Concentrations of solutions
2 marks · EasyA student claims that halving the volume of a solution, while keeping the amount of solute the same, will double its concentration. Explain why the student is correct. Use calculations in your answer.
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Common mistakes: States correct without calculation; Confuses concentration/volume relation
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Marking points
M1 · 1 mark · Describes or calculates that concentration = amount ÷ volume.
E1 · 1 mark · Explains doubling effect with calculation (e.g., c1 = n/V, c2 = n/(V/2) = 2n/V = 2c1) or a clear worked example.
Worked solution
Concentration is calculated by dividing the amount of solute by the volume of the solution: c = n / V.
If the original concentration is c = n / V, then after halving the volume: c' = n / (V/2) = 2n / V = 2c.
This means the concentration doubles when the volume is halved and the amount of solute stays the same.