To determine which of the given salts has an acidic aqueous solution, let's analyze each option:
a) NaCl (Sodium Chloride):
- Sodium chloride is formed from the neutralization of a strong acid (hydrochloric acid, HCl) and a strong base (sodium hydroxide, NaOH).
- When dissolved in water, it dissociates into Na⁺ and Cl⁻ ions, neither of which significantly hydrolyze in water.
- Consequently, the aqueous solution of NaCl is neutral (pH ~7).
b) CuSO4 (Copper(II) Sulfate):
- Copper(II) sulfate is formed from copper(II) hydroxide (Cu(OH)₂) and sulfuric acid (H₂SO₄).
- When CuSO₄ dissolves in water, it dissociates into Cu²⁺ and SO₄²⁻ ions. The Cu²⁺ ions hydrolyze in water to form copper(II) hydroxide (Cu(OH)₂) and release H⁺ ions.
- This results in the production of H⁺ ions, making the solution acidic (pH < 7).
c) Na2CO3 (Sodium Carbonate):
- Sodium carbonate is formed from the reaction of a weak acid (carbonic acid, H₂CO₃) and a strong base (sodium hydroxide, NaOH).
- When dissolved in water, sodium carbonate dissociates into Na⁺ and CO₃²⁻ ions. The CO₃²⁻ ions hydrolyze to form HCO₃⁻ and OH⁻ ions.
- This results in the production of OH⁻ ions, making the solution basic (pH > 7).
d) K2SO4 (Potassium Sulfate):
- Potassium sulfate is formed from the reaction of a strong acid (sulfuric acid, H₂SO₄) and a strong base (potassium hydroxide, KOH).
- When dissolved in water, it dissociates into K⁺ and SO₄²⁻ ions, neither of which significantly hydrolyze in water.
- Consequently, the aqueous solution of K2SO4 is neutral (pH ~7).
Based on the above analysis, the aqueous solution of CuSO₄ (Copper(II) Sulfate) is acidic.
So, the correct answer is:
b) CuSO4
