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1

AIPMT 2003

MCQ (Single Correct Answer)
In Haber process 30 litres of dihydrogen and 30 litres of dinitrogen were taken for reaction which yielded only 50% of the expected product. What will be the composition of gaseous mixture underthe aforesaid condition in the end ?
A
20 litres ammonia, 20 litres nitrogen, 20 litres hydrogen
B
10 litres ammonia, 25 litres nitrogen, 15 litres hydrogen
C
20 litres ammonia, 10 litres nitrogen, 30 litres hydrogen
D
20 litres ammonia, 25 litres nitrogen, 15 litres hydrogen

Explanation

Balanced chemical equation for Haber's process is as follows :

3H2 + N2 $$ \to $$ 2NH3

It is given that only 50% of the expected product is formed hence only 10 litre of NH3 is formed.

Therefore, composition of gaseous mixture at the end is as follows :

N2 used = 5 litres

N2 left = 30 L – 5 L = 25 L

H2 used = 15 litres,

H2 legt = 30 L – 15 L = 15 L

NH3 = 10 L
2

AIPMT 2003

MCQ (Single Correct Answer)
Which one of the following statements is not true?
A
Among halide ions, iodide is the most powerful reducing agent.
B
Fluorine is the only halogen that does not show a variable oxidation state.
C
HOCl is a stronger acid than HOBr.
D
HF is a stronger acid than HCl.

Explanation

F is more electronegative than Cl therefore HF bond is stronger than HCl and hence proton is not given off easily and hence HF is a weakest acid.
3

AIPMT 2003

MCQ (Single Correct Answer)
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 = $${{{K_2} \times {{\left( {{K_3}} \right)}^3}} \over {{K_1}}}$$
4

AIPMT 2002

MCQ (Single Correct Answer)
Solution of 0.1 N NH4OH and 0.1 N NH4Cl has pH 9.25. Then find out pKb of NH4OH
A
9.25
B
4.75
C
3.75
D
8.25

Explanation

NH4OH and NH4Cl constitute to form a basic buffer.

pOH = pKb + log $${{\left[ {Salt} \right]} \over {\left[ {Base} \right]}}$$

We know, pOH+ pH = 14 or pOH = 14 – pH

$$ \therefore $$ 14 - pH - $$\log {{\left[ {Salt} \right]} \over {\left[ {Base} \right]}}$$ = pKb

$$ \Rightarrow $$ 14 - 9.25 - $$\log {{0.1} \over {0.1}}$$ = pKb

$$ \Rightarrow $$ 14 – 9.25 – 0 = pKb

$$ \Rightarrow $$ pKb = 4.75

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