Chapter 7: Equilibrium

Q11Written answer

Which of the following will produce a buffer solution when mixed in equal volumes?

(i) 0.1 mol $\mathbf{d}{{\mathbf{m}}^{\mathbf{3}}}$ $\mathbf{N}{{\mathbf{H}}_{\mathbf{4}}}\mathbf{OH}$ and 0.1 mol $\mathbf{d}{{\mathbf{m}}^{\mathbf{3}}}$HCl

(ii) 0.05 mol $\mathbf{d}{{\mathbf{m}}^{\mathbf{3}}}$ $\mathbf{N}{{\mathbf{H}}_{\mathbf{4}}}\mathbf{OH}$ and 0.1 mol $\mathbf{d}{{\mathbf{m}}^{\mathbf{3}}}$HCl

(iii) 0.1 mol $\mathbf{d}{{\mathbf{m}}^{\mathbf{3}}}$ $\mathbf{N}{{\mathbf{H}}_{\mathbf{4}}}\mathbf{OH}$ and 0.05 mol $\mathbf{d}{{\mathbf{m}}^{\mathbf{3}}}$HCl

(iv) 0.1 mol $\mathbf{d}{{\mathbf{m}}^{\mathbf{3}}}$ $\mathbf{C}{{\mathbf{H}}_{\mathbf{4}}}\mathbf{COONa}$ and 0.1 mol $\mathbf{d}{{\mathbf{m}}^{\mathbf{3}}}$NaOH

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Ans: When 0.1 mol $\text{d}{{\text{m}}^{\text{-3}}}\text{N}{{\text{H}}_{\text{4}}}\text{OH}$ and 0.05 mol $\text{d}{{\text{m}}^{\text{-3}}}$ HCl react total amount of HCl reacts with $\text{N}{{\text{H}}_{\text{4}}}\text{OH}$ to form $\text{N}{{\text{H}}_{\text{4}}}\text{Cl}$ and some $\text{N}{{\text{H}}_{\text{4}}}\text{OH}$ will be left unreacted. Thus, the resultant solution contains $\text{N}{{\text{H}}_{\text{4}}}\text{Cl}$ and $\text{N}{{\text{H}}_{\text{4}}}\text{OH}$ which will produce a buffer solution. Hence, option(iii) is the correct answer.

Q12Written answer

In which of the following solvents is silver chloride most soluble?

(i) 0.1 mol $\mathbf{d}{{\mathbf{m}}^{\mathbf{-3}}}$ $\mathbf{AgN}{{\mathbf{O}}_{\mathbf{3}}}$solution

(ii) 0.1 mol $\mathbf{d}{{\mathbf{m}}^{\mathbf{-3}}}$ HCl solution

(iii) ${{\mathbf{H}}_{\mathbf{2}\text{ }}}\mathbf{O}$

(iv) Aqueous ammonia

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Ans: Aqueous ammonia will absorb chloride ions and thus the equilibria will shift in forward direction and solubility of silver chloride will increase. Hence, option(iv) is the correct answer.

Q13Written answer

What will be the value of pH of 0.01 mol $\mathbf{d}{{\mathbf{m}}^{\mathbf{-3}}}$ $\mathbf{C}{{\mathbf{H}}_{\mathbf{3}}}\mathbf{COOH}$$({{\mathbf{K}}_{\mathbf{a}}}\text{ }=\text{ }\mathbf{1}.\mathbf{74}\text{ }\times \text{ }\mathbf{1}{{\mathbf{0}}^{\mathbf{5}}})$?

(i) 3.4

(ii) 3.6

(iii) 3.9

(iv) 3.0

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Worked solution

Ans: pH for weak acid is given by the following equation:

\[pH = \frac{1}{2}[pK_{a}-log {C}] \]

\[= 21 [-log(1.74 \times 10^{-5}) - log {0.01}]\]

\[=3.4\].

Hence, option(i) is the correct answer.

Q14Written answer

${{\mathbf{K}}_{\mathbf{a}}}$ for $\mathbf{C}{{\mathbf{H}}_{\mathbf{3}}}\mathbf{COOH}$is 1.8 × $\mathbf{1}{{\mathbf{0}}^{\mathbf{5}}}$and ${{\mathbf{K}}_{\mathbf{b}}}$ for $\mathbf{N}{{\mathbf{H}}_{\mathbf{4}}}\mathbf{OH}$ is 1.8 × $\mathbf{1}{{\mathbf{0}}^{\mathbf{5}}}$ . The pH of ammonium acetate will be-

(i) 7.005

(ii) 4.75

(iii) 7.0

(iv) Between 6 and 7

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Ans: The equation for weak acid and weak base is given as-

pH=7+21(p${{\text{K}}_{\text{a}}}$−p${{\text{K}}_{\text{b}}}$)

${{\text{K}}_{\text{a}}}$=1.8×$\text{1}{{\text{0}}^{\text{--5}}}$

p${{\text{K}}_{\text{a}}}$=−log (1.8×$\text{1}{{\text{0}}^{\text{--5}}}$) =5−log1.8 =4.744

p${{\text{K}}_{\text{b}}}$=−log (1.8×$\text{1}{{\text{0}}^{\text{--5}}}$) =4.744

pH=7+21(p${{\text{K}}_{\text{a}}}$−p${{\text{K}}_{\text{b}}}$) =7.

Hence, option(iii) is the correct answer.

Q15Written answer

Which of the following options will be correct for the stage of half completion of the reaction $\mathbf{A}\rightleftharpoons \mathbf{B}$.

(i) $\mathbf{\Delta }{{\mathbf{G}}^{\odot }}$=0

(ii) $\mathbf{\Delta }{{\mathbf{G}}^{\odot }}$> 0

(iii) $\mathbf{\Delta }{{\mathbf{G}}^{\odot }}$ < 0

(iv) $\mathbf{\Delta }{{\mathbf{G}}^{\odot }}$= –RT ln2

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Ans: At the stage of half completion of reaction [A] = [B]. Therefore, K = 1. Hence, $\text{ }\!\!\Delta\!\!\text{ }{{\text{G}}^{\odot }}$=0. Hence, option(i) is the correct answer.

Q16Written answer

On increasing the pressure, in which direction will the gas phase reaction proceed to re-establish equilibrium, is predicted by applying the Le Chatelier’s principle. Consider the reaction. ${{\mathbf{N}}_{\mathbf{2}}}\left( \mathbf{g} \right)\mathbf{+3}{{\mathbf{H}}_{\mathbf{2}}}\left( \mathbf{g} \right)\to \mathbf{2N}{{\mathbf{H}}_{\mathbf{3}}}\mathbf{(g)}$ (g) Which of the following is correct, if the total pressure at which the equilibrium is established, is increased without changing the temperature? (i) K will remain same

(ii) K will decrease

(iii) K will increase

(iv) K will increase initially and decrease when pressure is very high.

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Ans: Equilibrium constant K will remain same if temperature is not changed. Hence, option(i) is the correct answer.

Q17Written answer

What will be the correct order of vapour pressure of water, acetone, and ether at 30$^{\mathbf{{}^\circ }}\mathbf{C}$. Given that among these compounds, water has maximum boiling point and ether has minimum boiling point?

(i) Water < ether < acetone

(ii) Water < acetone < ether

(iii) Ether < acetone < water

(iv) Acetone < ether < water

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Worked solution

Ans: Greater the boiling point, lower will be the vapour pressure. Hence, option(ii) is the correct answer.

Q18Written answer

At 500 K, equilibrium constant, ${{\mathbf{K}}_{\mathbf{c}}}$, for the following reaction is 5. $\frac{\mathbf{1}}{\mathbf{2}}\text{ }{{\mathbf{H}}_{\mathbf{2}}}\text{ }\left( \mathbf{g} \right)+\frac{\mathbf{1}}{\mathbf{2}}{{\mathbf{I}}_{\mathbf{2}}}\left( \mathbf{g} \right)\to \mathbf{HI}\text{ }(\mathbf{g})$ .What would be the equilibrium constant Kc for the reaction $2\mathbf{HI}\text{ }(\mathbf{g})\to \text{ }{{\mathbf{H}}_{\mathbf{2}}}\text{ }\left( \mathbf{g} \right)+{{\mathbf{I}}_{\mathbf{2}}}\left( \mathbf{g} \right)$.

(i) 0.04

(ii) 0.4

(iii) 25

(iv) 2.5

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Worked solution

Ans: If the equation is multiplied by 2, the equilibrium constant for the new equation is the square of K it means we must do the square of 5 that is 25. Then and on reversing the reaction the value of the equilibrium constant is inversed means the value of K comes out to be 1/25= 0.04. Hence, option(i) is the correct answer.

Q19Written answer

In which of the following reactions, the equilibrium remains unaffected on addition of small amount of argon at constant volume?

$\left( \mathbf{i} \right)\text{ }{{\mathbf{H}}_{\mathbf{2}}}\text{ }\left( \mathbf{g} \right)+{{\mathbf{I}}_{\mathbf{2}}}\text{ }\left( \mathbf{g} \right)\rightleftharpoons \mathbf{2HI}\text{ }\left( \mathbf{g} \right)$

$\left( \mathbf{ii} \right)\text{ }\mathbf{PC}{{\mathbf{l}}_{\mathbf{5}}}\left( \mathbf{g} \right)\rightleftharpoons \mathbf{PC}{{\mathbf{l}}_{\mathbf{3}}}\left( \mathbf{g} \right)+\mathbf{C}{{\mathbf{l}}_{\mathbf{2}\text{ }}}\left( \mathbf{g} \right)$

$\left( \mathbf{iii} \right)\text{ }{{\mathbf{N}}_{\mathbf{2}}}\left( \mathbf{g} \right)+\mathbf{3}{{\mathbf{H}}_{\mathbf{2}}}\left( \mathbf{g} \right)\rightleftharpoons \mathbf{2N}{{\mathbf{H}}_{\mathbf{3}}}\left( \mathbf{g} \right)$

(iv) The equilibrium will remain unaffected in all the three cases.

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Worked solution

Ans: At constant volume equilibrium remains unaffected with the addition of inert gas. Hence, option(iv) is the correct answer.

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Multiple Choice Questions (Type-I)