Acid solutions can be dilute or concentrated. Concentration is calculated from mass of solute and volume of solvent. Acids may be weak or strong depending on how far the acid breaks up when dissolved.

The concentration of a solution can be calculated using:

- the mass of dissolved solute in grams (g)
- the volume of solution (or solvent) in cubic decimetres (dm
^{3})

The units for concentration can also be shown as g dm^{-3}, but this means the same as g/dm^{3}.

8 g of sodium hydroxide is dissolved in 2 dm^{3} of water. Calculate the concentration of the sodium hydroxide solution formed.

concentration =

concentration =

concentration = 4 g/dm^{3}

Apparatus used to measure volumes is usually marked in cm^{3} or ml. Although these are different units, they describe the same volume. For example, 250 ml = 250 cm^{3}.

Volumes used in concentration calculations must be in dm^{3}, not in cm^{3} or ml. It is useful to know that 1 dm^{3} = 1,000 cm^{3}. This means:

- divide by 1,000 to convert from cm
^{3}to dm^{3} - multiply by 1,000 to convert from dm
^{3}to cm^{3}

For example, 250 cm^{3} is 0.25 dm^{3} (250 ÷ 1,000). It is often easiest to convert from cm^{3} to dm^{3} before continuing with a concentration calculation.

- Question
100 cm

^{3}of dilute hydrochloric acid contains 0.5 g of dissolved hydrogen chloride. Calculate the concentration of the acid in g/dm^{3}.volume of acid = 100 ÷ 1,000 = 0.1 dm

^{3}concentration of acid =

= 5 g/dm

^{3}