Topic 3 Stoichiometry

Relative atomic mass Ar

Weighted average mass of an atom compared to carbon 12

Relative molecular mass Mr

Sum of relative atomic masses in molecule

Mole

Amount of substance containing Avogadro number of particles

Avogadro constant

6.02 × 10^23 particles per mole

Formula for moles

n=\frac{m}{M_r}

Moles from concentration and volume

n=cV

Concentration

Amount of solute dissolved per dm cubed of solution

Concentration formula

c=\frac{n}{V}

Percentage composition

Percentage by mass of each element in compound

Limiting reactant

Reactant completely used up first

Excess reactant

Reactant left over after reaction

Percentage yield

Actual yield divided by theoretical yield x 100

Atom economy

Useful product Mr divided by total Mr of products x 100

Gas volume at rtp

One mole of gas occupies 24 dm cubed at room temperature and pressure

Formula for gas moles

n=\frac{V}{24}

Hydrated substance

Substance chemically combined with water

Anhydrous substance

Substance containing no water

Water of crystallisation

Water molecules present in hydrated crystals

Empirical formula calculation

Use mole ratio of elements

Molecular formula calculation

Multiply empirical formula by factor from Mr

Titration

Method used to determine concentration of solution

Ionic equation

Equation showing only ions involved in reaction