Solubility Rules - GCSE Chemistry (Single Science) Revision - BBC

In this guide

1. Revise
2. Video
3. Audio
4. Test

Pages

1. Making salts from acids and insoluble reactants
2. How to make copper sulfate crystals
3. Making salts from acids and alkalis
4. Solubility rules
5. Making insoluble salts

Solubility rules

Solubility

A substance's solubility is a measure of the maximum mass that will dissolve in a given volume of solvent, at a particular temperature. Substances that are very soluble have high solubilities. Substances that are insoluble or sparingly soluble (almost none dissolves) have low solubilities.

Solubility in water

The table summarises whether common ionic compounds are soluble or insoluble in water.

Soluble	Insoluble
All common sodium, potassium and ammonium salts
All nitrates
Most common chlorides	Silver chloride, lead chloride
Most common sulfates	Lead sulfate, barium sulfate, calcium sulfate
Sodium carbonate, potassium carbonate, ammonium carbonate	Most common carbonates
Sodium hydroxide, potassium hydroxide, ammonium hydroxide	Most common hydroxides

Soluble	All common sodium, potassium and ammonium salts
Insoluble

Soluble	All nitrates
Insoluble

Soluble	Most common chlorides
Insoluble	Silver chloride, lead chloride

Soluble	Most common sulfates
Insoluble	Lead sulfate, barium sulfate, calcium sulfate

Soluble	Sodium carbonate, potassium carbonate, ammonium carbonate
Insoluble	Most common carbonates

Soluble	Sodium hydroxide, potassium hydroxide, ammonium hydroxide
Insoluble	Most common hydroxides

The top two rows explain why so many salt solutions used in the laboratory are sodium or potassium compounds or nitrates.

Precipitates

A precipitate is an insoluble product that forms when two solutions are mixed and react together. The reaction that produces a precipitate is called a precipitation reaction.

For example, a precipitate of lead iodide forms when potassium iodide solution and lead nitrate solution are mixed:

potassium iodide + lead nitrate → potassium nitrate + lead iodide

2KI(aq) + Pb(NO3)2(aq) → 2KNO3(aq) + PbI2(s)

Notice how important state symbols are in the balanced equations for precipitation reactions. Without the (s) for solid, it would not be obvious that PbI2 (lead iodide) was the precipitate.

Predicting precipitates

The formation of a precipitate, when two solutions are mixed, can be predicted using the solubility rules in the table:

• if the products meet the 'soluble' rules in the left hand column, no precipitate will form
• if at least one product meets the 'insoluble' rule in the right hand column, a precipitate will form

Worked example

Silver nitrate solution is mixed with sodium chloride solution. Predict whether a precipitate forms and name any precipitate.

Worked example answer

A precipitate of silver chloride will form.

Question

Potassium sulfate solution is mixed with barium chloride solution. Predict whether a precipitate forms, and name any precipitate.

Show answer

A precipitate of barium sulfate will form.

Next pageMaking insoluble saltsPrevious pageMaking salts from acids and alkalis

More guides on this topic

• Acids and alkalis - Edexcel
• Electrolysis - Edexcel
• Sample exam questions - chemical changes - Edexcel

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