Acids and bases (1)

For each question choose the answer you consider to be the best.

1. Which is a Brønsted - Lowry conjugate acid/ base pair?

A. H₃O⁺ / OH^–

B. OH^– / O^2–

C. H₂SO₄ / SO₄^2–

D. NH₄⁺ / NH₂^–

2. Which species act as Brønsted - Lowry acids in the following reactions?

NH₂^–(aq) + H₂O(l) ⇌ NH₃(aq) + OH^–(aq)

CH₃NH₂(aq) + H₂O(l) ⇌ CH₃NH₃⁺ (aq) + OH^–(aq)

I. NH₃(aq)

II. CH₃NH₃⁺ (aq)

III. H₂O(l)

A. I and II only

B. I and III only

C. II and III only

D. I, II and III

3. Which equations represent acid-base reactions according to Lewis theory?

I. Fe²⁺ + 6H₂O → [Fe(H₂O)₆]²⁺

II. BF₃ + F^– → BF₄^–

III. 2H₂ + O₂ → 2H₂O

A. I and II only

B. I and III only

C. II and III only

D. I, II and III

4. Which gives an acidic solution when dissolved in water?

A. CH₃COOH

B. CH₃CHO

C. CH₃CH₂OH

D. CH₃COCH₃

5. Which substance reacts with dilute nitric acid to produce hydrogen gas?

A. FeCO₃

B. Fe(OH)₃

C. Fe₂O₃

D. Fe

6. Which substance is not a base?

A. CuO

B. NaCl

C. NaHCO₃

D. CuCO₃

7. Which list contains only strong acids?

A. HCl, HNO₃, H₂CO₃

B. HCl, HNO₃, H₂SO₄

C. CH₃COOH, H₂CO₃, H₂SO₄

D. H₂SO₄, HNO₃, CH₃COOH

8. Which can be used to distinguish between a solution of a strong monoprotic acid and a solution of weak monoprotic acid with the same concentration?

I. Add zinc to each solution and measure the rate of formation of gas produced.

II. Add sodium hydroxide solution to each solution and measure the temperature change.

III. Measure the pH

A. I and II only

B. I and III only

C. II and III only

D. I, II and III

9. Which will change the pH of a solution from value of 2 to a value of 4?

A. Doubling the concentration of H⁺(aq).

B. Doubling the concentration of OH^-(aq).

C. Decreasing the concentration of H⁺(aq) by a factor of 100.

D. Decreasing the concentration of OH^–(aq) by a factor of 100.

10. Which of the following 0.010 mol dm^-3 solutions will have the lowest pH?

A. iodoethanoic acid K_a = 6.60 x 10^-4

B. methanoic acid K_a = 1.78 x 10^-4

C. chloroethanoic acid K_a = 1.34 x 10^-3

D. 2,4-dinitrophenol K_a = 8.5 x 10^-5

11. Which is correct concerning the pH and pOH values of an aqueous solution at 298 K?

A. pH + pOH = 1 x 10¹⁴

B. pH + pOH = 1 x 10^-14

C. pH + pOH = 14

D. pH x pOH = 14

12. What will happen to the value of the pH of 1 cm³ of a solution of a strong base when 999 cm³ of water are added to it?

A. It will decrease by 3

B. It will increase by 3

C. It will decrease by a factor of 3

D. It will increase by a factor of 3

13. Which is the correct order of decreasing acid strength for the following?

2-methylpropanoic acid K_a = 1.45 x 10^-5
2,2-dimethylpropanoic acid K_a = 9.33 x 10^-6
benzoic acid K_a = 6.31 x 10^-5

A. 2,2-dimethylpropanoic acid, benzoic acid, 2-methylpropanoic acid

B. 2,2-dimethylpropanoic acid, , 2-methylpropanoic acid, benzoic acid

C. 2-methylpropanoic acid, benzoic acid, 2,2-dimethylpropanoic acid

D. benzoic acid, 2-methylpropanoic acid, 2,2-dimethylpropanoic acid

14. What happens to water ( K_w = 1 x 10^-14) when the temperature is raised from 298 K to 308 K?

H₂O(l) ⇌ H⁺(aq) + OH^–(aq) ∆H = + 57.6 kJ mol^-1

A. [H+] increases and the water stays neutral.

B. [H+] increases and the water becomes acidic.

C. [H+] decreases and the water stays neutral.

D. [H+] decreases and the water becomes basic.

15. What is the K_b expression for the reaction of methylamine with water?

16. Which could be used to make a buffer solution?

I. KOH(aq) + CH₃COOH(aq)

II. NaCH₃COO(aq) + CH₃COOH(aq)

III. NH₃(aq) + NH₄Cl(aq)

A. I and II only

B. I and III only

C. II and III only

D. I, II and III

17. What is the hydroxide ion concentration in a buffer solution in which [NH₃] = 2.00 mol dm^-3 and [NH₄⁺] = 1.00 mol dm^-3? (K_b for NH₃ = 1.8 x 10^-5)

A. 1.8 x 10^-5

B. 3.6 x 10^-5

C. 9.0 x 10^-4

D. 9.0 x 10^-6

18. Which salts dissolves in water to produce a solution with a pH value lower than 7?

I. FeCl₃(s)

II. NH₄Cl(s)

III. KCN(s)

A. I and II only

B. I and III only

C. II and III only

D. I, II and III

19. Which titration should use phenolphthalein (pK_a = 9.50) as an indicator and not methyl orange (pK_a = 3.46)?

A. NaOH(aq) + HCl(aq)

B. CH₃COOH(aq) + NH₃(aq)

C. HCl(aq) + NH₃(aq)

D. NaOH(aq) + CH₃COOH(aq)

20. At approximately what pH will an acid base indicator with a pK_a value of 5.0 change colour?

A. 3

B. 5

C. 7

D. 9

Answers

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