Making insoluble salts [GCSE Chemistry only]

To make an insoluble salt, two soluble salts need to react together in a precipitation reaction.

The table shows soluble and insoluble salts:

All nitratesNone
All common sodium, potassium and ammonium saltsNone
Most common sulfatesCalcium sulfate and barium sulfate
Most common chloridesSilver chloride
Lithium, sodium, potassium and ammonium carbonatesMost common carbonates

We can see from the table that silver chloride is an insoluble salt. It can be made by reacting a soluble silver salt with a soluble chloride salt.

Silver nitrate and sodium chloride are both soluble. When their solutions are mixed together, soluble sodium nitrate and insoluble silver chloride are made:

silver nitrate + sodium chloride → sodium nitrate + silver chloride

AgNO3(aq) + NaCl(aq) → NaNO3(aq) + AgCl(s)

The ionic equation for this process is as follows:

Ag+(aq) + Cl(aq) → AgCl(s)

The silver chloride appears as tiny particles suspended in the reaction mixture – this is the precipitate. The precipitate can be filtered, washed with water on the filter paper, and then dried in an oven.

A similar reaction can be used to test for the presence of sulfate ions. Mixing a solution of barium chloride (or barium nitrate) with a solution containing sulfate forms a white precipitate.

MgSO4(aq) + BaCl2(aq) → BaSO4(s) + MgCl2(aq)

The ionic equation for this process is as follows:

Ba2+(aq) + SO42–(aq) → BaSO4(s)

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