1.
Settling
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Settling is the process by which particulates settle to the bottom of a liquid and form a sediment. Particles that experience a force, either due to gravity or due to centrifugal motion will tend to move in a manner in the direction exerted by that force. For gravity settling, this means that the particles tend to fall to the bottom of the vessel. Settling is an important operation in many applications, such as mining, wastewater treatment, biological science, space propellant reignition, for settling particles that are considered individually, i. e. dilute particle solutions, there are two main forces enacting upon any particle. The primary force is a force, such as gravity. The applied force is not affected by the particles velocity. For a particle at rest no drag force will be exhibited, as the particle increases in velocity eventually the drag force and the applied force will approximately equate, causing no further change in the particles velocity. This velocity is known as the velocity, settling velocity or fall velocity of the particle. This is readily measurable by examining the rate of fall of individual particles, the terminal velocity of the particle is affected by many parameters, i. e. anything that will alter the particles drag. Hence the terminal velocity is most notably dependent upon grain size, for dilute suspensions, Stokes law predicts the settling velocity of small spheres in fluid, either air or water. This originates due to the strength of forces at the surface of the particle providing the majority of the retarding force. Stokes law applies when the Reynolds number, Re, of the particle is less than 0.1. Experimentally Stokes law is found to hold within 1% for R e ≤0.1, within 3% for R e ≤0.5 and within 9% R e ≤1.0. With increasing Reynolds numbers, Stokes law begins to break due to the increasing importance of fluid inertia. In this region the inertia of the fluid is responsible for the majority of force transfer to the particle. This constant value implies that the efficiency of transfer of energy from the fluid to the particle is not a function of fluid velocity. As such the terminal velocity of a particle in a Newtonian regime can again be obtained by equating the drag force to the applied force, resulting in the following expression w =2.4612. In the intermediate region between Stokes drag and Newtonian drag, there exists a regime, where the analytical solution to the problem of a falling sphere becomes problematic
2.
Sedimentation
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Sedimentation is the tendency for particles in suspension to settle out of the fluid in which they are entrained and come to rest against a barrier. This is due to their motion through the fluid in response to the acting on them. In geology, sedimentation is often used as the opposite of erosion, in that sense, it includes the termination of transport by saltation or true bedload transport. Settling is the falling of suspended particles through the liquid, whereas sedimentation is the termination of the settling process, in estuarine environments, settling can be influenced by the presence or absence of vegetation. Trees such as mangroves are crucial to the attenuation of waves or currents, even small molecules supply a sufficiently strong force to produce significant sedimentation. This process is used in the biotech industry to separate cells from the culture media. In a sedimentation experiment, the applied force accelerates the particles to a velocity v t e r m at which the applied force is exactly canceled by an opposing drag force. For small enough particles, the force varies linearly with the terminal velocity, i. e. F d r a g = f v t e r m where f depends only on the properties of the particle. Thus, measuring s can reveal underlying properties of the particle, in many cases, the motion of the particles is blocked by a hard boundary, the resulting accumulation of particles at the boundary is called a sediment. The concentration of particles at the boundary is opposed by the diffusion of the particles, the sedimentation of a single particle under gravity is described by the Mason–Weaver equation, which has a simple exact solution. The sedimentation coefficient s in this case equals m b / f, the sedimentation of a single particle under centrifugal force is described by the Lamm equation, which likewise has an exact solution. The sedimentation coefficient s also equals m b / f, where m b is the buoyant mass, the Lamm equation also has extra terms, since it pertains to sector-shaped cells, whereas the Mason–Weaver equation is one-dimensional. They settle as individual particles and do not flocculate or stick to other during settling, example, alum or iron coagulation Type 3 sedimentation is also known as zone sedimentation. In this process the particles are at a high concentration such that the particles tend to settle as a mass, zone settling occurs in lime-softening, sedimentation, active sludge sedimentation and sludge thickeners. In geology, sedimentation is the deposition of particles carried by a fluid flow, for suspended load, this can be expressed mathematically by the Exner equation, and results in the formation of depositional landforms and the rocks that constitute sedimentary record. An undesired increased transport and sedimentation of suspended material is called siltation, high sedimentation rates can be a result of poor land management and a high frequency of flooding events. If not managed properly, it can be detrimental to fragile ecosystems on the receiving end, climate change also affects siltation rates. In chemistry, sedimentation has been used to measure the size of large molecules, where the force of gravity is augmented with centrifugal force in an ultracentrifuge
3.
Laboratory centrifuge
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A laboratory centrifuge is a piece of laboratory equipment, driven by a motor, which spins liquid samples at high speed. There are various types of centrifuges, depending on the size, like all other centrifuges, laboratory centrifuges work by the sedimentation principle, where the centripetal acceleration is used to separate substances of greater and lesser density. There are different providers of laboratory centrifuges like Eppendorf, Thermo-Heraeus, Thermo-Sorvall, Hettich, Beckmann-Coulter, MSE, Sigma, centrifuge tubes are precision-made, high-strength tubes of glass or plastic made to fit exactly in rotor cavities. They may vary in capacity from 50 mL down to much smaller capacities used in microcentrifuges used extensively in biology laboratories. They can be cleaned like other laboratory glassware, and can be sterilized by autoclaving and they must be handled with care, since small scratches can cause failure under the strong forces imposed during a run. Glass tubes are inserted into soft rubber sleeves to cushion them during runs, plastic centrifuge tubes, especially tend to be less expensive and, with care, can be just as durable as glass. Water is preferred when plastic centrifuge tubes are used and they are more difficult to clean thoroughly, and are usually inexpensive enough to be considered disposable. Disposable plastic microlitre tubes of 0. 5ml to 2ml are commonly used in microcentrifuges and they are molded from a flexible transparent plastic similar to polythene, are semi-conical in shape, with integral, hinged sealing caps. Larger samples are spun using centrifuge bottles, which range in capacity from 250 to 1000 millilitres, although some are made of heavy glass, centrifuge bottles are usually made of shatterproof plastics such as polypropylene or polycarbonate. Sealing closures may be used for added leak-proof assurance, the load in a laboratory centrifuge must be carefully balanced. This is achieved by using a combination of samples and balance tubes which all have the weight or by using various balancing patterns without balance tubes. Small differences in mass of the load can result in a force imbalance when the rotor is at high speed. This force imbalance strains the spindle and may result in damage to the centrifuge or personal injury, some centrifuges have an automatic rotor imbalance detection feature that immediately discontinues the run when an imbalance is detected. Before starting a centrifuge, a check of the rotor. Centrifuge rotors should never be touched while moving, because a spinning rotor can cause serious injury, modern centrifuges generally have features that prevent accidental contact with a moving rotor as the main lid is locked during the run. Centrifuge rotors have tremendous kinetic energy during high speed rotation, rotor failure, caused by mechanical stress from the high forces imparted by the motor, can occur due to manufacturing defects, routine wear and tear, or improper use and maintenance. Such a failure can be catastrophic failure, especially with larger centrifuges, uncontained rotor failures have shattered laboratory windows and destroyed refrigerators and cabinetry. Another potential hazard is the aerosolization of hazardous samples during centrifugation, to prevent contamination of the laboratory, rotor lids with special aerosol-tight gaskets are available
4.
History of chemistry
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The history of alchemy represents a time span from ancient history to the present. By 1000 BC, civilizations used technologies that would form the basis of the various branches of chemistry. The protoscience of chemistry, alchemy, was unsuccessful in explaining the nature of matter, however, by performing experiments and recording the results, alchemists set the stage for modern chemistry. The distinction began to emerge when a clear differentiation was made between chemistry and alchemy by Robert Boyle in his work The Sceptical Chymist, while both alchemy and chemistry are concerned with matter and its transformations, chemists are seen as applying scientific method to their work. The history of chemistry is intertwined with the history of thermodynamics, the earliest recorded metal employed by humans seems to be gold which can be found free or native. Small amounts of gold have been found in Spanish caves used during the late Paleolithic period. Silver, copper, tin and meteoric iron can also be found native, egyptian weapons made from meteoric iron in about 3000 BC were highly prized as Daggers from Heaven. Arguably the first chemical reaction used in a manner was fire. However, for fire was seen simply as a mystical force that could transform one substance into another while producing heat. Fire affected many aspects of early societies and these ranged from the simplest facets of everyday life, such as cooking and habitat lighting, to more advanced technologies, such as pottery, bricks, and melting of metals to make tools. It was fire that led to the discovery of glass and the purification of metals which in turn gave way to the rise of metallurgy. During the early stages of metallurgy, methods of purification of metals were sought, certain metals can be recovered from their ores by simply heating the rocks in a fire, notably tin, lead and copper, a process known as smelting. The first evidence of this extractive metallurgy dates from the 5th and 6th millennium BC, to date, the earliest copper smelting is found at the Belovode site, these examples include a copper axe from 5500 BC belonging to the Vinča culture. Other signs of early metals are found from the third millennium BC in places like Palmela, Los Millares, however, as often happens with the study of prehistoric times, the ultimate beginnings cannot be clearly defined and new discoveries are continuous and ongoing. These first metals were single ones or as found, by combining copper and tin, a superior metal could be made, an alloy called bronze, a major technological shift which began the Bronze Age about 3500 BC. These naturally occurring ores typically included arsenic as a common impurity, copper/tin ores are rare, as reflected in the fact that there were no tin bronzes in western Asia before 3000 BC. After the Bronze Age, the history of metallurgy was marked by armies seeking better weaponry, countries in Eurasia prospered when they made the superior alloys, which, in turn, made better armor and better weapons. This often determined the outcomes of battles, significant progress in metallurgy and alchemy was made in ancient India
5.
Cellulose
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Cellulose is an organic compound with the formula n, a polysaccharide consisting of a linear chain of several hundred to many thousands of β linked D-glucose units. Cellulose is an important structural component of the cell wall of green plants, many forms of algae. Some species of bacteria secrete it to form biofilms, Cellulose is the most abundant organic polymer on Earth. The cellulose content of cotton fiber is 90%, that of wood is 40–50%, Cellulose is mainly used to produce paperboard and paper. Smaller quantities are converted into a variety of derivative products such as cellophane. Conversion of cellulose from energy crops into biofuels such as ethanol is under investigation as an alternative fuel source. Cellulose for industrial use is mainly obtained from wood pulp and cotton, some animals, particularly ruminants and termites, can digest cellulose with the help of symbiotic micro-organisms that live in their guts, such as Trichonympha. In humans, cellulose acts as a bulking agent for feces and is often referred to as a dietary fiber. Cellulose was discovered in 1838 by the French chemist Anselme Payen, Cellulose was used to produce the first successful thermoplastic polymer, celluloid, by Hyatt Manufacturing Company in 1870. Production of rayon from cellulose began in the 1890s and cellophane was invented in 1912, hermann Staudinger determined the polymer structure of cellulose in 1920. The compound was first chemically synthesized in 1992, by Kobayashi, Cellulose has no taste, is odorless, is hydrophilic with the contact angle of 20–30 degrees, is insoluble in water and most organic solvents, is chiral and is biodegradable. It was shown to melt at 467 °C in 2016 and it can be broken down chemically into its glucose units by treating it with concentrated mineral acids at high temperature. Cellulose is derived from D-glucose units, which condense through β-glycosidic bonds and this linkage motif contrasts with that for α-glycosidic bonds present in starch and glycogen. This confers tensile strength in cell walls, where cellulose microfibrils are meshed into a polysaccharide matrix, compared to starch, cellulose is also much more crystalline. Whereas starch undergoes a crystalline to amorphous transition when heated beyond 60–70 °C in water, cellulose requires a temperature of 320 °C, several different crystalline structures of cellulose are known, corresponding to the location of hydrogen bonds between and within strands. Natural cellulose is cellulose I, with structures Iα and Iβ, Cellulose produced by bacteria and algae is enriched in Iα while cellulose of higher plants consists mainly of Iβ. Cellulose in regenerated cellulose fibers is cellulose II, the conversion of cellulose I to cellulose II is irreversible, suggesting that cellulose I is metastable and cellulose II is stable. With various chemical treatments it is possible to produce the structures cellulose III, many properties of cellulose depend on its chain length or degree of polymerization, the number of glucose units that make up one polymer molecule
6.
Solubility
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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
7.
Supersaturation
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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
