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Ellingham Diagram

Zinc, cadmium...

Question

Zinc, cadmium and mercury are found in nature as sulphides. Values of standard reduction potentials for the half-reactions are :
$M^{2 +} (a q) + 2 e^{-} \to M (s)$
$\begin{matrix} M & E^{\circ} Z n & - 0.76 V C d & - 0.40 V H g & + 0.79 V \end{matrix}$ .
Which sulphides give element not oxide on roasting?

Z n S

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H g S

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C d S

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None of these

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Solution

The correct option is B $H g S$
$Δ G = - n E^{o} F$

$For the reduction to be favourable, Δ G must be -ve. So, E^{o} should be positive$ .
The highest positive value will be the most favourable to reduce to metal from the sulphide.

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Similar questions

Z n | Z n^{2 +} (a q) (1.0 M) | | C u^{2 +} (a q) (1.0 M) | C u

+ 0.35 V

2 e^{-} + C u^{2 +} (a q) \to C u^{2 +} (a q) (1.0 M) | C u

+ 0.35 V

2 e^{-} + C u^{2 +} (a q) \to C u

- 0.763 V

2 e^{-} + Z n^{2 +} (a q) \to Z n

Z n \to Z n^{+ +} + 2 e^{-}, E^{0} = 0.76 V

C u \to C u^{+ +} + 2 e^{-}, E^{0} = 0.34 V

Z n^{2 +} (a q) + 2 e ⇌ Z n (s) - 0.762

C r^{3 +} (a q) + 2 e ⇌ C r (s) - 0.740

2 H^{+} (a q) + 2 e ⇌ H_{2} (g) 0.000

F e^{3 +} (a q) + 2 e ⇌ F e^{2 +} (a q) 0.770

The standard oxidation potential of zinc and silver in water at 298 K are

Which of the following reactions actually take place

Z n^{2 +} (a q .) + 2 e ⇌ Z n (s); - 0.762

C r^{3 +} (a q) + 3 e ⇌ C r (s); - 0.740

2 H^{+} (a q) + 2 e ⇌ H_{2} (g); 0.00

F e^{3 +} (a q) + e ⇌ F e^{2 +} (a q); 0.770

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