1

### AIPMT 2010 Prelims

If pH of a saturated solution of Ba(OH)2 is 12, the value of its Ksp is
A
4.00 $\times$ 10$-$6 M3
B
4.00 $\times$ 10$-$7 M3
C
5.00 $\times$ 10$-$6 M3
D
5.00$\times$ 10$-$7 M3

## 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
2

### AIPMT 2009

Which of the following molecules acts as a Lewis acid?
A
(CH3)2O
B
(CH3)3P
C
(CH3)3N
D
(CH3)3B

## Explanation

CH3)3 B – is an electron deficient compound due to inclete octate of B, thus behave as a lewis acid.
3

### AIPMT 2009

The ionization constant of ammonium hydroxide is 1.77 $\times$ 10$-$5 at 298 K. Hydrolysis constant of ammonium chloride is
A
6.50 $\times$ 10$-$12
B
5.65 $\times$ 10$-$13
C
5.65 $\times$ 10$-$12
D
5.65 $\times$ 10$-$10

## Explanation

Ammonium chloride is a salt of weak base and strong acid. In this case hydrolysis constant Kh can be calculated as

Kh = ${{{K_w}} \over {{K_b}}}$ = ${{{{10}^{ - 14}}} \over {1.77 \times {{10}^{ - 5}}}}$ = 5.65 $\times$ 10$-$10
4

### AIPMT 2009

What is the [OH$-$] in the final solution prepared by mixing 20.0 mL of 0.050 M HCl with 30.0 mL of 0.10 M Ba(OH)2?
A
0.40 M
B
0.0050 M
C
0.12 M
D
0.10 M

## Explanation

Number of equivalents of H+ = 20.0 × 0.050 milliequivalents

= 1.0 milliequivalents

Number of equivalents of OH = 2 × 30.0 × 0.10

= 6.0 milliequivalents

$\therefore$ Equivalents of OH- left after neutralization

= 6 – 1 = 5 milliequivalents

Total volume after neutralization

= 20.0 + 30.0 mL

= 50 mL

[OH-] = ${5 \over {50}}$ = 0.1 M