Question

Complete and balance the following chemical equations: \( 3 \text{MnO}_4^- + 4 \text{H}^+ \longrightarrow ? \)
\( \text{Cr}_2 \text{O}_7^{2-} + 14 \text{H}^+ + 6 \text{Fe}^{2+} \longrightarrow ? \)

Hint:

In redox reactions, balancing involves ensuring that both mass and charge are conserved. For example, in the reduction of permanganate to manganese dioxide, balance oxygen atoms with water and hydrogen ions to balance charge.

Answer 1

The first equation represents the reduction of permanganate ions (\( \text{MnO}_4^- \)) in acidic medium. The balanced equation is:
\[ 3 \text{MnO}_4^- + 4 \text{H}^+ \longrightarrow 2 \text{MnO}_4^- + \text{MnO}_2 + 2 \text{H}_2\text{O} \] Explanation:
- Permanganate (\( \text{MnO}_4^- \)) is reduced to manganese dioxide (\( \text{MnO}_2 \)) in acidic medium.
- The oxidation state of manganese in \( \text{MnO}_4^- \) is +7, and it is reduced to +4 in \( \text{MnO}_2 \), releasing oxygen and water. (b) The second equation represents the reaction of dichromate ions (\( \text{Cr}_2 \text{O}_7^{2-} \)) in acidic medium, where it is reduced by \( \text{Fe}^{2+} \) to form \( \text{Cr}^{3+} \) ions. The balanced equation is:
\[ \text{Cr}_2 \text{O}_7^{2-} + 14 \text{H}^+ + 6 \text{Fe}^{2+} \longrightarrow 2 \text{Cr}^{3+} + 6 \text{Fe}^{3+} + 7 \text{H}_2\text{O} \] Explanation:
- Dichromate (\( \text{Cr}_2 \text{O}_7^{2-} \)) is reduced to \( \text{Cr}^{3+} \) in the presence of acidic conditions.
- The iron (\( \text{Fe}^{2+} \)) acts as a reducing agent and is oxidized to \( \text{Fe}^{3+} \).
- The reduction of dichromate involves the transfer of electrons and the formation of water as a product.