GCSE Chemistry · AQA 8462 · Topic 4.3.4

Using concentrations of solutions in mol/dm³

Key points

Concentration is the amount of solute in a given volume of solution. Common units are g/dm³ and (Higher) mol/dm³.
$\text{concentration (g/dm}^3) = \frac{\text{mass of solute (g)}}{\text{volume (dm}^3)}$ . Remember 1 dm³ = 1000 cm³.
(Higher) $\text{concentration (mol/dm}^3) = \frac{\text{moles of solute}}{\text{volume (dm}^3)}$ . To convert mol/dm³ to g/dm³ multiply by $M_r$ .
A titration measures exactly what volume of one solution reacts with a known volume of another, using a burette, a pipette and an indicator to show the end point.
Repeat the titration until results are concordant (within 0.10 cm³) and use the mean of those.
(Higher) From the titre, calculate moles of the known solution, use the equation's mole ratio, then divide by the volume to find the unknown concentration.

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Concentrations in mol/dm³ let you work out how many moles are in a measured volume of solution. That is the key to titration calculations. This sub-topic is (Higher tier).

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