OCR GCSE Chemistry B Key Terms

Precipitation with a low pH (typically below 5.5) caused by sulfur dioxide and nitrogen oxides dissolving in cloud water.

A diverse group of photosynthetic organisms that evolved after cyanobacteria and pioneered the oxygenation of the oceans and atmosphere, responsible for roughly 90% of early oxygen.

A thick suspension of an alkaline solid, such as limestone or lime, in water used to neutralise acidic gases.

A state symbol used to describe a substance that is dissolved in water.

Distinctive layers of sedimentary rock containing iron oxides that serve as geological evidence for when oxygen first appeared in the oceans and reacted with dissolved iron.

The specific temperature at which a substance changes from a liquid to a gas throughout the bulk of the liquid.

The physical action of forcing a gas through a liquid, essential for the carbon dioxide limewater test.

The macroscopic physical and chemical characteristics of a substance that emerge when multiple particles interact (e.g., melting point, conductivity).

A wooden splint that is actively flaming, used specifically for testing hydrogen. Also known as a lighted splint.

Rock types, such as limestone and marble, that are highly susceptible to chemical corrosion from acid rain.

A toxic gas produced during the incomplete combustion of hydrocarbon fuels.

A process where impurities like sulfur deposit on a catalyst's surface, blocking active sites and making it ineffective.

A device fitted to car exhausts that uses transition metals to convert toxic gases into less harmful gases through redox reactions.

Devices fitted to vehicle exhausts that reduce harmful emissions by catalysing reactions, such as reducing nitrogen monoxide to nitrogen gas and oxidising carbon monoxide.

A process where one or more new substances are formed by the breaking and making of chemical bonds, which is usually not easily reversed.

A representation of a substance using symbols for its constituent elements and subscripts to show the specific number of atoms in a molecule.

A one, two, or three-letter code used to represent an element on the Periodic Table, where the first letter is always uppercase.

A reaction environment where no substances (matter) can enter or leave, such as a sealed flask.

The visual description (alongside 'milky') used in mark schemes to describe the suspension of fine white solid particles in a liquid.

A multiplier placed in front of a chemical formula to balance the number of atoms, which multiplies every atom in that specific formula.

The physical change of state from a gas to a liquid as a substance loses internal energy.

The temperature at which a gas becomes a liquid, numerically identical to the boiling point for a pure substance.

The principle that mass is neither created nor destroyed during physical or chemical changes in a closed system.

A strong electrostatic force of attraction between a shared pair of electrons and the nuclei of the bonded atoms.

The first group of prokaryotic (single-celled) organisms to perform oxygenic photosynthesis.

A measure of how much mass is contained within a given volume of a substance.

The direct physical change of state from a gas to a solid.

Non-metal elements that exist naturally as pairs of atoms bonded together, such as $H_2$ and $O_2$.

A molecule consisting of exactly two atoms of the same or different elements chemically bonded together.

The collection of gases that surrounded the Earth during its first billion years, thought to be formed by intense volcanic activity.