Question

The standard reduction potentials of $Mg , Zn , Ni , H _{2}, Cu$ and $Ag$ are $-2.37,-0.76,-0.25,0.00,0.034 $ and $0.80$ volt respectively. Which one of the following cells has maximum voltage?

• A. $Mg +2 Ag ^{+} \rightarrow Mg ^{2+}+2 Ag$
• B. $Cu ^{2+}+ H _{2} \rightarrow Cu +2 H ^{+}$
• C. $Ni + Cu ^{2+} \rightarrow Ni ^{2+}+ Cu$
• D. $Zn +2 Ag ^{+} \rightarrow Zn ^{2+}+2 Ag$

Answer 1

Answer: (A)

$ Mg +2 Ag ^{+} \rightarrow Mg ^{2+}+2 Ag$

$E_{ cell }^{\circ}=E_{c}-E_{a}=0.80-(-2.37)=+3.17 V$

$Cu ^{2+}+ H _{2} \rightarrow Cu +2 H ^{+}$

$E_{ cell }^{\circ}=0.034-0=+0.034 V$

$Ni + Cu ^{2+} \rightarrow Ni ^{2+}+ Cu$

$E_{ cell }^{\circ}=0.034-(-0.25)=0.284 V$

$Zn +2 Ag ^{+} \rightarrow Zn ^{2+}+2 Ag$

$E_{ cell }^{\circ}=0.80-(-0.76 V )=1.56 V$