10 g of salt in 0.5 dm³ of solution gives 20 g/dm³. What is the concentration if the same mass is in 0.25 dm³?
- The mass is the same and the volume is halved.
- Concentration = 10 ÷ 0.25 = 40 g/dm³: it doubles.
Answer 40 g/dm³
GCSE Combined Science revision · Chemistry: atoms, bonding and amounts
The idea
Concentration depends on both the amount of solute and the volume of solution. Increasing the mass of solute in the same volume increases the concentration; increasing the volume of solvent for the same mass of solute decreases it (dilution).
- Say which changes: the solute or the volume.
- Predict the change in concentration.
- Use concentration = mass ÷ volume to check.
Watch out Adding water does not change the amount of solute, only the concentration.
See it worked
Your turn
100 cm³ of a 30 g/dm³ solution is diluted to 300 cm³. What is the new concentration in g/dm³?
What happens to the concentration if more solute is dissolved in the same volume?
A solution contains 8 g of solute in 0.4 dm³. Another 8 g of solute is dissolved in it without changing the volume. What is the new concentration in g/dm³?
In past papers
1 official question in 1 paper since 2018. The latest:
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