1(e) Chemical formulae, equations and calculations Glossary

Relative atomic mass

Weighted average mass of an atom of an element relative to the mass of an atom of carbon-12

Relative formula mass

The sum of the relative atomic masses of the elements as given in the formula.

Moles

Mass / Mr

Concentration

moles/volume

Mass

moles x Mr

Molar volume

the volume occupied by 1 mole of gas (24dm^3 at room temperature and pressure)

Empirical formula

Gives the simplest whole number ratio of the atoms present in a compound

Molecular formula

Shows the actual number of each type of atom present in a molecule (covalent compound) or formula unit (ionic compound)

Hydrated

A crystalline compound containing water molecules

Water of crystallisation

Water chemically bonded within a crystal structure

Anhydrous

without water

Combustion reaction

Reaction in which a substance reacts with oxygen to form products and heat

Limiting reagent

the reactant that determines the amount of product that can be formed in a reaction

Excess

having more than enough of a reactant to react with all of something else

Actual yield

the measured amount of a product obtained from a reaction

Theoretical yield

the maximum amount of product that can be produced from a given amount of reactant

Percentage yield

actual yield/theoretical yield x 100

Thermal decomposition

The breakdown of a compound by heat

Titration

A solution of known concentration is used to determine the concentration of another solution

Avogadro's constant

Number of Carbon-12 atoms in 12g of Carbon-12 = 6.022 x 10^23 = 1 mole

Conservation of mass

mass cannot be created or destroyed

Avogadro's Gas Law

equal volumes of all gases, at the same temperature and pressure, have the same number of molecules

Volume

moles/concentration

Molar mass

the mass of 1 mole of a substance