Solutions and solubility

Some substances dissolve easily, some barely dissolve, and there is always a limit to how much will dissolve.

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Key words

Solute: the substance that dissolves (sugar). Solvent: the liquid it dissolves in (water). Solution: the mixture made.
Soluble: can dissolve. Insoluble: cannot dissolve (sand in water).
Water is not the only solvent. Nail varnish is insoluble in water but dissolves in propanone (nail varnish remover).

Saturated solutions

If you keep adding solute, a point comes when no more will dissolve. The solution is saturated.
Solubility is the mass of solute that dissolves in 100 g of water at a given temperature, to make a saturated solution.
For most solids, solubility increases as the temperature rises.

Using solubility data

If solubility is 40 g per 100 g of water, then 50 g of water dissolves half as much: 20 g.
If a hot saturated solution cools, the solubility falls, so some solid comes back out as crystals.
Mass of crystals = mass dissolved when hot minus mass that can stay dissolved when cool.
Data for an imaginary solid X.
Temperature (°C)Solubility of solid X (g per 100 g water)
2035
4060
6085
Worked example

Using the table for solid X: 100 g of water is saturated with X at 40 °C, then cooled to 20 °C. What mass of crystals forms?

  1. At 40 °C, 60 g is dissolved.
  2. At 20 °C, only 35 g can stay dissolved.
  3. 60 − 35

Answer: 25 g of crystals

Key idea

Solute + solvent = solution. A saturated solution can dissolve no more solute. Solubility is grams per 100 g of water and usually rises with temperature. Cooling a hot saturated solution makes crystals.

Key words
Solute
The substance that dissolves in a solvent.
Solvent
The liquid that a solute dissolves in.
Water
Pure water melts at 0 °C and boils at 100 °C. Its density is 1 g/cm³. Ice is less dense than water, so it floats.
Mixture
Two or more substances mixed but not chemically joined, so they can be separated.
Mass
The amount of matter in an object, measured in kilograms (kg). It is the same everywhere.

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2 more questions

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  1. Sugar dissolves in tea. What is the tea?

    1. A gas
    2. The solute
    3. Insoluble
    4. The solvent
    Show the answer

    Answer: The solvent

    The solvent does the dissolving.

  2. How can you tell a solution is saturated?

    1. The solution is hot
    2. Extra solute stays undissolved however much you stir
    3. The solution has no solute
    4. The solution is clear
    Show the answer

    Answer: Extra solute stays undissolved however much you stir

    No more can dissolve at that temperature.

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Sources and references

Checked by the GCSE-ready editorial team, 17 October 2026. Last updated 2 October 2026. Spotted a mistake? Tell us and we will fix it.

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