1
MCQ (Single Correct Answer)

AIPMT 2006

Which of the following pairs constitutes a buffer?
A
HCl and KCl
B
HNO2 and NaNO2
C
NaOH and NaCl
D
HNO3 and NH4NO3

Explanation

HNO2 is a weak acid and NaNO2 is its salt thus these two constitute to form an acidic buffer.
2
MCQ (Single Correct Answer)

AIPMT 2006

For the reaction :
CH4(g) + 2O2(g) $$\rightleftharpoons$$ CO2(g) + 2H2O(l),
$$\Delta $$Hr = $$-$$ 170.8 kJ mol$$-$$1.
Which of the following statements is not true?
A
The reaction is exothermic.
B
At equilibrium, the concentrations of CO2(g) and H2O(l) are not equal.
C
The equilibrium constant for the reaction is given by Kp = $${{\left[ {C{O_2}} \right]} \over {\left[ {C{H_4}} \right]\left[ {{O_2}} \right]}}$$
D
Addition of CH4(g) or O2(g) at equilibrium will cause a shift to the right.

Explanation

Option C is incorrect as the value of KP given is wrong. It should have been

KP = $${{{P_{C{O_2}}}} \over {{P_{C{H_4}}} \times {{\left[ {{P_{{O_2}}}} \right]}^2}}}$$
3
MCQ (Single Correct Answer)

AIPMT 2005

Equilibrium constants K1 and K2 for the following equilibriam:


are related as
A
K2 = 1/K12
B
K2 = K12
C
K2 = 1/K1
D
K2 = K1/2

Explanation

NO(g) + O2(g) ⇌ NO2(g) ,    K1

Reverse the above equation

NO2(g) ⇌ NO(g) + O2(g),     $${1 \over {{K_1}}}$$

Multiply the above equation by 2, we get

NO2(g) ⇌ NO(g) + O2(g),    $${\left( {{1 \over {{K_1}}}} \right)^2} = {K_2}$$
4
MCQ (Single Correct Answer)

AIPMT 2005

At 25oC, the dissociation constant of a base, BOH, is 1.0 $$ \times $$ 10$$-$$12. The concentration of hydroxyl ions in 0.01 M aqueous solution of the base would be
A
1.0 $$ \times $$ 10$$-$$5 mol L$$-$$1
B
1.0 $$ \times $$ 10$$-$$6 mol L$$-$$1
C
2.0 $$ \times $$ 10$$-$$6 mol L$$-$$1
D
1.0 $$ \times $$ 10$$-$$7 mol L$$-$$1

Explanation

BOH B+ + OH-
Initially C 0 0
At equilibbrium C - C$$\alpha $$ C$$\alpha $$ C$$\alpha $$


[OH-] = C$$\alpha $$

$$ \Rightarrow $$ [OH-] = $$\sqrt {{K_b}C} $$

$$ \Rightarrow $$ [OH-] = $$\sqrt {1 \times {{10}^{ - 12}} \times {{10}^{ - 2}}} $$

= 1.0 $$ \times $$ 10$$-$$7 mol L$$-$$1

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