Making insoluble salts [GCSE Chemistry only]
To make an insolubleUnable to dissolve in a particular solvent. For example, sand is insoluble in water. salt, two solubleAble to dissolve in solvent. For example, sugar is soluble in water because it dissolves to form sugar solution. salts need to react together in a precipitation reactionA reaction in which an insoluble solid is formed when certain solutions are mixed..
The table shows soluble and insoluble salts:
| Soluble | Insoluble |
| All nitrates | None |
| All common sodium, potassium and ammonium salts | None |
| Most common sulfates | Calcium sulfate and barium sulfate |
| Most common chlorides | Silver chloride |
| Lithium, sodium, potassium and ammonium carbonates | Most common carbonates |
| Soluble | All nitrates |
|---|---|
| Insoluble | None |
| Soluble | All common sodium, potassium and ammonium salts |
|---|---|
| Insoluble | None |
| Soluble | Most common sulfates |
|---|---|
| Insoluble | Calcium sulfate and barium sulfate |
| Soluble | Most common chlorides |
|---|---|
| Insoluble | Silver chloride |
| Soluble | Lithium, sodium, potassium and ammonium carbonates |
|---|---|
| Insoluble | Most 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 鈫 sodium nitrate + silver chloride
AgNO3(aq) + NaCl(aq) 鈫 NaNO3(aq) + AgCl(s)
The ionic equation for this process is as follows:
Ag+(aq) + Cl鈥(aq) 鈫 AgCl(s)
The silver chloride appears as tiny particles suspensionA mixture of two substances, one of which is finely divided throughout the other. in the reaction mixture 鈥 this is the precipitateA suspension of particles in a liquid formed when a dissolved substance reacts to form an insoluble substance, eg in a precipitation reaction.. 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) 鈫 BaSO4(s) + MgCl2(aq)
The ionic equation for this process is as follows:
Ba2+(aq) + SO42鈥(aq) 鈫 BaSO4(s)