In which of the following case pH is greater than 7 ?

Options

A. 50 ml of 0.01 M HCI+50 ml of 0.1 M NaCI
B. 50 ml of 0.1 M `H_2SO_4` +50 ml of 0.2 M NaOH
C. 50 ml of 0.1 M `CH_3COOH` +50 mol of 0.1 M KOH
D. 50 ml of 0.1 M `HNO_3` +50 ml of 0.1 `NH_3`

Answer

To determine in which case the pH is greater than 7, we need to analyze each option provided. Let's go through them step by step.

### Step 1: Analyze the first option
**Option 1:** 50 ml of 0.01 molar HCl + 50 ml of 0.1 molar NaCl

- HCl is a strong acid, and when dissolved, it dissociates completely to produce H⁺ ions.
- NaCl is a neutral salt formed from a strong acid (HCl) and a strong base (NaOH).
- The pH of a strong acid solution is less than 7. Therefore, the pH of this combination will also be less than 7.

**Conclusion for Option 1:** pH < 7

**Hint:** Strong acids like HCl will always produce a pH less than 7 when in solution.

### Step 2: Analyze the second option
**Option 2:** 50 ml of 0.1 molar H₂SO₄ + 50 ml of 0.2 molar NaOH

- H₂SO₄ is a strong acid that dissociates to produce 2 moles of H⁺ for every mole of H₂SO₄. Thus, 0.1 M H₂SO₄ produces 0.2 M H⁺.
- NaOH is a strong base that dissociates completely to produce OH⁻ ions.
- Since both solutions have equal volumes (50 ml) and the concentration of H⁺ and OH⁻ ions are equal (0.2 M), they will completely neutralize each other.
- The resulting solution will have a pH of 7.

**Conclusion for Option 2:** pH = 7

**Hint:** A strong acid and a strong base in equal concentrations and volumes will result in a neutral solution (pH = 7).

### Step 3: Analyze the third option
**Option 3:** 50 ml of 0.1 molar CH₃COOH + 50 ml of 0.1 molar KOH

- CH₃COOH (acetic acid) is a weak acid, while KOH is a strong base.
- When mixed, the weak acid will react with the strong base to form a salt (CH₃COOK) and water.
- The resulting solution will be basic because the strong base (KOH) will dominate the pH, leading to a pH greater than 7.

**Conclusion for Option 3:** pH > 7

**Hint:** The combination of a weak acid and a strong base typically results in a solution with a pH greater than 7.

### Step 4: Analyze the fourth option
**Option 4:** 50 ml of 0.1 molar HNO₃ + 50 ml of 0.1 molar NH₃

- HNO₃ is a strong acid, while NH₃ is a weak base.
- When mixed, they will form NH₄NO₃, a salt.
- Since HNO₃ is a strong acid, it will dominate the pH, resulting in a solution with a pH less than 7.

**Conclusion for Option 4:** pH < 7

**Hint:** A strong acid combined with a weak base will generally yield a solution with a pH less than 7.

### Final Conclusion
The only case where the pH is greater than 7 is in **Option 3**: 50 ml of 0.1 molar CH₃COOH + 50 ml of 0.1 molar KOH.