The pH of 0.1 M solution of the following salts increases in the order

Options

A. `KCl lt NH_4Cl lt NaCN lt HCl`
B. `HCl lt NH_4Cl lt KCl lt NaCN`
C. `NaCN lt NH_4Cl lt KCl lt HCl`
D. `HCl lt KCl lt NaCN lt NH_4 Cl`

Answer

To determine the order of increasing pH for a 0.1 M solution of the given salts (KCl, NH4Cl, NaCl, and HCl), we need to analyze the hydrolysis of each salt and their resultant pH in solution.

### Step-by-Step Solution:

1. **Identify the nature of each salt:**
- KCl: Composed of K+ (from a strong base KOH) and Cl- (from a strong acid HCl).
- NH4Cl: Composed of NH4+ (from a weak base NH3) and Cl- (from a strong acid HCl).
- NaCl: Composed of Na+ (from a strong base NaOH) and Cl- (from a strong acid HCl).
- HCl: A strong acid that dissociates completely in solution.

2. **Analyze KCl:**
- K+ does not hydrolyze as it is the cation of a strong base (KOH).
- Cl- does not hydrolyze as it is the anion of a strong acid (HCl).
- Therefore, KCl is neutral and will have a pH of around 7.

3. **Analyze NH4Cl:**
- NH4+ can hydrolyze in water:
\[ NH4^+ + H2O \rightleftharpoons NH3 + H3O^+ \]
- This reaction produces H3O+, making the solution acidic.
- Thus, the pH of NH4Cl will be less than 7.

4. **Analyze NaCl:**
- Similar to KCl, Na+ does not hydrolyze (as it is from NaOH, a strong base).
- Cl- does not hydrolyze (as it is from HCl, a strong acid).
- Therefore, NaCl is also neutral and will have a pH of around 7.

5. **Analyze HCl:**
- HCl is a strong acid that dissociates completely in solution:
\[ HCl \rightarrow H^+ + Cl^- \]
- This results in a high concentration of H3O+, leading to a very low pH (around 1-2).

6. **Determine the order of increasing pH:**
- HCl has the lowest pH (most acidic).
- NH4Cl has a pH less than 7 (acidic).
- KCl and NaCl are neutral with a pH around 7, but since they are both neutral, we can consider them equal in pH.

### Final Order of Increasing pH:
- HCl < NH4Cl < KCl = NaCl