Chemistry/Y4/Salt Preparation

Solubility Rules

1. All nitrate salts are soluble.
2. All chloride salts are soluble except for lead (II) chloride, silver chloride and mercury (I) chloride
3. All sulphate salts are soluble except calcium sulphate, barium sulphate and lead (II) sulphate.
4. All oxides and hydroxide are insoluble except for group I and ammonium salts. Solubility of group II oxides and hydroxides increases down the group. However, it is important to remember than oxides and hydroxides are NOT salts.

Methods of salt preparation

Precipitation	Mix two relevant aqueous solutions Filter to obtain residue salt Wash residue with distilled water Dry residue between sheets of filter paper
Titration	Titrate with suitable indicator till endpoint is reached Repeat titration without indicator Heat obtained solution to 1/3 volume (for saturation) Leave to solution to cool Filter to obtain residue salt DO NOT WASH (else it will dissolve) Dry residue between sheets of filter paper
Excess Base	Add excess base/carbonate into acid, stirring and heating until no more can dissolve Filter off excess base to obtain filtrate Heat filtrate to 1/3 volume (for saturation) Leave to solution to cool Filter to obtain residue salt Dry residue between sheets of filter paper

Caveats

Salts can be prepared by reacting acid with metals. However, it is not recommended for the following:

1. Insoluble salts. A thin layer of the insoluble salt will form on the metal, hence preventing further reactions between the metal and the acid. Reaction thus ends prematurely.

1. Salts of unreactive metals (Pb, Cu, Ag). Being unreactive, they will not react with the acid.

1. Group I salts. Group I metals react with both the acid and the water in the acid, thus giving you the relevant soluble. Group I hydroxide mixed with the relevant salt.

Summary of Salt Preparation