Salt preparations
2 marks · EasyA solution containing 10 g of sodium chloride is left to crystallise. If the maximum solubility of sodium chloride in water at room temperature is 36 g per 100 g of water, calculate whether all the salt will dissolve in 20 g of water.
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No, because only 7.2 g can dissolve g (±0.1)
Also accept: No, not all will dissolve; Only 7.2 g will dissolve
Common mistakes: 10; 36
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Marking points
M1 · 1 mark · Correctly calculates how much sodium chloride can dissolve in 20 g of water: (36/100) × 20 = 7.2 g.
A1 · 1 mark · Concludes that not all 10 g will dissolve (as only 7.2 g will dissolve).
Worked solution
Solubility = 36 g per 100 g water. For 20 g water, maximum salt that can dissolve = (36/100) × 20 = 7.2 g.
Therefore, not all of the 10 g will dissolve; only 7.2 g will dissolve.