Question

Write the balance equation showing the oxidation of Fe2+ ions to Fe3+ ions by dichromate ions ( Cr2O72-) in an acidic medium

Answer 1

To balance the equation for the oxidation of Fe²⁺ ions to Fe³⁺ ions by dichromate ions (Cr₂O₇²⁻) in an acidic medium, we need to follow these steps:

1. **Identify the Half-Reactions**:
- The oxidation half-reaction: \( \text{Fe}^{2+} \rightarrow \text{Fe}^{3+} \)
- The reduction half-reaction (for dichromate): \( \text{Cr}_2\text{O}_7^{2-} \rightarrow \text{Cr}^{3+} \)

2. **Balance the Half-Reactions**:
- **Oxidation of Fe**:
\[
\text{Fe}^{2+} \rightarrow \text{Fe}^{3+} + e^{-}
\]
- **Reduction of Dichromate** in acidic medium:
To balance Cr and O, we add water and hydrogen ions as needed:
\[
\text{Cr}_2\text{O}_7^{2-} + 14\text{H}^+ + 6e^{-} \rightarrow 2\text{Cr}^{3+} + 7\text{H}_2\text{O}
\]

3. **Balance the Electrons**:
To combine the half-reactions, we need to balance the number of electrons transferred. Because the oxidation of one Fe²⁺ gives one electron, and the reduction of dichromate uses 6 electrons, we will multiply the oxidation half-reaction by 6:
\[
6\text{Fe}^{2+} \rightarrow 6\text{Fe}^{3+} + 6e^{-}
\]

4. **Combine the Half-Reactions**:
Now we can combine the two balanced half-reactions:
\[
6\text{Fe}^{2+} + \text{Cr}_2\text{O}_7^{2-} + 14\text{H}^+ \rightarrow 6\text{Fe}^{3+} + 2\text{Cr}^{3+} + 7\text{H}_2\text{O}
\]

5. **Final Balanced Equation**:
The final balanced redox reaction in acidic medium is:
\[
6\text{Fe}^{2+} + \text{Cr}_2\text{O}_7^{2-} + 14\text{H}^+ \rightarrow 6\text{Fe}^{3+} + 2\text{Cr}^{3+} + 7\text{H}_2\text{O}
\]

This equation represents the oxidation of ferrous ions to ferric ions by dichromate ions in an acidic medium.