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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

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Class 12