Stoichiometry is the study of mole relationships involved in chemical reactions.

Chemical equations, using formulae and state symbols, can be written and balanced to show the mole ratio(s) of reactants and products, including multi-step reactions.

The mass of a mole of any substance, in grams ($g$), is equal to the gram formula mass ($GFM$) and can be calculated using relative atomic masses.

Calculations can be performed using the relationship between the mass and the number of moles of a substance.

For solutions, the mass of solute ($g$), the number of moles of solute ($mol$), the volume of solution ($l$), or the concentration of the solution ($mol \space l^{-1}$), can be calculated from data provided.

Percentage by mass is the mass of solute, in $g$, made up to $100$ $cm^3$ of solution.

Percentage by volume is the number of $cm^3$ of solute made up to $100$ $cm^3$ of solution.

The unit $ppm$ stands for parts per million and refers to $1 \space mg$ per $kg$ or $1$ $mg$ per $l$.

Calculations can be performed using data, including:

• GFM
• masses
• number of moles
• concentrations and volumes of solutions
• volumes of gases
• reactant excess
• theoretical and percentage yield
• empirical formulae

Theoretical yields can be calculated and compared with actual yields, leading to determining the percentage yield.

The percentage yield of a reaction is reduced by

• mass transfer or mechanical losses