Question

Write two examples of each of the following:

(iii) Double salts

Answer 1

Double salt:

1. A double salt is a salt that contains more than one cation or more than one anion and is obtained by a combination of two different salts which were crystallized in the same regular ionic lattice.
2. Double salts should not be confused with complexes. Double salts only exist in the solid. When dissolved in water, a double salt acts as a mixture of the two separate salts.

Examples of double salts:

1. Potash alum:

1. Potash alum is a chemical compound widely used as the potassium sulfate dodecahydrate. It is double salt that is used commonly in medicine and the water treatment process.
2. The chemical formula of potash alum is ${\mathrm{K}}_2{\mathrm{SO}}_4.{\mathrm{Al}}_2{\left({\mathrm{SO}}_4\right)}_3.24{\mathrm{H}}_2\mathrm{O}$.
3. The crystalline solid that is formed is acidic and colourless.
4. The reaction is $\underset{\mathrm{Aluminium}\mathrm{sulphate}}{{\mathrm{Al}}_2{\left({\mathrm{SO}}_4\right)}_3\left(\mathrm{aq}\right)}+\underset{\mathrm{Potassium}\mathrm{sulphate}}{{\mathrm{K}}_2{\mathrm{SO}}_4\left(\mathrm{aq}\right)}\to \underset{\mathrm{Potash}\mathrm{alum}}{{\mathrm{K}}_2{\mathrm{SO}}_4.{\mathrm{Al}}_2{\left({\mathrm{SO}}_4\right)}_3.24{\mathrm{H}}_2\mathrm{O}\left(\mathrm{s}\right)}$

2. Dolomite: Dolomite ( CaCO₃.MgCO₃) is a double salt consisting of calcium carbonate (CaCO₃) and magnesium carbonate (MgO) and is one of the two forms of limestone. This dolomite can be found in the Bangkalan area, which is only used as a landfill and makes light stone.