NCERT Class XI Chemistry Redox Reactions Solutions
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Question : 26
Total: 30
Using the standard electrode potentials, predict if the reaction between the following is feasible :
(a)F e ( a q ) 3 + I ( a q ) –
(b)A g ( a q ) + C u ( s )
(c)F e ( a q ) 3 + C u ( s )
(d)A g ( s ) F e ( a q ) 3 +
(e)B r 2 ( a q ) F e ( a q ) 2 +
(a)
(b)
(c)
(d)
(e)
Solution:
(a) The possible reaction between Fe3+(aq) and I–(aq) is
2 F e ( a q ) 3 + + 2 I ( a q ) – 2 F e ( a q ) 2 + + I 2 ( s )
The above redox reaction can be split into the following two half reactions,
Oxidation :2 I ( a q ) – I 2 ( s ) + 2 e – E ° oxi
Reduction :[ F e ( a q ) 3 + + e – → F e ( a q ) 2 + ] E ° red
Overall reaction :2 F e ( a q ) 3 + + 2 I ( a q ) – 2 F e ( a q ) 2 + + I 2 ( s )
Since the EMF for the above reaction is positive, therefore, the above reaction is feasible.
(b) The possible reaction between Ag+(aq) and Cu(s) is
C u ( s ) + 2 A g ( a q ) + C u ( a q ) 2 + + 2 A g ( s )
The above redox reaction can be split into the following two half reactions,
Oxidation :C u ( s ) C u ( a q ) 2 + + 2 e – E ° oxi
Reduction :[ A g ( a q ) + + e – → A g ( s ) ] E ° red
Overall reaction :C u ( s ) + 2 A g ( a q ) + C u ( a q ) 2 + + 2 A g ( s )
Since the EMF for the above reaction comes out to be positive, therefore, the above reaction is feasible.
(c) There are two probabilities for reaction between Cu andF e 3 + F e ( a q ) 3 + C u ( s )
(i)C u ( s ) + 2 F e ( a q ) 3 + C u ( a q ) 2 + + 2 F e ( a q ) 2 +
The above reaction can be split into the following two half reactions,
Oxidation :C u ( s ) C u ( a q ) 2 + + 2 e – E ° oxi
Reduction :[ F e ( a q ) 3 + + e – → F e ( a q ) 2 + ] E ° red
Overall reaction :C u ( s ) + 2 F e ( a q ) 3 + C u ( a q ) 2 + + 2 F e ( a q ) 2 +
Since the EMF for the above reaction is positive, therefore, the above reaction is feasible.
(ii) If the reaction betweenF e ( a q ) 3 + C u ( s )
3 C u ( s ) + 2 F e ( a q ) 3 + 3 C u ( a q ) 2 + + 2 F e ( s )
The EMF of the reaction comes out to be negative, i.e., –0.376 V
(– 0.34 V – 0.036 V) and hence, this reaction is not feasible.
(d) There are two possibilities for reaction between Ag andF e 3 +
(i) If the reaction occurs by following equation,
A g ( s ) + F e ( a q ) 3 + A g ( a q ) + + F e ( a q ) 2 +
The reaction can be split into the following two half reactions,
Oxidation :A g ( s ) A g ( a q ) + + e – E ° oxi
Reduction :F e ( a q ) 3 + + e – F e ( a q ) 2 + E ° red
Overall reaction :A g ( s ) + F e ( a q ) 3 + A g ( a q ) + + F e ( a q ) 2 +
Since the EMF for the above reaction is negative, therefore, the above reaction is not feasible.
(ii) The reaction betweenA g ( s ) F e ( a q ) 3 +
3 A g ( s ) + F e ( a q ) 3 + 3 A g ( a q ) + + F e ( s )
EMF of this reaction comes to be even more negative i.e., –0.836 V, and hence this redox reaction is also not feasible.
(e) The reaction betweenB r 2 ( a q ) F e ( a q ) 2 + B r 2 ( a q ) + 2 F e ( a q ) 2 + 2 B r ( a q ) – + 2 F e ( a q ) 3 +
The above reaction can be split into the following two half reactions.
Oxidation :[ F e ( a q ) 2 + → F e ( a q ) 3 + + e – ] E ° oxi
Reduction :B r 2 ( a q ) + 2 e – → 2 B r ( a q ) – E ° red
Overall reaction :2 F e ( a q ) 2 + + B r 2 ( a q ) 2 F e ( a q ) 3 + + 2 B r ( a q ) –
Since the EMF for the above reaction is positive, therefore, the above reaction is feasible.
The above redox reaction can be split into the following two half reactions,
Oxidation :
Reduction :
Overall reaction :
Since the EMF for the above reaction is positive, therefore, the above reaction is feasible.
(b) The possible reaction between Ag+(aq) and Cu(s) is
The above redox reaction can be split into the following two half reactions,
Oxidation :
Reduction :
Overall reaction :
Since the EMF for the above reaction comes out to be positive, therefore, the above reaction is feasible.
(c) There are two probabilities for reaction between Cu and
(i)
The above reaction can be split into the following two half reactions,
Oxidation :
Reduction :
Overall reaction :
Since the EMF for the above reaction is positive, therefore, the above reaction is feasible.
(ii) If the reaction between
The EMF of the reaction comes out to be negative, i.e., –0.376 V
(– 0.34 V – 0.036 V) and hence, this reaction is not feasible.
(d) There are two possibilities for reaction between Ag and
(i) If the reaction occurs by following equation,
The reaction can be split into the following two half reactions,
Oxidation :
Reduction :
Overall reaction :
Since the EMF for the above reaction is negative, therefore, the above reaction is not feasible.
(ii) The reaction between
EMF of this reaction comes to be even more negative i.e., –0.836 V, and hence this redox reaction is also not feasible.
(e) The reaction between
The above reaction can be split into the following two half reactions.
Oxidation :
Reduction :
Overall reaction :
Since the EMF for the above reaction is positive, therefore, the above reaction is feasible.
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