Cameroon GCE O-Level Chemistry flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Diffusion

The net spreading of particles from a region of higher concentration to lower concentration due to their random motion; lighter particles diffuse faster than heavier ones at the same temperature.

Brownian motion

The random jiggling of small visible particles suspended in a fluid, caused by unequal collisions with the much smaller, invisible fluid molecules; it provides evidence that matter is particulate.

Boyle's law

At constant temperature, the pressure of a fixed mass of gas is inversely proportional to its volume, so p1V1 = p2V2. Doubling the pressure halves the volume.

Charles's law

At constant pressure, the volume of a fixed mass of gas is directly proportional to its absolute temperature in kelvin, so V1/T1 = V2/T2.

Isotopes

Atoms of the same element with the same number of protons but different numbers of neutrons. They have identical chemical properties but different masses and physical behaviour.

Relative atomic mass

The weighted mean mass of the atoms of an element compared with one-twelfth the mass of a carbon-12 atom, taking natural isotopic abundances into account.

Ionic bond

The strong electrostatic attraction between oppositely charged ions, formed when a metal transfers one or more electrons to a non-metal, producing a giant ionic lattice.

Metallic bond

The attraction between a lattice of positive metal ions and a sea of delocalised outer electrons, which explains electrical conductivity, malleability and ductility of metals.

Mole

The amount of substance containing 6.02 × 10²³ specified particles; its mass in grams equals the relative atomic or molecular mass of the substance.

Empirical formula

The simplest whole-number ratio of atoms of each element in a compound, found by dividing each element's mole ratio by the smallest value obtained.

Limiting reactant

The reactant that is completely used up first in a reaction, determined by dividing the moles of each reactant by its coefficient; it fixes the maximum possible yield.

Titration

A volumetric technique in which a solution of known concentration is added from a burette to a measured volume of another solution until the indicator shows the end point.

Strong acid

An acid that ionises completely in water, such as hydrochloric, nitric or sulfuric acid, producing a high concentration of hydrogen ions and a low pH.

Exothermic reaction

A reaction that releases energy to the surroundings, usually as heat, so the temperature rises and the enthalpy change is negative; combustion and neutralisation are examples.

Activation energy

The minimum energy colliding particles must have for a reaction to occur; catalysts lower it, increasing the proportion of successful collisions and hence the rate.

Le Chatelier's principle

When a system at equilibrium is disturbed by a change in concentration, pressure or temperature, it shifts in the direction that opposes the change.

Electrolysis

The decomposition of an ionic compound, molten or in aqueous solution, by passing a direct electric current through it using inert or reactive electrodes.

Oxidation

The loss of electrons by a species, or the gain of oxygen, or the loss of hydrogen; it always occurs together with reduction in a redox reaction.

Oxidising agent

A species that accepts electrons from another substance, causing that substance to be oxidised while the oxidising agent itself is reduced.

Reactivity series

A ranking of metals by how readily they lose electrons and react; potassium is most reactive, gold least, and metals above carbon are extracted by electrolysis.

Galvanising

Coating iron or steel with a layer of zinc, which prevents rusting by excluding water and oxygen and by acting as a sacrificial metal if the coating is scratched.

Thermal decomposition

The breakdown of a compound by heating alone, for example a metal carbonate forming the metal oxide and carbon dioxide; stability increases with metal reactivity.

Alkene

An unsaturated hydrocarbon containing at least one carbon–carbon double bond, with general formula CₙH₂ₙ; it decolourises bromine water and undergoes addition reactions.

Cracking

The breaking of long-chain hydrocarbons into shorter, more useful alkanes and alkenes by heating with a catalyst, increasing petrol supply and providing monomers for polymers.

Fermentation

The conversion of glucose to ethanol and carbon dioxide by yeast enzymes at about 30–35 °C in the absence of air; it stops when ethanol reaches roughly 15%.

Esterification

The reaction of a carboxylic acid with an alcohol in the presence of a little concentrated sulfuric acid catalyst, producing an ester with a characteristic sweet smell and water.

Flame test colours

Lithium gives crimson, sodium yellow, potassium lilac, calcium brick-red and copper blue-green; the wire is cleaned in concentrated hydrochloric acid between tests.

Test for sulfate

Acidify the solution with dilute hydrochloric acid, then add barium chloride solution; a white precipitate of barium sulfate confirms the presence of sulfate ions.

Chromatography Rf value

The ratio of the distance travelled by a spot to the distance travelled by the solvent front; the more soluble component travels further and has the larger Rf.

Heating to constant mass

Repeatedly heating, cooling and weighing a solid until two successive masses agree, used to remove all water of crystallisation or ensure complete reaction.

Diluting concentrated sulfuric acid

Add the acid slowly to water with stirring, never water to acid; the mixture becomes very hot and adding water to acid can cause violent spattering.

Fume cupboard use

A ventilated enclosure used when handling toxic or volatile substances such as chlorine, bromine or concentrated acids, preventing inhalation of harmful vapours.