Measuring solubility [chemistry only]
2 marks · EasyExplain why it is important to heat the evaporating basin until its mass remains constant when measuring the solubility of a salt.
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Common mistakes: Only stating that it is a 'fair test'; Not mentioning complete evaporation of water
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Marking points
M1 · 1 mark · Explains that repeated heating ensures all the water has evaporated.
A1 · 1 mark · States that this gives the correct mass of the salt left behind, so the measurement is accurate.
Worked solution
Heating to constant mass ensures all the water has evaporated. This means the remaining mass is only the salt, giving an accurate measurement of its mass and therefore correct calculation of solubility.