Question

Which among the following salt solutions in water shows pH less than 7?

• A. CuCl2
• B. CH3COONH4
• C. Na2CO3
• D. KNO3

Answer 1

Answer: (A)

CuCl₂

Answer 2

1. CuCl₂:

   • Cu²⁺ is a metal cation that undergoes hydrolysis to produce H⁺ ions, making the solution acidic.
   • Cl⁻ comes from a strong acid (HCl) and does not affect the pH significantly.
   • Thus, a solution of CuCl₂ is acidic (pH < 7).

2. CH₃COONH₄:

   • Derived from a weak acid (CH₃COOH) and a weak base (NH₄OH), its hydrolysis effects nearly cancel out.
   • It is approximately neutral.

3. Na₂CO₃:

   • Na⁺ is neutral (from strong base NaOH) and CO₃²⁻ is the conjugate base of a weak acid (H₂CO₃).
   • The solution produces OH⁻ on hydrolysis, making it basic (pH > 7).

4. KNO₃:

   • K⁺ is neutral (from strong base KOH) and NO₃⁻ is neutral (from strong acid HNO₃).
   • The overall solution is neutral.