General Science - Chemistry (Important glossary to remember)-2

General Science - Chemistry (Important glossary to remember):

AerosolA colloid in which solid particles or liquid droplets are suspended in a gas. Smoke is an example of a solid aerosol; fog is an example of a liquid aerosol.

AbrasiveA very hard, brittle, heat-resistant substance that is used to grind the edges or rough surfaces of an object. boron carbide, diamond, and corundum are abrasives.

AcidulantA substance added to food or beverages to lower pH and to impart a tart, acid taste. Phosphoric acid is an acidulant added to cola drinks.

Activated charcoalA porous form of carbon that acts as a powerful adsorbent , used to decolorize liquids, recover solvents, and remove toxins from water and air.

AlkaloidA class of bitter-tasting, basic organic compounds with nitrogen-containing rings. Alkaloids often have powerful effects on living things. Examples are cocaine, nicotine, strychnine, caffeine, and morphine

AllotropeSome elements occur in several distinct forms called allotropes. Allotropes have different chemical and physical properties. For example, graphite and diamond are allotropes of carbon.

AntichlorA chemical compound that reacts with chlorine-based bleaches to stop the bleaching. Thiosulfate compounds are antichlors.

AntioxidantAntioxidants are compounds that slow oxidation processes that degrade foods, fuels, rubber, plastic, and other materials. Antioxidants like butylated hydroxyanisole (BHA) are added to food to prevent fats from becoming rancid and to minimize decomposition of vitamins and essential fatty acids; they work by scavenging destructive free radicals from the food.

Free radicalA free radical is a molecule with an odd number of electrons. Free radicals do not have a completed octet and often undergo vigorous redox reactions. Free radicals produced within cells can react with membranes, enzymes, and genetic material, damaging or even killing the cell. Free radicals have been implicated in a number of degenerative conditions, from natural aging to Alzheimers disease

Avogadro numberIt is formally defined to be the number of carbon-12 atoms in 12 grams (0.012 kg) of unbound carbon-12 in its rest-energy electronic state. The number of particles in one mole, equal to 6.02214199 × 10²³ mol-1 (± 0.00000047).

ColloidA colloid is a heterogeneous mixture composed of tiny particles suspended in another material. The particles are larger than molecules but less than 1 µm in diameter. Particles this small do not settle out and pass right through filter paper. Milk is an example of a colloid. The particles can be solid, tiny droplets of liquid, or tiny bubbles of gas; the suspending medium can be a solid, liquid, or gas (although gas-gas colloids are not possible).

Carotene.Carotene is an unsaturated hydrocarbon pigment found in many plants It is responsible for the orange colour of the carrot. Carotene is the basic building block of vitamin A.

CaffeineA substance found in tea, coffee, and cola that acts as a stimulant. It is extremely soluble in supercritical fluid carbon dioxide and somewhat soluble in water; aqueous solutions of caffeine quickly break down.

BufferA solution that can maintain its pH value with little change when acids or bases are added to it. Buffer solutions are usually prepared as mixtures of a weak acid with its own salt or mixtures of salts of weak acids. For example, a 50:50 mixture of 1 M acetic acid and 1 M sodium acetate buffers pH around 4.7.

DiamondA crystalline form of carbon, made of a network of covalent, tetrahedrally bound carbon atoms.

DeliquescentDeliquescent compounds absorb so much moisture from the air that they dissolve. Examples are calcium chloride and sodium hydroxide

Dry cell or Leclanché cellA electrolytic cell that uses a moist paste rather than a liquid as an electrolyte. Flashlight batteries are dry cells with a zinc cup for an anode, a carbon rod for a cathode, and a paste made of powdered carbon, NH₄Cl, ZnCl₂, and MnO₂ for an electrolyte.

DistillationDistillation 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 alcoholA 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

EmulsionA colloid formed from tiny liquid droplets suspended in another, immiscible liquid. Milk is an example of an emulsion

Fractional distillationA 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.

EfflorescentEfflorescent 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.

EsterAn 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

GelA 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

FoamA 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 osmosisSolvent 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.

IsomersIsomers have identical molecular formulas but different structural formulas

HygroscopicAble 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.

EndothermicA 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.

ExothermicA 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.