Redox Reactions And Electrochemistry Ques 201
Question: $ C{u^{+}} $ ion is not stable in aqueous solution because of disproportionation reaction. $ E^{o} $ value for disproportionation of $ C{u^{+}} $ is (Given $ E_{C{u^{2+}}/C{u^{+}}}^{o}=0.15 $ , $ E_{C{u^{2+}}/Cu}^{o}=0.34V $ ) [IIT 1995]
Options:
A) - 0.49 V
B) 0.49 V
C) - 0.38 V
D) 0.38 V
Show Answer
Answer:
Correct Answer: D
Solution:
The required reaction $ (C{u^{++}}+Cu\to 2C{u^{+}}) $ can be obtained by using the following reactions.
$ C{u^{++}}+{e^{-}}\to C{u^{+}};,E_{C{u^{++}}/C{u^{+}}}^{o}=0.15V $ -..(i)
$ C{u^{++}}+2{e^{-}}\to Cu;E_{C{u^{++}}/Cu}^{o}=0.,34V, $ -..(ii)
Multiplying eq. (i) by 2 we get
$ 2C{u^{++}}+2{e^{-}}\to 2C{u^{+}} $ -..(iii)
$ \Delta G_1=-nFE=-2\times F\times 0.15 $
$ C{u^{++}}+2{e^{-}}\to Cu, $ -..(iv)
$ \Delta G_2=-nFE=-2\times F\times 0.34 $
Subtract the eq. (iv) from (iii)
$ C{u^{++}}+Cu\to 2C{u^{+}} $ $ \Delta G_3=-,nFE=-1\times F\times E^{o} $
Also $ \Delta G_3=\Delta G_1-\Delta G_2 $ $ -1FE^{o}=(-,2F\times 0.15)-(-,2F\times 0.34) $ $ E^{o}=-,0.38 $
This is the value for the reaction $ C{u^{++}}+Cu\to 2C{u^{+}} $
But the given reaction is just reverse of it \ $ {E_{cell}} $ for given reaction = + 0.38V.
