GCSE Combined Science revision · Chemistry: atoms, bonding and amounts

Concentration of solutions

The idea

Concentration is the mass of solute in a given volume of solution: concentration (g/dm³) = mass of solute (g) ÷ volume (dm³). 1 dm³ = 1000 cm³. A more concentrated solution has more solute in the same volume.

Convert cm³ to dm³ by dividing by 1000.
Use concentration = mass ÷ volume.
Rearrange to find mass or volume.

Watch out Forgetting to convert cm³ into dm³ gives an answer 1000 times too small.

See it worked

Worked example

5.0 g of sodium chloride is dissolved to make 250 cm³ of solution. Calculate the concentration in g/dm³.

250 cm³ = 0.250 dm³.
Concentration = 5.0 ÷ 0.250 = 20 g/dm³.

Answer 20 g/dm³

Your turn

Question 1Calculator allowed2 marks

What mass of solute is in 500 cm³ of a 40 g/dm³ solution?

Question 2Calculator allowed2 marks

12 g of copper sulfate is dissolved to make 200 cm³ of solution. What is the concentration in g/dm³?

Question 3Calculator allowed1 mark

How many cm³ are in 1 dm³?

In past papers

25 official questions in 25 papers since 2018. The latest:

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