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General Science - Chemistry (Important glossary to remember)

Written By STPORTAL on Sunday, March 18, 2012 | 2:47 PM


General Science - Chemistry (Important glossary to remember):
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Distillation
Distillation is a technique for separating components of a mixture on the basis of differing boiling points. The mixture is heated, vaporizing some of the components. The vapor is collected and condensed to isolate the components with the lowest boiling points.
Ethanol. (CH3CH2OH) ethyl alcohol; grain alcohol
A colorless, flammable liquid produced by fermentation of sugars. Ethanol is the alcohol found in alcoholic beverages. Ethyl alcohol is used as a solvent, extractant, antifreeze, intermediate in the synthesis of innumerable organic chemicals and as a fuel and gasoline additive
Emulsion
A colloid formed from tiny liquid droplets suspended in another, immiscible liquid. Milk is an example of an emulsion
Fractional distillation
A technique for separation of liquid mixtures by distillation that uses a tower attached to a flask containing the mixture to perform multiple distillations. Vapor moving up the column condenses on packing material inside the column, trickles down the column, and again vaporises. The more volatile component can then be drawn off at the top of the component, while the less volatile component remains at the bottom.
Ketone.
An organic compound that contains a carbonyl group. For example, methyl ethyl ketone is CH3COCH2CH3 is used in some adhesives.
Efflorescent
Efflorescent substances lose water of crystallization to the air. The loss of water changes the crystal structure, often producing a powdery crust. The thermodynamic requirement for efflorescence is that the partial pressure of water vapor at the surface of the solid (its dissociation pressure) exceed the partial pressure of water vapor in the air. A typical efflorescent substance is Glaubers salt, Na2SO4 · 10H2O. The spontaneous loss of water normally requires that the crystal structure be rearranged, and consequently, efflorescent salts usually go to microcrystalline powders when they lose their water of hydration.
Ester
An ester is a compound formed from an acid and an alcohol. In esters of carboxylic acids, the -COOH group and the -OH group lose water and become a -COO- linkage
Gel
A gell is a sol in which the solid particles fuse or entangle to produce a rigid or semirigid mixture. For example, gelatin dissolved in water produces a sol of protein molecules. When the gelatin is cooked, the protein chains entangle and crosslink, forming a gel which is a mesh of solid protein with trapped pockets of liquid inside. Fruit jellies are also gels
Foam
A colloid in which bubbles of gas are suspended in a solid or liquid. Aerogel (solid smoke) and Styrafoam are examples of solid foams; whipped cream is an example of a liquid foam
Reverse osmosis
Solvent molecules flow spontaneously from a dilute solution through a semipermeable membrane to a more concentrated solution (osmosis). In reverse osmosis, pressure is applied to the more concentrated solution to force the flow of solvent to go from more concentrated to more dilute solution. Reverse osmosis is used to produce fresh water from sea water.
Isomers
Isomers have identical molecular formulas but different structural formulas
Hygroscopic
Able to absorb moisture from air. For example, sodium hydroxide pellets are so hygroscopic that they dissolve in the water they absorb from the air.
Hydrazine.
A colorless, fuming, corrosive liquid that is a powerful reducing agent. It is used in jet and rocket fuels, and as an intermediate in the manufacture of agricultural, textile, photographic, and industrial chemicals.
Endothermic
A process that absorbs heat. The enthalpy change for an endothermic process has a positive sign. Some examples of endothermic processes are
Cooking food,Melting of ice,Depressurising a pressure can
The mixing of barium hydroxide and ammonium thiocyanate causes a powerful endothermic reaction that causes the products to become so cold that the moisture from the air forms a layer of frost on the outer surface of the beaker.
Endothermic substances, both natural, e.g. gypsum, and synthetic, e.g. resin-based intumescents, are popular for use in heatshielding, ablation, materials in space physics, fireproofing, e.g. fire-resistive coatings for LPG vessels, and compartmentalisation of fire in buildings, which is the cornerstone of passive fire protection. Typically, the technological basis is the conversion of hydrates, or chemically bound water into vapour, or steam.
Exothermic
A process that releases heat. The enthalpy change for an exothermic process is negative. Examples of exothermic processes are
·         combustion reactions, freezing of water, respiration and neutralization reactions .
·         Adding concentrated acid to water
·         Adding water to anhydrous copper(II) sulfate
·         The reaction taking place with Thermite(fire-hazardous mixture of ferric oxide and powdered aluminum; upon ignition by a magnesium ribbon, it reaches a temperature of 4000°F (2200°C), sufficient to soften steel; used for industrial purposes or as an incendiary bomb.
·         Reactions taking place in a self-heating can based on lime and aluminum.
Sol
A colloid with solid particles suspended in a liquid. Examples are protoplasm, starch in water, and gels.
Tyndall effect
Light passing through a colloid is scattered by suspended particles. The light beam becomes clearly visible; this phenomenon is called the Tyndall effect. For example, car headlight beams can be seen in fog, but the beams are invisible in clear air.

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