Correct Option
Copper sulphate (CuSO₄) is a salt formed from the reaction of a strong acid (sulphuric acid, H₂SO₄) and a weak base (copper hydroxide, Cu(OH)₂). When such a salt dissolves in water, the cation derived from the weak base undergoes hydrolysis. In this process, the Cu²⁺ ions react with water molecules, leading to the formation of hydronium ions (H₃O⁺) or hydrogen ions (H⁺).
The reaction can be represented as:
Cu²⁺ + H₂O ⇌ CuOH⁺ + H⁺
The release of H⁺ ions into the solution increases its acidity, thereby lowering the pH and making the aqueous copper sulphate solution acidic in nature.
Incorrect Options
- Dialysis: This is a separation process that involves the differential diffusion of solutes through a semi-permeable membrane. It is used to separate colloids from crystalloids or to purify blood, and it does not explain the acidic nature of a salt solution.
- Electrolysis: This is a process that uses an electric current to drive a non-spontaneous chemical reaction, typically to decompose compounds. It is not the spontaneous chemical interaction responsible for the acidity of copper sulphate in water.
- Photolysis: This refers to the chemical decomposition of a compound by light energy (photons). This phenomenon is not relevant to the acidic behaviour of copper sulphate when dissolved in water.