E° value for various ions are as follows : E°(MnO4-) = +1.51 V E°(Ag/Ag+) = +0.7996 V E°(Au/Au+) = +1.692 V E°(Zn/Zn2+) = -0.761 V Based on this data, permaganate can be used to oxidize :
Zn, Ag
An oxidising agent can oxidise a metal only if the overall cell potential is positive. Working with reduction potentials, permanganate will oxidise a metal whenever
\(E^{\circ}_{\mathrm{MnO_4^-}} > E^{\circ}_{\mathrm{M^{n+}/M}}\).
Permanganate sits at +1.51 V, so compare each metal against that figure.
Zinc, -0.761 V. Far below +1.51 V, so the difference is large and positive: \(1.51 - (-0.761) = +2.27\) V. Zinc is easily oxidised — it is a reactive, electropositive metal that gives up electrons readily.
Silver, +0.7996 V. Still below +1.51 V, giving \(1.51 - 0.80 = +0.71\) V. So silver is oxidised, though less vigorously than zinc.
Gold, +1.692 V. This lies above permanganate, so the cell potential would be \(1.51 - 1.692 = -0.18\) V — negative, and the reaction is not spontaneous. Gold is not oxidised by permanganate.
That result matches chemical experience: gold's nobility is precisely its resistance to oxidation, and dissolving it requires aqua regia, where the real work is done not by a stronger oxidant alone but by chloride complexation — forming [AuCl4]- pulls the effective potential down far enough to make the reaction go.
So permanganate oxidises zinc and silver but not gold, which rules out every option containing Au.
Hence permanganate can be used to oxidize Zn and Ag.
Similar Questions
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Which of the following statement is incorrect ?
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Important Questions from Thermodynamics
- Second law of thermodynamics states that
A. Energy flows from higher concentration to lower concentration.
B. Order becomes disorder during energy transformations.
C. The quality of energy degrades as it is transformed.
D. Degraded energy is entropy, dessipated as waste products or heat.
E. Enthalpy is wasted in energy transformation.
Choose the most appropriate answer from the options given below: Choose the Incorrect Statement:
1 For a system at equilibrium, chemical potential is same in all phases.
2 Gibb's free energy change is zero at equilibrium state of a system.
3 Gibb's free energy change is positive for reaction to occur spontaneously.
4 $\Delta G$ will become more negative with increasing temperature.- In a closed thermodynamic system, across its boundaries
Melting Point of pure ice is-
Which one among the following statements with reference to the properties of water is not correct?
