When potassium permanganate is titrated against ferrous ammonium sulphate, the equivalent weight of potassium permanganent is

Options

A. (a)`("molecular mass")/(3)`
B. (b)`("molecular mass")/(5)`
C. (c)`("molecular mass")/(2)`
D. (d)`("molecular mass")/(10)`

Answer

To find the equivalent weight of potassium permanganate (KMnO4) when titrated against ferrous ammonium sulfate (Mohr's salt), we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Compounds:**
- Potassium permanganate (KMnO4) is the oxidizing agent.
- Ferrous ammonium sulfate (FeSO4·(NH4)2SO4·6H2O) contains Fe²⁺ ions that will be oxidized.

2. **Write the Reaction:**
- The oxidation reaction involves the conversion of Fe²⁺ to Fe³⁺.
- The reduction reaction involves the conversion of MnO4⁻ (where Mn is in the +7 oxidation state) to Mn²⁺ (where Mn is in the +2 oxidation state).

3. **Determine the Oxidation States:**
- In KMnO4, the oxidation state of Mn is +7.
- In the reaction, MnO4⁻ is reduced to Mn²⁺, which means it gains 5 electrons (from +7 to +2).

4. **Balance the Reaction:**
- The balanced half-reaction for the reduction of MnO4⁻ is:
\[ \text{MnO}_4^- + 8 \text{H}^+ + 5 \text{e}^- \rightarrow \text{Mn}^{2+} + 4 \text{H}_2\text{O} \]
- The oxidation half-reaction for Fe²⁺ is:
\[ \text{Fe}^{2+} \rightarrow \text{Fe}^{3+} + \text{e}^- \]

5. **Determine the n-factor:**
- The n-factor for KMnO4 in this reaction is the number of electrons transferred, which is 5.

6. **Calculate the Molecular Weight of KMnO4:**
- The molecular weight of KMnO4 can be calculated as follows:
- K (Potassium) = 39 g/mol
- Mn (Manganese) = 55 g/mol
- O (Oxygen) = 16 g/mol × 4 = 64 g/mol
- Total = 39 + 55 + 64 = 158 g/mol

7. **Calculate the Equivalent Weight:**
- The formula for equivalent weight is:
\[ \text{Equivalent Weight} = \frac{\text{Molecular Weight}}{\text{n-factor}} \]
- Substituting the values:
\[ \text{Equivalent Weight of KMnO}_4 = \frac{158 \text{ g/mol}}{5} = 31.6 \text{ g/equiv} \]

### Final Answer:
The equivalent weight of potassium permanganate (KMnO4) is **31.6 g/equiv**.

---