1

### AIPMT 2015

Which one of the following pairs of solution is not an acidic buffer ?
A
CH3COOH and CH3COONa
B
H2CO3 and Na2CO3
C
H3PO4 and Na3PO4
D
HClO4 and NaClO4

## Explanation

An acidic buffer is a mixture of a weak acid and its salt with a strong base. Among CH3COOH, H2CO3, H3PO4 and HClO4, the HClO4 is a strong acid while all other are weak acid thus, HClO4 and NaClO4 does not constitute to form an acidic buffer.
2

### AIPMT 2015

Aqueous solution of which of the following compounds is the best conductor of electric current ?
A
Hydrochloric acid, HCl
B
Ammonia, NH3
C
Fructose, C6H12O6
D
Acetic acid, C2H4O2

## Explanation

HCl completely dissociates to give H+ and Cl- ions, hence act as very good electrolyte. While others are non- electrolytes.
3

### AIPMT 2015

If the equilibrium constant for

N2(g) + O2(g) $\rightleftharpoons$ 2NO(g) is K, the equilibrium

constant for

${1 \over 2}$ N2(g) + ${1 \over 2}$O2(g) $\rightleftharpoons$ NO(g) will be
A
${1 \over 2}$ K
B
K
C
K2
D
K1/2

## Explanation

When a reaction is divided by factor n then the new equilibrium constant of the reaction will be $\root n \of K$ .

Thus, here the given reaction is multiplied by factor ${1 \over 2}$ then the new equilibrium constant will be ${K^{{1 \over 2}}}$ .
4

### AIPMT 2015

What is the pH of the resulting solution when equal volumes of 0.1 M NaOH and 0.01 M HCl are mixed?
A
2.0
B
7.0
C
1.04
D
12.65

## Explanation

HCl + NaOH $\to$ NaCl + H2O
Initial  0.01       0.1            0          0
Final     0         0.09          0.01     0.01

As equal volumes of HCl and NaOH are added so the volume of resulting solution becomes double and the concentration of the solution becomes half.

$\therefore$ [OH-] = ${{0.09} \over 2}$ = 0.045 M

$\therefore$ pOH = – log[OH ] = –log [0.045] = 1.35

$\therefore$ pH = 14 – pOH = 14 – 1.35 = 12.65