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A solution forms when a solute dissolves in a solvent. The concentration of a solution is a measure of the amount of solid dissolved in 1 dm³ of solution. When the mass of solute dissolved is measured in g, the units for concentration are g/dm³.

Volume units

Apparatus used to measure volumes is usually marked in cm³ or ml. Although these are different units, they describe the same volume. For example, 250 ml = 250 cm³.

Volumes used in concentration calculations must be in dm³, not in cm³ or ml. It is useful to know that 1 dm³ = 1,000 cm³. This means:

• divide by 1,000 to convert from cm³ to dm³
• multiply by 1,000 to convert from dm³ to cm³

For example, 250 cm³ is 0.25 dm³ (250/1,000). It is often easiest to convert from cm³ to dm³ before continuing with a concentration calculation.