Why is copper sulphate an acidic salt?

Copper sulphate (CuSO₄) is considered an acidic salt because its aqueous solution produces an acidic medium (pH < 7) due to the behavior of its ions in water.

Reason behind its acidic nature:

Copper sulphate is formed from:

• Strong acid: Sulphuric acid (H₂SO₄)
• Weak base: Copper hydroxide (Cu(OH)₂)

Salts formed from a strong acid and weak base typically show acidic properties in solution.

What happens in water?

When CuSO₄ dissolves in water:

CuSO₄ → Cu²⁺ + SO₄²⁻

• The Cu²⁺ ions undergo hydrolysis:
  Cu²⁺ + H₂O ⇌ CuOH⁺ + H⁺
• This releases H⁺ ions, making the solution acidic.
• The SO₄²⁻ ions (from a strong acid) do not significantly affect the pH.

Key Concept:

The acidic nature is mainly due to Cu²⁺ ions, not the sulphate ions.

Key Takeaway:

Copper sulphate is an acidic salt because it is derived from a strong acid and weak base, and its Cu²⁺ ions release H⁺ ions through hydrolysis, lowering the pH of the solution.