Solubility rules and making insoluble salts

Some salts dissolve in water and some do not. Knowing which helps you predict precipitates and choose how to make a salt.

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The solubility rules

CompoundsSoluble?
All common sodium, potassium and ammonium saltsSoluble
All nitratesSoluble
Most chloridesSoluble, except silver chloride and lead chloride
Most sulfatesSoluble, except lead sulfate, barium sulfate and calcium sulfate
Most carbonates and hydroxidesInsoluble, except sodium, potassium and ammonium ones

Predicting precipitates

When two solutions are mixed, the ions swap partners. If one new combination is insoluble, it forms a solid precipitate.
silver nitrate + sodium chloride → silver chloride (white precipitate) + sodium nitrate
Ionic equation: Ag+(aq) + Cl−(aq) → AgCl(s)
barium chloride + sodium sulfate → barium sulfate (white precipitate) + sodium chloride

Making a pure, dry insoluble salt

1. Mix solutions of two soluble salts that contain the ions you need.
2. Filter to collect the precipitate.
3. Wash it on the filter paper with distilled water to remove the soluble salt left with it.
4. Dry it in a warm oven or between filter papers.
Worked example

Lead(II) nitrate solution is mixed with potassium iodide solution. Predict the precipitate.

  1. The ions swap: lead iodide and potassium nitrate could form.
  2. Potassium salts and nitrates are all soluble.
  3. So lead iodide must be the precipitate (it is yellow).

Answer: Lead(II) iodide

Key idea

Sodium, potassium, ammonium salts and nitrates are soluble. Silver and lead chlorides are insoluble; lead, barium and calcium sulfates are insoluble; most carbonates and hydroxides are insoluble. Mix two solutions, filter, wash with distilled water and dry to make an insoluble salt.

Key words
Solubility
The mass of solute that dissolves in 100 g of solvent at a given temperature, in g per 100 g of solvent.
Salt
The compound formed when the hydrogen of an acid is replaced by a metal or ammonium ion.
Precipitate
An insoluble solid that forms when two solutions react.

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Extra practice

2 more questions

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  1. Which of these salts would NOT dissolve in water?

    1. Sodium sulfate
    2. Barium sulfate
    3. Ammonium chloride
    4. Potassium carbonate
    Show the answer

    Answer: Barium sulfate

    Barium, lead and calcium sulfates are insoluble.

  2. Which of these hydroxides is soluble in water?

    1. Iron(II) hydroxide
    2. Copper(II) hydroxide
    3. Magnesium hydroxide
    4. Potassium hydroxide
    Show the answer

    Answer: Potassium hydroxide

    Sodium, potassium and ammonium hydroxides are soluble.

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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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