or D-value, denoting the time needed to reduce the initial number N 0 to one tenth of its original value; the number of microorganisms N after sterilization time t is given by: N N 0 = 10. The D-value is a function of sterilization conditions and varies with the type of microorganism, water activity, pH etc.. For steam sterilization the temperature, in degrees Celsius, is given as an index.
Theoretically, the likelihood of the survival of an individual microorganism is never zero. To compensate for this, the overkill method is used. Using the overkill method, sterilization is performed by sterilizing for longer than is required to kill the bioburden present on or in the item being sterilized; this provides a sterility assurance level equal to the probability of a non-sterile unit. For high-risk applications, such as medical devices and injections, a sterility assurance level of at least 10−6 is required by the United States Food and Drug Administration. A used method for heat sterilization is the autoclave, sometimes called a converter or steam sterilizer. Autoclaves use steam heated to 121–134 °C under pressure. To achieve sterility, the article is placed in a chamber and heated by injected steam until the article reaches a temperature and time setpoint. All the air is removed from the chamber, because air is undesired in the moist heat sterilization process; the article is held at the temperature setpoint for a period of time which varies depending on what bioburden is present on the article being sterilized and its resistance to steam sterilization.
A general cycle would be anywhere between 3 and 15 minutes, at 121 °C at 100 kPa, sufficient to provide a sterility assurance level of 10−4 for a product with a bioburden of 106 and a D-value of 2.0 minutes. Following sterilization, liquids in a pressurized autoclave must be cooled to avoid boiling over when the pressure is released; this may be achieved by depressurizing the sterilization chamber and allowing liqui