Concentration

Summary: The amount of solute dissolved per unit volume of solution. Usually expressed in mol/dm³ or g/dm³. Tags: igcse chemistry definition stoichiometry Created: 2026-07-14 Last Updated: 2026-07-14

Concentration is a quantitative measure of the amount of solute dissolved in a specific volume of solvent or solution, and it is one of the most fundamental concepts in quantitative chemistry. In IGCSE, concentration is expressed in two ways: mass concentration in grams per cubic decimetre (g/dm³), calculated by dividing the mass of solute in grams by the volume of solution in dm³; and molar concentration in moles per cubic decimetre (mol/dm³), calculated by dividing the amount of solute in moles by the volume of solution in dm³. These two measures are interconverted using the formula concentration (mol/dm³) = concentration (g/dm³) / molar mass (g/mol), a calculation that appears frequently in IGCSE titration problems and stoichiometry questions. According to collision theory, a higher concentration means more dissolved particles per unit volume, which results in a greater frequency of successful collisions between reactant particles and therefore a faster rate of reaction — this is why changing concentration is one of the standard methods of investigating reaction rates in the IGCSE laboratory, alongside changing temperature, surface area, and the use of catalysts. In the exam, students must be able to calculate concentration in both units, convert between them using molar mass, and apply their understanding to explain rate experiments, prepare solutions, and solve titration problems such as finding the unknown concentration of an acid.

Key term — IGCSE Chemistry (0620/0971) glossary.