The effect of temperature on solubility

In general, solids become more soluble as the temperature increases. This is why sugar dissolves better in hot water than in cold water. The table shows three examples of the solubility (g of solute per 100 g water) of substances at different temperatures.

20°C30°C40°C
Lead(II) nitrate54.363.472.1
Potassium nitrate31.645.863.9
Sodium chloride35.936.136.4

Solubility curves

Every solute has a fixed solubility at room temperature. However, the solubility of a solute changes as the temperature of the water changes. The solubility of a substance in water at different temperatures can be displayed using a solubility curve. Solubility curves can be used to determine the mass of crystals formed when a solution is cooled.

Graph showing the solubility curves of potassium nitrate, lead(II) nitrate, and sodium chloride.

Each solute has a different solubility at different temperatures and the change in solubility with temperature depends on the solute.

The curves show that:

  • solubility of all three solutes increases as temperature increases
  • the solubility of potassium nitrate increases the most from approximately 30 g per 100 g water to over 200 g per 100 g water
  • the solubility of sodium chloride hardly changes at all
  • sodium chloride and lead(II) nitrate are more soluble than potassium nitrate at low temperatures
  • the solubility of lead(II) nitrate and potassium nitrate is the same at about 50°C (approximately 80 g per 100 g water, where the solubility curves of these substances cross)
  • the solubility of sodium chloride and potassium nitrate is the same at about 23°C (approximately 38 g per 100 g water, where the solubility curves of these substances cross)
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