In which of the following titrations phenolphthalein can be used as indicator ?

Options

A. NaOH with `H_(2)CO_(3)`
B. KOH with `CH_(3) COOH`
C. `NH_(4)OH` with HCl
D. `NH_(4) OH` with `CH_(3) COOH`

Answer

To determine in which of the following titrations phenolphthalein can be used as an indicator, we need to analyze each option based on the nature of the acids and bases involved. Phenolphthalein is an acid-base indicator that is colorless in acidic solutions and turns pink in basic solutions, with a pH range of 8 to 10.

### Step-by-Step Solution:

1. **Understand the nature of phenolphthalein**:
- Phenolphthalein is colorless in acidic solutions (pH < 8) and pink in basic solutions (pH > 10). It is typically used in titrations where the endpoint is in the basic range.

2. **Analyze the first titration: NaOH with H2CO3**:
- NaOH is a strong base and H2CO3 (carbonic acid) is a weak acid.
- In this titration, the reaction will produce a salt and water, and the resulting solution will be basic. Therefore, phenolphthalein can be used as an indicator.

3. **Analyze the second titration: KOH with CH3COOH**:
- KOH is a strong base and CH3COOH (acetic acid) is a weak acid.
- Similar to the first case, the resulting solution will be basic, allowing phenolphthalein to be used as an indicator.

4. **Analyze the third titration: NH4OH with HCl**:
- NH4OH (ammonium hydroxide) is a weak base and HCl is a strong acid.
- The resulting solution will be acidic, which means phenolphthalein cannot be used as an indicator.

5. **Analyze the fourth titration: NH4OH with CH3COOH**:
- Both NH4OH (weak base) and CH3COOH (weak acid) are involved.
- The resulting solution will be neutral or weakly acidic, so phenolphthalein cannot be used as an indicator.

### Conclusion:
Phenolphthalein can be used as an indicator in the following titrations:
- NaOH with H2CO3
- KOH with CH3COOH

### Final Answer:
The correct options are:
1. NaOH with H2CO3
2. KOH with CH3COOH

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