1
MCQ (Single Correct Answer)

AIPMT 2007

The equilibrium constants of the following are

N2 + 3H2 $$\rightleftharpoons$$ 2NH3;     K1

N2 + O2 $$\rightleftharpoons$$ 2NO;     K2

H2 + $${1 \over 2}$$O2 $$\rightleftharpoons$$ H2O;     K3

The equilibrium constant (K) of the reaction :

2NH3 + $${5 \over 2}$$ O2 $$\rightleftharpoons$$ 2NO + 3H2O will be
A
K2K33/K1
B
K2K3/K1
C
K23K3/K1
D
K1K33/K2

Explanation

2NH3 $$\rightleftharpoons$$ N2 + 3H2;     $${1 \over {{K_1}}}$$

N2 + O2 $$\rightleftharpoons$$ 2NO;     K2

3H2 + $${3 \over 2}$$O2 $$\rightleftharpoons$$ 3H2O;     (K3)3

By adding all equations, we get

2NH3 + $${5 \over 2}$$ O2 $$\rightleftharpoons$$ 2NO + 3H2O

$$ \therefore $$ K = $${{{K_2} \times {{\left( {{K_3}} \right)}^3}} \over {{K_1}}}$$
2
MCQ (Single Correct Answer)

AIPMT 2006

The hydrogen ion concentration of a 10$$-$$8 M, HCl aqueous solution at 298 K (Kw = 10$$-$$14) is
A
1.0 $$ \times $$ 10$$-$$8 M
B
1.0 $$ \times $$ 10$$-$$6 M
C
1.0525 $$ \times $$ 10$$-$$7 M
D
9.525 $$ \times $$ 10$$-$$8 M

Explanation

In HCl solution [H+] = 10-8 M

Also from water, [H+] = 10-7 M

$$ \therefore $$ Total [H+] = 10-8 M + 10-7 M

= 1.1 ×10–7 M

$$ \simeq $$ 1.0525 $$ \times $$ 10$$-$$7 M
3
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.
4
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 = $${{{P_{C{O_2}}}} \over {{P_{C{H_4}}} \times {{\left[ {{P_{{O_2}}}} \right]}^2}}}$$

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