Measuring solubility [chemistry only]
3 marks · EasyThe diagram below shows a solubility curve for a salt.
State the solubility of salt W at 20°C.
Describe what happens to the solubility of salt W as the temperature increases from 0°C to 60°C.
Explain, with reference to the solubility curve, how to tell when a solution of salt W at 40°C is saturated.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a.i) 32 g/100g water
(a.ii) The solubility of salt W increases as temperature increases.
(a.iii) A solution at 40°C is saturated when it contains 50g of salt W per 100g of water and any extra salt will not dissolve.
Show mark scheme and worked solution
Marking points
A1 (a(i)) · 1 mark · Correctly reads solubility from the graph at 20°C (accept 31–33 g/100g water)
B1 (a(ii)) · 1 mark · States that the solubility increases with temperature
B2 (a(iii)) · 1 mark · Explains that a solution is saturated when it contains the maximum mass (50g per 100g water at 40°C) and extra salt will not dissolve
Worked solution
a.i To find the solubility of salt W at 20°C, read from the graph:
a.ii As temperature increases from 0°C to 60°C, the solubility of salt W increases.
a.iii At 40°C, the saturated solution contains 50g salt W per 100g water (from the graph). If any more salt is added, it will not dissolve and will remain as solid.