CBSE Class 11 Chemistry Chemical Equilibrium Assignment

Question. Find out the solubility of Ni(OH)₂ in 0.1 M NaOH.
Given that the ionic product of Ni(OH)₂ is 2 × 10^–15.
(a) 2 × 10^–13 M
(b) 2 × 10^–8 M
(c) 1 × 10^–13 M
(d) 1 × 10⁸ M
Answer. A

Question. The pH of 0.01 M NaOH_(aq) solution will be
(a) 7.01
(b) 2
(c) 12
(d) 9
Answer. C

Question. The percentage of pyridine (C₅H₅N) that forms pyridinium ion (C₅H₅N + H) in a 0.10 M aqueous pyridine solution (Kb for C₅H₅N = 1.7 × 10^–9) is
(a) 0.0060%
(b) 0.013%
(c) 0.77%
(d) 1.6% 
Answer. B

Question. 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
Answer. D

Question. Which of the following salts will give highest pH in water?
(a) KCl
(b) NaCl
(c) Na₂CO₃
(d) CuSO₄
Answer. C

Question. Accumulation of lactic acid (HC₃H₅O₃), a monobasic acid in tissues leads to pain and a feeling of fatigue. In a 0.10 M aqueous solution, lactic acid is 3.7% dissociated. The value of dissociation constant,Ka, for this acid will be
(a) 1.4 × 10^–5
(b) 1.4 × 10^–4
(c) 3.7 × 10^–4
(d) 2.8 × 10^–4
Answer. B

Question. At 100°C the Kw of water is 55 times its value at 25°C. What will be the pH of neutral solution?
(log 55 = 1.74)
(a) 7.00
(b) 7.87
(c) 5.13
(d) 6.13
Answer. D

Question. Equimolar solutions of the following substances were prepared separately. Which one of these will record the highest pH value?
(a) BaCl₂
(b) AlCl₃
(c) LiCl
(d) BeCl₂ 
Answer. A

Question. What is [H+] in mol/L of a solution that is 0.20 M in CH₃COONa and 0.10 M in CH₃COOH?
(Ka for CH₃COOH = 1.8 × 10^–5)
(a) 3.5 × 10^–4
(b) 1.1 × 10^–5
(c) 1.8 × 10^–5
(d) 9.0 × 10^–6
Answer. D

Question. The ionization constant of ammonium hydroxide is 1.77 × 10^–5 at 298 K. Hydrolysis constant of ammonium chloride is
(a) 6.50 × 10^–12
(b) 5.65 × 10^–13
(c) 5.65 × 10^–12
(d) 5.65 × 10^–10
Answer. D

Question. What is the [OH^–] in the final solution prepared by mixing 20.0 mL of 0.050 M HCl with 30.0 mL of 0.10 M Ba(OH)₂?
(a) 0.40 M
(b) 0.0050 M
(c) 0.12 M
(d) 0.10 M
Answer. D

Question. Equal volumes of three acid solutions of pH 3, 4 and 5 are mixed in a vessel. What will be the H⁺ ion concentration in the mixture?
(a) 3.7 × 10^–3 M
(b) 1.11 × 10^–3 M
(c) 1.11 × 10^–4 M
(d) 3.7 × 10^–4 M
Answer. D

Question. A weak acid, HA, has a Ka of 1.00 × 10^–5. If 0.100 mol of this acid is dissolved in one litre of water, the percentage of acid dissociated at equilibrium is closest to
(a) 1.00%
(b) 99.9%
(c) 0.100%
(d) 99.0% 
Answer. A

Question. Calculate the pOH of a solution at 25°C that contains 1 × 10^–10 M of hydronium ions, i.e. H₃O⁺.
(a) 4.000
(b) 9.000
(c) 1.000
(d) 7.000
Answer. A

Question. The hydrogen ion concentration of a 10–8 M HCl aqueous solution at 298 K (Kw = 10^–14) is
(a) 1.0 × 10^–8 M
(b) 1.0 × 10^–6 M
(c) 1.0525 × 10^–7 M
(d) 9.525 × 10^–8 M 
Answer. C

Question. At 25°C, the dissociation constant of a base, BOH, is 1.0 × 10^–12. The concentration of hydroxyl ions in 0.01 M aqueous solution of the base would be
(a) 1.0 × 10^–5 mol L^–1
(b) 1.0 × 10^–6 mol L^–1
(c) 2.0 × 10^–6 mol L^–1
(d) 1.0 × 10^–7 mol L^–1
Answer. D

Question. Which has highest pH?
(a) CH₃COOK
(b) Na₂CO₃
(c) NH₄Cl
(d) NaNO₃ 
Answer. B

Question. Ionisation constant of CH₃COOH is 1.7 × 10^–5 and concentration of H⁺ ions is 3.4 × 10^–4. Then find out initial concentration of CH₃COOH molecules.
(a) 3.4 × 10^–4
(b) 3.4 × 10^–3
(c) 6.8 × 10^–4
(d) 6.8 × 10^–3
Answer.  D

Question. Which statement is wrong about pH and H⁺?
(a) pH of neutral water is not zero.
(b) Adding 1 N solution of CH₃COOH and 1 N solution of NaOH, pH will be seven.
(c) [H+] of dilute and hot H₂SO₄ is more than concentrated and cold H₂SO₄.
(d) Mixing solution of CH₃COOH and HCl, pH will be less than 7. 
Answer. B

Question. The concentration of [H⁺] and concentration of [OH^–] of a 0.1 aqueous solution of 2% ionised weak acid is [ionic product of water = 1 × 10^–14]
(a) 2 × 10^–3 M and 5 × 10^–12 M
(b) 1 × 10^–3 M and 3 × 10^–11 M
(c) 0.02 × 10^–3 M and 5 × 10^–11 M
(d) 3 × 10^–2 M and 4 × 10^–13 M 
Answer. A

Question. The hydride ion H– is stronger base than its hydroxide ion OH–. Which of the following reaction will occur if sodium hydride (NaH) is dissolved in water?
(a) H^– + H₂O → no reaction
(b) H^–_(aq) + H₂O → H₂O
(c) H^–_(aq) + H₂O_(l) → OH– + H₂
(d) None of these. 
Answer. C

Question. The ionic product of water at 25°C is 10^–14. Its ionic product at 90°C will be,
(a) 1 × 10^–14
(b) 1 × 10^–16
(c) 1 × 10^–20
(d) 1 × 10^–12
Answer. D

Question. If a is dissociation constant, then the total number of moles for the reaction, 2HI → H₂ + I₂ will be
(a) 1
(b) 1 – a
(c) 2
(d) 2 – a 
Answer. C

Question. The pH value of N/10 NaOH solution is
(a) 12
(b) 13
(c) 10
(d) 11 
Answer. B

Question. The pH value of a 10 M solution of HCl is
(a) equal to 1
(b) equal to 2
(c) less than 0
(d) equal to 0 
Answer. C

Question. At 80°C, distilled water has [H₃O⁺] concentration equal to 1 × 10^–6 mole/litre. The value of Kw at this temperature will be
(a) 1 × 10^–12
(b) 1 × 10^–15
(c) 1 × 10^–6
(d) 1 × 10^–9 
Answer. A

Question. 0.1 M solution of which one of these substances will act basic?
(a) Sodium borate
(b) Ammonium chloride
(c) Calcium nitrate
(d) Sodium sulphate
Answer. A

Question. The compound whose water solution has the highest pH is
(a) NaCl
(b) NaHCO₃
(c) Na₂CO₃
(d) NH₄Cl 
Answer. C

Question. Which will make basic buffer?
(a) 100 mL of 0.1 M HCl + 100 mL of 0.1 M NaOH
(b) 50 mL of 0.1 M NaOH + 25 mL of 0.1 M CH₃COOH
(c) 100 mL of 0.1 M CH₃COOH + 100 mL of 0.1 M NaOH
(d) 100 mL of 0.1 M HCl + 200 mL of 0.1 M NH4OH
Answer. D

Question. Which one of the following pairs of solutions is not an acidic buffer?
(a) CH₃COOH and CH₃COONa
(b) H₂CO₃ and Na₂CO₃
(c) H₃PO₄ and Na3PO₄
(d) HClO₄ and NaClO₄ 
Answer. D

Question. The dissociation constant of a weak acid is 1 × 10^–4.In order to prepare a buffer solution with a pH = 5, the [Salt]/[Acid] ratio should be
(a) 4 : 5
(b) 10 : 1
(c) 5 : 4
(d) 1 : 10
Answer. B

Question. Buffer solutions have constant acidity and alkalinity because
(a) these give unionised acid or base on reaction with added acid or alkali
(b) acids and alkalies in these solutions are shielded from attack by other ions
(c) they have large excess of H⁺ or OH^– ions
(d) they have fixed value of pH. 
Answer. A

Question. A buffer solution is prepared in which the concentration of NH₃ is 0.30 M and the concentration of NH₄⁺ is 0.20 M. If the equilibrium constant, Kb for NH₃ equals 1.8 × 10^–5, what is the pH of this solution? (log 2.7 = 0.43)
(a) 9.08
(b) 9.43
(c) 11.72
(d) 8.73
Answer. B

Question. In a buffer solution containing equal concentration of B^– and HB, the K_b for B^– is 10^–10. The pH of buffer solution is
(a) 10
(b) 7
(c) 6
(d) 4 
Answer. A

Question. Which of the following pairs constitutes a buffer?
(a) HCl and KCl
(b) HNO₂ and NaNO₂
(c) NaOH and NaCl
(d) HNO₃ and NH₄NO₃
Answer. B

Question. The pH value of blood does not appreciably change by a small addition of an acid or a base, because the blood
(a) can be easily coagulated
(b) contains iron as a part of the molecule
(c) is a body fluid
(d) contains serum protein which acts as buffer.
Answer. D

Question. MY and NY₃, two nearly insoluble salts, have the same Ksp values of 6.2 × 10^–13 at room temperature.
Which statement would be true in regard to MY and NY₃?
(a) The salts MY and NY₃ are more soluble in 0.5 M KY than in pure water.
(b) The addition of the salt of KY to solution of MY and NY₃ will have no effect on their solubilities.
(c) The molar solubilities of MY and NY₃ in water are identical.
(d) The molar solubility of MY in water is less than that of NY₃.
Answer. D

Question. H₂S gas when passed through a solution of cations containing HCl precipitates the cations of second group of qualitative analysis but not those belonging to the fourth group. It is because
(a) presence of HCl decreases the sulphide ion concentration
(b) solubility product of group II sulphides is more than that of group IV sulphides
(c) presence of HCl increases the sulphide ion concentration
(d) sulphides of group IV cations are unstable in HCl.
Answer. A

ONE MARK QUESTIONS

1 What happens to the concentration of products when the pressure is increased in the following reaction at equilibrium? 2NO_2(g)⇌ N₂O_4(g)?

2 Name an acid buffer and an alkaline buffer each.

3 Copper is precipitated as sulphide in the II group while Zn is precipitated as sulphide in the IV group. Explain.

4. Write the formula for the conjugate acid of (i) F^- (ii) OH^-

5. Write the formula for the conjugate base of ( i) HNO₂ , (ii) OH^-

TWO MARKS QUESTIONS

1. Give reason:

a) Equilibrium can be established only in closed system.

b) Chemical equilibrium is dynamic in nature.

2. An equilibrium mixture contains [PCl₅] = 0.15 ; [PCl₃] = 0.29 ; [Cl₂] = 0.32. If Kc for the dissociation of PCl₅ at the same temperature is 3.5, in which direction is the reaction proceeding?

3. Differentiate between

a) hydrolysis and hydration

b) solubility and solubility product

4. Calculate the solubility of BaSO₄ if its Ksp value is 1.1 x 10^-10

5. State (i) Henry’s law (ii) LeChatelier’s principle

6. Classify the following as Lewis acid or Lewis base H₂O , BF₃ , Al³⁺ , Cl^-

THREE MARKS QUESTIONS

1. The value of Kc = 6.2 at 750K for the reaction CO(g) + H₂O(g) ⇌CO2(g) + H₂(g). If initially the quantities of CO and H₂O are 2 moles in a 1 liter vessel, What would be the equilibrium concentrations of all the chemicals?

2. (i) The Kc value for the reaction SO₂ (g) + ½ O₂ (g) ⇌ SO₃ (g) is 72.5. What is the value of Kc for 2SO₃(g) ⇌ 2SO₂(g) + O₂(g)?
(ii) If the Kp value for the reaction CO₂(g) + C(s) ⇌ 2CO(g) at 1000K is 3, find value of Kc.

3. Calculate the degree of dissociation, pH, and concentration of all species at equilibrium of a 0.05M HCN solution if Ka = 4.9 x 10^-10.

4. (i) If Ka for the weak acid niacin is 1.5 x 10^-5, what is Kb for its conjugate base?
(ii) The pH of an acetic acid solution is 5.6. What is the concentration of the solution if Ka = 1.8 x 10^-7?

5. 10ml of 0.1M CaCl₂ is mixed with 15ml of 0.11M NaF. Predict whether CaF₂ will precipitate if the Ksp of CaF₂ is 5.3 x 10^-9
.
6. Which of the following is more soluble?
a) AgClor AgBr[ Ksp of AgCl = 1.8 x 10^-10 ; AgBr = 5 x 10^-13]
b) AgCNor Ni(OH)₂ [ KspAgCN = 2 x 10^-15; Ni(OH)₂ = 6 x 10^-17]

7. A buffer solution contains 0.4mol of ammonium hydroxide and 0.5mol of ammonium chloride to make a buffer solution of 1L.Calculate the pH of the resulting buffer solution. Dissociation constant of ammonium hydroxide at 25oC is 1.81x 10-5

VALUE BASED QUESTION ( FOUR MARKS)

1. In group III, the cationsFe, and Al are precipitated as hydroxides by the addition of NH₄OH to the aqueous solution of the mixture. But a small amount of NH₄Cl is added before the addition of NH₄OH. Arvinderwas confused to see why common NH⁴⁺ ion is added. He asked his friend Palvinder the purpose of adding common NH⁴⁺ ion. Palvinder explained the purpose of adding NH₄Cl and then Arvinder got satisfied.
(i) What would be the answer of Palvinder.
(ii) Why magnesium is not precipitated from a solution of it’s salt in group III.
(iii) What is basic principle behind the systematic analysis of cations and group separation? Explain.
(iv) What values are shown by Palvinder?