1

### AIPMT 2012 Prelims

Equimolar solutions of the following substances were prepared separately. Which one of these will record the highest pH value ?
A
BaCl2
B
AlCl3
C
LiCl
D
BeCl2

## Explanation

All of the given salts have same anion i.e., Cl which on hydrolysis gives HCl which is a strong acid.

Now, among the salts which have cation that gives a strongest base on hydrolysis of salt have the highest pH value. As Ba form Ba(OH)2 which is a stronger base thus, it results in the highest pH value.
2

### AIPMT 2012 Prelims

pH of a saturated solution of Ba(OH)2 is 12. The value of solubility product (Ksp) of Ba(OH)2 is
A
3.3 $\times$ 10$-$7
B
5.0 $\times$ 10$-$7
C
4.0 $\times$ 10$-$6
D
5.0$\times$ 10$-$6

## Explanation

Ba(OH)2 Ba2+ + 2OH
At equilibrium x 2x

pH = – log[H+]

12 = – log [H+]

$\Rightarrow$ [H+] = 10–12

As, [H+][OH ] = 10–14

10–12 [OH ] = 10–14

$\Rightarrow$ [OH ] = 10–2

As [OH ] = 2x = 10–2 then x = 5.0 × 10–3

Now, Ksp = [Ba2+][OH ]2

Ksp = (5 × 10–3) (10–2)2 = 5.0 × 10–7
3

### AIPMT 2011 Mains

In qualitative analysis, the metals of group I can be separated from other ions by precipitating them as chloride salts. A solution initially contains Ag+ and pb2+ at a concentration of 0.10 M. Aqueous HCl is added to this solution until the Cl$-$ concentration is 0.10 M. What will the concentrations of Ag+ and Pb2+ be at equilibrium ?

(Ksp for AgCl = 1.8 $\times$ 10$-$10, Ksp for PbCl2 = 1.7 $\times$ 10$-$5)
A
[Ag+] = 1.8 $\times$ 10$-$7 M, [Pb2+] = 1.7 $\times$ 10$-$6 M
B
[Ag+] = 1.8 $\times$ 10$-$11 M, [Pb2+] = 8.5 $\times$ 10$-$5 M
C
[Ag+] = 1.8 $\times$ 10$-$9 M, [Pb2+] = 1.7 $\times$ 10$-$3 M
D
[Ag+] = 1.8 $\times$ 10$-$11 M, [Pb2+] = 1.7 $\times$ 10$-$4 M

## Explanation

Ksp[AgCl] = [Ag+][Cl-]

$\Rightarrow$ [Ag+] = ${{1.8 \times {{10}^{ - 10}}} \over {{{10}^{ - 1}}}}$ = 1.8 $\times$ 10$-$9 M

Ksp[PbCl2] = [Pb2+][Cl-]2

$\Rightarrow$ [Pb2+] = ${{1.7 \times {{10}^{ - 5}}} \over {{{10}^{ - 1}} \times {{10}^{ - 1}}}}$ = 1.7 $\times$ 10$-$3 M
4

### AIPMT 2011 Prelims

Which of the following is least likely to behave as Lewis base?
A
H2O
B
NH3
C
BF3
D
OH$-$

## Explanation

The species which have a lone pair of electrons to donate or a negative charge on it can act as a Lewis base. Here, N atom in NH3 and O atom in H2O have lone pair of electrons available for donation. In OH the negative charge on it results in to behave it as a Lewis base. But BF3 is an electron deficient species thus, it is least likely to behave as Lewis base.