1

AIPMT 2008

On the basis of the following Eo values, the strongest oxidizing agent is
[Fe(CN)6]4$-$ $\to$ [Fe(CN)6]3$-$ + e$-$;  Eo = $-$0.35 V

Fe2+ $\to$ Fe3+ + e$-$;  Eo = $-$0.77 V
A
Fe3+
B
[Fe(CN)6]3$-$
C
[Fe(CN)6]4$-$
D
Fe2+

Explanation

Substances which have higher reduction potential are stronger oxidizing agent.

[Fe(CN)6]4$-$ $\to$ [Fe(CN)6]3$-$ + e$-$;  Eo = $-$0.35 V

Fe2+ $\to$ Fe3+ + e$-$;  Eo = $-$0.77 V

Higher the +ve reduction potential, stronger will be the oxidising agent. Oxidising agent oxidises other compounds and gets itself reduced easily.
2

AIPMT 2007

The efficiency of a fuel cell is given by
A
$\Delta$G/$\Delta$S
B
$\Delta$G/$\Delta$H
C
$\Delta$S/$\Delta$G
D
$\Delta$H/$\Delta$G

Explanation

Efficiency of a fuel cell ($\phi$) = ${{\Delta G} \over {\Delta H}} \times 100$

Generally, fuel cells are expected to have an efficiency of 100 percent.
3

AIPMT 2007

The equilibrium constant of the reaction:
Cu(s) + 2Ag+(aq) $\to$ Cu2+(aq) + 2Ag(s);
Eo = 0.46 V at 298 K is
A
2.0 $\times$ 1010
B
4.0 $\times$ 1010
C
4.0 $\times$ 1015
D
2.4 $\times$ 1010

Explanation

RT ln K = nFE°

ln K = ${{nFE^\circ } \over {RT}}$

= ${{2 \times 0.46} \over {0.0591}}$

$\Rightarrow$ K = 4 $\times$ 1015
4

AIPMT 2006

A hypothetical electrochemical cell is shown below.

$A\left| {{A^ + }\left( {xM} \right)} \right|\left| {{B^ + }\left( {yM} \right)} \right|B$

The emf measured is + 0.20 V. The cell reaction is
A
A + B+ $\to$ A+ + B
B
A+ + B $\to$ A + B+
C
A+ + e$-$ $\to$ A;  B+ + e$-$ $\to$ B
D
the cell reaction cannot be predicted.

Explanation

From the given expression:

At anode : A $\to$ A+ + e

At cathode : B+ + e $\to$ B

Overall reaction is : A + B+ $\to$ A+ + B