Eo value for various ions are as follows :Eo(MnO4-) = +1.51 VE°(Ag/Ag+) = +0.7996 VEo(Au/Au+) = +1.692 VEo(Zn/Zn2+) = -0.761 VBased on this data, permaganate can be used to oxidize :

Permanganate can oxidise Zn and Ag.An oxidant can oxidise a metal when its reduction potential is higher than that of the metal ion/metal couple. Permanganate's couple is +1.51 V. The silver couple is +0.7996 V and the zinc couple -0.761 V, both lower, so MnO4- can oxidise both metals:\[ \begin{aligned} E^{o}_{cell}(\text{Ag}) &= 1.51 - 0.80 = +0.71\ \text{V} \\ E^{o}_{cell}(\text{Zn}) &= 1.51 + 0.76 = +2.27\ \text{V} \end{aligned} \]The gold couple, +1.692 V, is above +1.51 V, so for gold the cell potential would be negative and permanganate cannot oxidise it. Every option containing Au is wrong.

Electrochemistry and Ionic Equilibria Questions and Answers

Q: The pH of the mixture of 800 ml of 0.1 M HCl and 200 ml of 0.3 M NaOH is close to :

The pH is close to 1.70.\[ \begin{aligned} n(\text{H}^{+}) &= 0.800 \times 0.1 = 0.080\ \text{mol} \\ n(\text{OH}^{-}) &= 0.200 \times 0.3 = 0.060\ \text{mol} \\ \text{excess H}^{+} &= 0.020\ \text{mol in } 1.0\ \text{L} \end{aligned} \]\[ \text{pH} = -\log(0.020) = 1.70 \]The original 0.1 M HCl had pH 1.00, so 1.10 is too acidic once 0.060 mol of the acid has been neutralised. 13.3 would mean excess base, and 6.90 near-exact neutralisation, but the acid is in excess by 0.020 mol in the combined 1 L.

71.

E^o value for various ions are as follows :

E^o(MnO₄^-) = +1.51 V
E°(Ag/Ag⁺) = +0.7996 V
E^o(Au/Au⁺) = +1.692 V
E^o(Zn/Zn²⁺) = -0.761 V

Based on this data, permaganate can be used to oxidize :

A.Au, Ag, Zn
B.Au, Ag
C.Zn, Ag
D.Zn, Au

Exam Year(s)

MH SET - 2025, SET Exam - 2025,

Answer: C

Permanganate can oxidise Zn and Ag.

An oxidant can oxidise a metal when its reduction potential is higher than that of the metal ion/metal couple. Permanganate's couple is +1.51 V. The silver couple is +0.7996 V and the zinc couple -0.761 V, both lower, so MnO₄^- can oxidise both metals:

\[ \begin{aligned} E^{o}_{cell}(\text{Ag}) &= 1.51 - 0.80 = +0.71\ \text{V} \\ E^{o}_{cell}(\text{Zn}) &= 1.51 + 0.76 = +2.27\ \text{V} \end{aligned} \]

The gold couple, +1.692 V, is above +1.51 V, so for gold the cell potential would be negative and permanganate cannot oxidise it. Every option containing Au is wrong.

Discuss in Forum

72.

The pH of the mixture of 800 ml of 0.1 M HCl and 200 ml of 0.3 M NaOH is close to :

A.1.10
B.6.90
C.13.3
D.1.70

Exam Year(s)

MH SET - 2025, SET Exam - 2025,

Answer: D

The pH is close to 1.70.

\[ \begin{aligned} n(\text{H}^{+}) &= 0.800 \times 0.1 = 0.080\ \text{mol} \\ n(\text{OH}^{-}) &= 0.200 \times 0.3 = 0.060\ \text{mol} \\ \text{excess H}^{+} &= 0.020\ \text{mol in } 1.0\ \text{L} \end{aligned} \]

\[ \text{pH} = -\log(0.020) = 1.70 \]

The original 0.1 M HCl had pH 1.00, so 1.10 is too acidic once 0.060 mol of the acid has been neutralised. 13.3 would mean excess base, and 6.90 near-exact neutralisation, but the acid is in excess by 0.020 mol in the combined 1 L.

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