1

### AIPMT 2001

Standard electrode potentials are
Fe2+/Fe [Eo = $-$0.44] and
Fe3+/Fe2+[ Eo = 0.77];
If Fe2+, Fe3+ and Fe blocks are kept together, then
A
Fe3+ increases
B
Fe3+ decreases
C
Fe2+/Fe3+ remains unchanged
D
Fe2+ decreases.

## Explanation

The metals having higher negative values of their electrode potential can displace metals having lower values from their salt solutions.
2

### AIPMT 2000

For the disproportionation of copper
2Cu+  $\to$ Cu2+ + Cu, Eo is
(Given Eo for Cu2+/Cu is 0.34 V and
Eo for Cu2+/Cu+ is 0.15 V.)
A
0.49 V
B
$-$ 0.19 V
C
0.38 V
D
$-$0.38 V

## Explanation

Cu2+ + 2e $\to$ Cu; E°1 = 0.34 V .....(1)

Cu2+ + e $\to$ Cu+ ; E°2 = 0.15 V.....(2)

Cu+ + e $\to$ Cu; E°3 = ? .....(3)

$\therefore$ $\Delta$Go1 = -2$\times$0.34$\times$F

and $\Delta$Go2 = -1$\times$0.15$\times$F

and $\Delta$Go3 = -1$\times$E°3$\times$F

Also, $\Delta$Go1 = $\Delta$Go2 + $\Delta$Go3

$\Rightarrow$ -0.68F = -0.15F - E°3 $\times$ F

$\Rightarrow$ E°3 = 0 68 - 0 15 = 0 53 V

$\therefore$ E°cell = 0.53 - 0.15 = 0.38 V
3

### AIPMT 2000

Equivalent conductances of Ba2+ and Cl$-$ ions are 127 and 76 ohm$-$1 cm$-$1 eq$-$1 respectively. Equivalent conductance of BaCl2 at infinite dilution is
A
139.5
B
101.5
C
203
D
279

## Explanation

According to Kohlrausch’s law, the equivalent conductance of BaCl2 at infinite dilution,

$\lambda $$\infty of BaCl2 = {1 \over 2}$$\lambda $$\infty of Ba2+ + \lambda$$\infty$ of Cl-

$\Rightarrow$ $\lambda$$\infty$ of BaCl2 = ${1 \over 2} \times 127 + 76$ = 139 5