Preparation of Salts

Preparation of salts in the laboratory

The method used to prepare a salt depends on the solubility of the salt in water.
A soluble salt can be prepared from a reaction between an acid and a metal, a base or a carbonate.
- Reaction 1: Acid + alkali → salt + water
- Reaction 2: Acid + metal → salt + hydrogen
- Reaction 3: Acid + base → salt + water
- Reaction 4: Acid + metal carbonate → salt + water + carbon dioxide
Reaction 1 is used to prepare ammonium salts, sodium salts and potassium salts.
Reactions 2, 3 and 4 are used to prepare soluble salts except ammonium salts, sodium salts or potassium salts.
Recrystallisation is carried out to obtain pure crystals of the salt from the solution.

1. By the reaction between metal and acid : Certain metals (for example, Zn and Mg) react with HCl or H₂SO₄ to form salt and hydrogen.

Zn + 2HCl → ZnCl₂ + H₂

Zn + H₂SO₄ → ZnSO₄ + H₂

2. By the reaction between an acid and a base : All acid-base reactions (neutralization reactions) produce salts.

NaOH + HCl → NaCl + H₂O

CuO + 2HCl → CuCl₂ + H₂O

3. By direct union of a metal and a nonmetal : Sodium and chlorine combine directly to form sodium chloride.

2Na + Cl₂ → 2NaCl

Similarly, when sulphur is heated with iron filings, ferrous sulphide (FeS) is formed.

4. By the union between an acidic oxide and a basic :
Preparation of Salts 1
5. By the reaction between a metal and a base : When zinc is heated with an aqueous solution of NaOH, sodium zincate (salt) is formed with the evolution of hydrogen gas.