1

### AIPMT 2010 Mains

Consider the following relations for emf of an electrochemical cell
(i)   EMF of cell = (Oxidation potential of anode) $-$ (Reduction potential of cathode)
(ii)  EMF of cell = (Oxidation potential of anode) + (Reduction potential of cathode)
(iii) EMF of cell = (Reductional potential of anode) + (Reduction potential of cathode)
(iv) EMF of cell = (Oxidation potential of anode) $-$ (Oxidation potential of cathode)

Which of the above relations are correct?
A
(iii) and (i)
B
(i) and (ii)
C
(iii) and (iv)
D
(ii) and (iv)

## Explanation

EMF of a cell = Reduction potential of cathode – Reduction potential of anode

= Reduction potential of cathode + Oxidation potential of anode

= Oxidation potential of anode – Oxidation potential of cathode.
2

### AIPMT 2010 Prelims

An increase in equivalent conductance of a strong electrolyte with dilution is mainly due to
A
increase in ionic mobility of ions
B
100% ionisation of electrolyte at normal dilution
C
increase in both i.e., number of ions and ionic mobility of ions
D
increase in number of ions.

## Explanation

Dilution of strong electrolytes increases ionisation, hence ionic mobility of ions increases which in turn increases equivalent conductance of the solution.
3

### AIPMT 2010 Mains

Which of the following expressions correctly represents the equivalent conductance at infinite diluation of Al2(SO4)3. Given that $\mathop \Lambda \limits^ \circ$Al3+ and $\mathop \Lambda \limits^ \circ$so$_4^{2 - }$ are the equivalent conductances at infinite dilution of the respective ions?
A
$2\mathop \Lambda \limits^ \circ$Al3+   +   $3\mathop \Lambda \limits^ \circ$so$_4^{2 - }$
B
$\mathop \Lambda \limits^ \circ$Al3+   +   $\mathop \Lambda \limits^ \circ$so$_4^{2 - }$
C
($\mathop \Lambda \limits^ \circ$Al3+   +   $\mathop \Lambda \limits^ \circ$so$_4^{2 - }$) $\times$ 6
D
${1 \over 3}$$\mathop \Lambda \limits^ \circ Al3+ + {1 \over 2}$$\mathop \Lambda \limits^ \circ$so$_4^{2 - }$

## Explanation

Equivalent conductance of an electrolyte at infinite dilution is given by the sum of equivalent conductances of the respective ions at infinite dilution.
4

### AIPMT 2010 Prelims

For the reduction of silver ions with copper metal, the standard cell potential was found to be + 0.46 V at 25oC. The value of standard Gibb's energy, $\Delta$Go will be
(F = 96500 C mol$-$1)
A
$-$ 89.0 kJ
B
$-$ 89.0 J
C
$-$ 44.5 kJ
D
$-$ 98.0 kJ

## Explanation

The cell reaction

Cu + 2Ag+ $\to$ Cu2+ + 2Ag

We know, $\Delta$G° = – nFE°cell

= – 2 × 96500 × 0.46 = – 88780 J

= – 88.780 kJ = – 89 kJ