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The solubility of solids increases as temperature increases, while the solubility of gases decreases as temperature increases.

You can determine the solubility of a solid in water:

1. Weigh a known mass of a solid.
2. Measure 10cm³ of water. (The density of water is 1 g/cm³, so 10cm³ = 10 g)
3. Add the solid to the water and heat until the solid dissolves.
4. Cool the mixture and record the temperature, in °C, at which crystals begin to form. The mass of solid added is the mass of this substance required to saturate 10 g of water at the temperature recorded. Multiplying the mass of the substance by 10 gives the solubility in g/100 g water.
5. Repeat with different masses of solid.
6. Plot a graph of the mass of solid in grams per 100 g of water, against the temperature in °C.

(Higher tier only)

A solid’s solubility decreases with decreasing temperature. When a hot, concentrated solution is cooled, some of the solute will be deposited.

Example

Calculate the mass of solid that is deposited if a solution containing 15 g per 100 g of water at 30°C is cooled to 10°C.

Solubility of the solid at 30°C is 15 g / 100 g water, and 10 g / 100 g water at 10°C.

Mass of solid deposited = 15 – 10 = 5 g per 100 g of water

Simple scaling may be required.