Measuring solubility [chemistry only]
4 marks · NormalThe graph below shows the solubility of two different salts (potassium nitrate and sodium chloride) in water as the temperature increases.
Using the graph, estimate the solubility of potassium nitrate in water at 30°C.
State which salt is more soluble at 0°C. Justify your answer using data from the graph.
Explain what is meant by a 'solubility curve'.
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.
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(a) About 48 g/100 g water
(b) Sodium chloride is more soluble at 0°C because its solubility (36 g/100 g water) is higher than that of potassium nitrate (13 g/100 g water). · must show Correct salt identified, Uses data from graph
(c) A solubility curve is a graph showing how the solubility of a substance in a solvent changes with temperature. · must show Graph/curve, Solubility vs Temperature
Also accept: Accept answers within ±2 units for estimation.; Allow 'shows how solubility changes with temperature' for c.
Common mistakes: Mixing up which line is which salt.; Omitting the temperature/solubility axes in definition.
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Marking points
A1 (a) · 1 mark · Correctly estimates the solubility of potassium nitrate at 30°C (allow ±2 g).
B1 (b) · 1 mark · Identifies sodium chloride as more soluble at 0°C with a correct justification from the graph.
B1 (c) · 1 mark · States a solubility curve shows solubility versus temperature (or similar).
B1 (c) · 1 mark · Mentions it is a graph or curve, or refers to plotting or appearance.
Worked solution
a) At 30°C, potassium nitrate's solubility is roughly halfway between 32 and 64 g/100 g water, so about 48 g/100 g water. b) Sodium chloride is more soluble at 0°C, as its solubility is 36 g/100 g water, while potassium nitrate's is 13 g/100 g water. c) A solubility curve is a graph that shows how the solubility of a substance in a particular solvent changes as the temperature changes.