Question

$\text {For\ the\ disproportionation\ of \ copper:}$ $2Cu+→Cu^{+2}+Cu$, $Eº$ $\text {is:}$
$(\text {Given \ Eº \ for }\ Cu^{+2}/Cu \ \text {is}\ 0.34\ V\ \text { and\ Eº \ for} \ Cu^{+2}/Cu^+\ \text { is}\ 0.15\ V)$

• A. $0.49\ V$
• B. $-0.19\ V$
• C. $0.38\ V$
• D. $-0.38\ V$

Answer 1

Answer: (C)

$0.38\ V$

Answer 2

$\text {Cell\ reaction \ is:}$
$Cu ^++ e^−→Cu$
$\text {To \ calculate\ the\ value\ of}$ $E_0$ $for$ $Cu^+/Cu$
$−nFE_{Cu+/Cu} = [(−nFE_{Cu2+/Cu}) + (−nFE_{Cu+/Cu^{2+}})]$
$\text {On \ substituting\ the \ values:}$
⇒$−1×F×E_{Cu+/Cu}=[(−2×0.34)+(−1)×(−0.15)]$
So, $E_0$ for $Cu^+/Cu$ $= 0.53\ V$
$\text {The\ reactions\ at \ the\ cell \ are:}$
$Cu^+ →Cu^{+2} \+ e$
$E_0 \ for \ Cu^{+ 2}/Cu^+=−0.15V$
$Cu^++e→Cu$
$E_0\ for\ Cu^+/Cu = 0.53\ V$
$\text {Total \ reaction:}$ $2Cu^+ →Cu^{+2} \+ Cu$
$E_{cell} = E_{Cu^+/Cu^{2+}} + E_{Cu^+/Cu}$
$E_{cell} = −0.15\ V+0.53\ V$
$E_cell =0.38\ V$

$\text {So, \ the\ correct\ option \ is\ (C):}$ $0.38\ V$