NCERT Class XII Chemistry
Chapter - Electrochemistry
Questions with Solutions
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Question : 17
Total: 32
Using the standard electrode potentials predict if the reaction between the following is feasible:
(i)F e 3 + ( a q ) and I – ( a q )
(ii)A g + ( a q ) and C u ( s )
(iii)F e 3 + ( a q ) and B r – ( a q )
(iv)A g ( s ) and F e 3 + ( a q )
(v)B r 2 ( a q ) and F e 2 + ( a q )
Given :E ° 1 ⁄ 2 I 2 ∕ I – = 0.54 V ,
E ° C u 2 + ∕ C u = 0.34 V ,
E ° 1 ⁄ 2 B r 2 ∕ B r – = 1.09 V ,
E ° A g + ∕ A g = 0.80 V ,
E ° F e 3 + ∕ F e 2 + = 0.77 V
(i)
(ii)
(iii)
(iv)
(v)
Given :
Solution:
A reaction is feasible if EMF of the cell reaction is positive.
(i) F e 3 + ( a q ) + I − ( a q ) → F e 2 + ( a q ) +
I 2
i . e . , P t | I 2 | I − ( a q ) | | F e 3 + ( a q ) | F e 2 + ( a q ) | P t
∴ E ° c e l l = E ° F e 3 + ∕ F e 2 + – E ° 1 ∕ 2 I 2 ∕ I –
= 0.77 – 0.54 = 0.23 V ( )
i . e . , C u | C u 2 + ( a q ) | | A g + ( a q ) | A g
E ° c e l l = E ° A g + ∕ A g – E ° C u 2 + ∕ C u
= 0.80 – 0.34 = 0.46 V ( )
i . e . , B r 2 | B r − ( a q ) | | F e 3 + ( a q ) | F e 2 + ( a q )
E ° c e l l = E ° F e 3 + ∕ F e 2 + – E ° 1 ∕ 2 B r 2 ∕ B r –
= 0.77 – 1.09 = – 0.32 V
i . e . , A g ( s ) | A g + ( a q ) | | A g 3 + ( a q ) | A g 2 + ( a q )
E ° c e l l = E ° F e 3 + ∕ F e 2 + – E ° A g + ∕ A g
= 0.77 – 0.80 = – 0.03 V
i . e . , F e 2 + ( a q ) | F e 3 + ( a q ) | | B r 2 | B r –
E ° c e l l = E ° 1 ∕ 2 B r 2 ∕ B r – – E ° F e 3 + ∕ F e 2 +
= 1.09 – 0.77 = 0.32 V
(i)
(ii) A g + ( a q ) + C u ( s ) – – – – – – ▶ A g ( s ) + C u 2 + ( a q ) ,
(iii) F e 3 + ( a q ) + B r − ( a q ) – – – – – – ▶ F e 2 + ( a q ) +
B r 2 ,
(iv)A g ( s ) + F e 3 + ( a q ) – – – – – – ▶ A g + ( a q ) + F e 2 + ( a q )
(v)
B r 2 ( a q ) + F e 2 + ( a q ) – – – – – – ▶ B r − ( a q ) + F e 2 + ( a q ) ,
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