Which of the following reactions will not take place at cathode?

A g^{+} \to A g - e^{-}

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F e^{2 +} \to F e^{3} + + e^{-}

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C u^{2 +} + 2 e^{-} \to C u

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A l^{3 +} \to A l - 3 e^{-}

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Solution

The correct option is B $F e^{2 +} \to F e^{3} + + e^{-}$
In a electrochemical cell, anode is the electrode where oxidation takes place and cathode is the electrode where reduction takes place.
A. $A g^{+} \to A g - e^{-}$ can be written as:
$A g^{+} + e^{-} \to A g$ : gain of electron=Reduction i.e at cathode
B. $F e^{2 +} \to F e^{3 +} + e^{-}$ : loss of electron=Oxidation i.e. at anode
C. $C u^{2 +} + 2 e^{-} \to C u$ : gain of electron=Reduction i.e at cathode
D. $A l^{3 +} \to A l - 3 e^{-}$ can be written as:
$A l^{3 +} + 3 e^{-} \to A l$ : gain of electron=Reduction i.e at cathode
Among the given reactions $F e^{2 +} \to F e^{3 +} + e^{-}$ is an oxidation reaction and thus will not take place at cathode.

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Similar questions

The oxidation and reduction half reactions of the reaction

2Al_(s) + 3Cu²⁺_(aq) → 2Al³⁺_(aq) + 3Cu_(s) are

Q. Find the

△ G^{\circ}

of a galvanic cell with

A g

and

A l

Standard Reduction Potentials at

25^{\circ} C

Half-Reaction	$E^{\circ} (V)$
$F_{2} + 2 e^{-} \to 2 F^{-}$	$2.87$
$A g^{2} + e^{-} \to A g^{+}$	$1.99$
$C o^{3 +} + e^{-} \to C o^{2 +}$	$1.82$
$H_{2} O_{2} + 2 H^{+} + 2 e^{-} \to 2 H_{2} O$	$1.78$
$M n O_{4}^{-} + 4 H^{+} + 3 e^{-} \to M n O_{2} + 2 H_{2} O$	$1.68$
$2 e^{-} + 2 H^{+} + I O_{4}^{-} \to I O_{3}^{-} + H_{2} O$	$1.60$
$M n O_{4}^{-} + 8 H^{+} + 5 e^{-} \to M n^{2 +} + 4 H_{2} O$	$1.51$
$A u^{3 +} + 3 e^{-} \to A u$	$1.50$
$C l_{2} + 2 e^{-} \to 2 C l^{-}$	$1.36$
$O_{2} + 4 H^{+} + 4 e^{-} \to 2 H_{2} O$	$1.23$
$M n O_{2} + 4 H^{+} + 2 e^{-} \to M n^{2 +} + 2 H_{2} O$	$1.21$
$B r_{2} + 2 e^{-} \to 2 B r^{-}$	$1.09$
$N O_{3}^{-} + 4 H^{+} + 3 e^{-} \to N O + 2 H_{2} O$	$0.96$
$C l O_{2} + e^{-} \to C l O_{2}$	$0.954$
$2 H g^{2 +} + 2 e^{-} \to H g_{2}^{2 +}$	$0.91$
$A g^{+} + e^{-} \to A g$	$0.80$
$H g_{2}^{2 +} + 2 e^{-} \to 2 H g$	$0.80$
$F e^{3 +} + e^{-} \to F e^{2 +}$	$0.77$
$O_{2} + 2 H^{+} + 2 e^{-} \to H_{2} O_{2}$	$0.68$
$M n O_{4}^{-} + e^{-} \to M n O_{4}^{2 -}$	$0.56$
$I_{2} + 2 e^{-} \to 2 I^{-}$	$0.54$
$C u^{+} + e^{-} \to C u$	$0.52$
$O_{2} + 2 H_{2} O + 4 e^{-} \to 4 O H^{-}$	$0.40$
$C u^{2 +} + 2 e^{-} \to C u$	$0.34$
$A g C l + e^{-} \to A g + C l^{-}$	$0.22$
$C u^{2 +} + e^{-} \to C u^{+}$	$0.16$
$2 H^{+} + 2 e^{-} \to H_{2}$	$0.00$
$F e^{3 +} + 3 e^{-} \to F e$	$- 0.036$
$P b^{2 +} + 2 e^{-} \to P b$	$- 0.13$
$N i^{2 +} + 2 e^{-} \to N i$	$- 0.23$
$C d^{2 +} + 2 e^{-} \to C d$	$- 0.40$
$F e^{2 +} + 2 e^{-} \to F e$	$- 0.44$
$C r^{3 +} + e^{-} \to C r^{2 +}$	$- 0.50$
$C r^{3 +} + 3 e^{-} \to C r$	$- 0.73$
$Z n^{2 +} + 2 e^{-} \to Z n$	$- 0.76$
$2 H_{2} O + 2 e^{-} \to H_{2} + 2 O H^{-}$	$- 0.83$
$M n^{2 +} + 2 e^{-} \to M n$	$- 1.18$
$A l^{3 +} + 3 e^{-} \to A l$	$- 1.66$
$H_{2} + 2 e^{-} \to 2 H^{-}$	$- 2.23$
$M g^{2 +} + 2 e^{-} \to M g$	$- 2.37$
$N a^{+} + e^{-} \to N a$	$- 2.71$
$C a^{2 +} + 2 e^{-} \to C a$	$- 2.76$
$B a^{2 +} + 2 e^{-} \to B a$	$- 2.90$
$K^{+} + e^{-} \to K$	$- 2.92$
$L i^{+} + e^{-} \to L i$	$- 3.05$

Q. Rank the following elements by increasing ease of oxidation with most easily oxidized LAST:

C d, C u, N i, F e

Standard Reduction Potentials at

25^{\circ} C

Half-Reaction	$E^{\circ} (V)$
$F_{2} + 2 e^{-} \to 2 F^{-}$	$2.87$
$A g^{2} + e^{-} \to A g^{+}$	$1.99$
$C o^{3 +} + e^{-} \to C o^{2 +}$	$1.82$
$H_{2} O_{2} + 2 H^{+} + 2 e^{-} \to 2 H_{2} O$	$1.78$
$M n O_{4}^{-} + 4 H^{+} + 3 e^{-} \to M n O_{2} + 2 H_{2} O$	$1.68$
$2 e^{-} + 2 H^{+} + I O_{4}^{-} \to I O_{3}^{-} + H_{2} O$	$1.60$
$M n O_{4}^{-} + 8 H^{+} + 5 e^{-} \to M n^{2 +} + 4 H_{2} O$	$1.51$
$A u^{3 +} + 3 e^{-} \to A u$	$1.50$
$C l_{2} + 2 e^{-} \to 2 C l^{-}$	$1.36$
$O_{2} + 4 H^{+} + 4 e^{-} \to 2 H_{2} O$	$1.23$
$M n O_{2} + 4 H^{+} + 2 e^{-} \to M n^{2 +} + 2 H_{2} O$	$1.21$
$B r_{2} + 2 e^{-} \to 2 B r^{-}$	$1.09$
$N O_{3}^{-} + 4 H^{+} + 3 e^{-} \to N O + 2 H_{2} O$	$0.96$
$C l O_{2} + e^{-} \to C l O_{2}$	$0.954$
$2 H g^{2 +} + 2 e^{-} \to H g_{2}^{2 +}$	$0.91$
$A g^{+} + e^{-} \to A g$	$0.80$
$H g_{2}^{2 +} + 2 e^{-} \to 2 H g$	$0.80$
$F e^{3 +} + e^{-} \to F e^{2 +}$	$0.77$
$O_{2} + 2 H^{+} + 2 e^{-} \to H_{2} O_{2}$	$0.68$
$M n O_{4}^{-} + e^{-} \to M n O_{4}^{2 -}$	$0.56$
$I_{2} + 2 e^{-} \to 2 I^{-}$	$0.54$
$C u^{+} + e^{-} \to C u$	$0.52$
$O_{2} + 2 H_{2} O + 4 e^{-} \to 4 O H^{-}$	$0.40$
$C u^{2 +} + 2 e^{-} \to C u$	$0.34$
$A g C l + e^{-} \to A g + C l^{-}$	$0.22$
$C u^{2 +} + e^{-} \to C u^{+}$	$0.16$
$2 H^{+} + 2 e^{-} \to H_{2}$	$0.00$
$F e^{3 +} + 3 e^{-} \to F e$	$- 0.036$
$P b^{2 +} + 2 e^{-} \to P b$	$- 0.13$
$N i^{2 +} + 2 e^{-} \to N i$	$- 0.23$
$C d^{2 +} + 2 e^{-} \to C d$	$- 0.40$
$F e^{2 +} + 2 e^{-} \to F e$	$- 0.44$
$C r^{3 +} + e^{-} \to C r^{2 +}$	$- 0.50$
$C r^{3 +} + 3 e^{-} \to C r$	$- 0.73$
$Z n^{2 +} + 2 e^{-} \to Z n$	$- 0.76$
$2 H_{2} O + 2 e^{-} \to H_{2} + 2 O H^{-}$	$- 0.83$
$M n^{2 +} + 2 e^{-} \to M n$	$- 1.18$
$A l^{3 +} + 3 e^{-} \to A l$	$- 1.66$
$H_{2} + 2 e^{-} \to 2 H^{-}$	$- 2.23$
$M g^{2 +} + 2 e^{-} \to M g$	$- 2.37$
$N a^{+} + e^{-} \to N a$	$- 2.71$
$C a^{2 +} + 2 e^{-} \to C a$	$- 2.76$
$B a^{2 +} + 2 e^{-} \to B a$	$- 2.90$
$K^{+} + e^{-} \to K$	$- 2.92$
$L i^{+} + e^{-} \to L i$	$- 3.05$

Q. Which of the following metals or metal ions will be reduced by

F e

A g^{+} (a q) + e^{-} - > A g (s) E^{\circ} = + 0.80 V

C u^{2 +} (a q) + 2 e^{-} - - > C u (s) E^{\circ} = + 0.34 V

P b^{2 +} (a q) + 2 e^{-} - - > P b (s) E^{\circ} = - 0.13 V

F e^{2 +} (a q) + 2 e^{-} - - > F e (s) E^{\circ} = - 0.44 V

A l^{3 +} (a q) + 3 e^{-} - - > A l (s) E^{\circ} = - 1.66 V

Given: $F e_{(s)} \to F e^{2 +} + 2 e^{-}; E^{o} = + 0.44 V$

$P b_{(s)} \to P b^{2 +} + 2 e^{-}; E^{o} = + 0.13 V$

$A g^{+} e^{-} \to A g; E^{o} = + 0.8 V$

$C u^{2 +} 2 e^{-} \to C u; E^{o} = + 0.34 V$

Which of the following metals will oxidise iron?

a) $A g$

b) $C u$

c) $P b$

d) None of these

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