Separation of mixtures
2 marks · EasyA sample of rock salt contains 16 g of sodium chloride mixed with 4 g of insoluble impurities. A student dissolves the sample in water, filters the solution, and then uses crystallisation to obtain sodium chloride crystals. What is the maximum mass of sodium chloride crystals the student can expect to obtain after crystallisation? Assume no losses occur during the process.
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16 g (±0)
Common mistakes: Adding the masses; Subtracting impurity from total without understanding
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Marking points
M1 · 1 mark · Identifies that only the sodium chloride mass is collected (not impurities)
A1 · 1 mark · Correct final answer: 16 g (with or without unit; must not add impurities)
Worked solution
Only the sodium chloride can be obtained as crystals after dissolving and filtering, because the impurities are insoluble and left behind on the filter paper.
Mass of sodium chloride crystals obtained = 16 g.