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Redox Reactions question

2024 · 31 Jan · Shift 2 · Q27
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Redox Reactions question

2024 · 31 Jan · Shift 2 · Q27

JEE MainChemistryRedox ReactionsNumerical+4 / −1
Number of moles of H+\mathrm{H}^{+}H+ ions required by 1 mole1 \mathrm{~mole}1 mole of MnO4−\mathrm{MnO}_4^{-}MnO4−​ to oxidise oxalate ion to CO2\mathrm{CO}_2CO2​ is ‾\underline{\hspace{2cm}}​.
Numerical answer
View written solutionFree

Correct answer: 8

  1. Write the relevant half-reaction for permanganate in acidic medium

In acidic medium, permanganate is reduced as:

MnO4−+8H++5e−→Mn2++4H2O\mathrm{MnO_4^- + 8H^+ + 5e^- \rightarrow Mn^{2+} + 4H_2O}MnO4−​+8H++5e−→Mn2++4H2​O

This shows that 1 mole of MnO4−\mathrm{MnO_4^-}MnO4−​ requires 8 moles of H+\mathrm{H^+}H+ for its reduction.

  1. Write the oxidation half-reaction for oxalate ion

Oxalate ion is oxidised to carbon dioxide as:

C2O42−→2CO2+2e−\mathrm{C_2O_4^{2-} \rightarrow 2CO_2 + 2e^-}C2​O42−​→2CO2​+2e−
  1. Balance electrons

To match electrons, multiply the oxalate half-reaction by 5 and the permanganate half-reaction by 2 if writing the full reaction. But the question asks only for the number of moles of H+\mathrm{H^+}H+ required by 1 mole of MnO4−\mathrm{MnO_4^-}MnO4−​.

From the permanganate half-reaction directly:

1 mol MnO4− requires 8 mol H+1\ \text{mol } \mathrm{MnO_4^-} \text{ requires } 8\ \text{mol } \mathrm{H^+}1 mol MnO4−​ requires 8 mol H+
  1. Check with full balanced reaction

The full balanced reaction in acidic medium is:

2MnO4−+5C2O42−+16H+→2Mn2++10CO2+8H2O\mathrm{2MnO_4^- + 5C_2O_4^{2-} + 16H^+ \rightarrow 2Mn^{2+} + 10CO_2 + 8H_2O}2MnO4−​+5C2​O42−​+16H+→2Mn2++10CO2​+8H2​O

So, per mole of MnO4−\mathrm{MnO_4^-}MnO4−​:

162=8\frac{16}{2} = 8216​=8

Thus, the number of moles of H+\mathrm{H^+}H+ required is 8.

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