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The concentration of a solution can be measured in g/dm³ or in mol/dm³.

Volume units

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

1. divide by 1,000 to convert from cm³ to dm³
2. multiply by 1,000 to convert from dm³ to cm³

For example, 500 cm³ is 0.5 dm³ (500 ÷ 1,000). It is often easiest to convert from cm³ to dm³ before continuing with a concentration calculation.

Converting between units

The relative formula mass, M_r, of the solute is used to convert between mol/dm³ and g/dm³:

To convert from mol/dm³ to g/dm³, multiply by the M_r.

Example

Calculate the concentration of 0.100 mol/dm³ sodium hydroxide solution in g/dm³. (Relative formula mass: NaOH = 40.0)

concentration = 0.100 × 40.0

= 4.00 g/dm³