acids and bases questions

1. Which statement explains why ammonia can act as a Lewis base?

A. Ammonia can donate a lone pair of electrons.

B. Ammonia can accept a lone pair of electrons.

C. Ammonia can donate a proton.

D. Ammonia can accept a proton.(Total 1 mark)

2. Consider the equilibrium below.

CH3CH

2COOH(aq) + H

2O(l) CH

3CH

2COO–(aq) + H

3O+(aq)

Which species represent a conjugate acid-base pair?

A. CH3CH

2COOH and H

2O

B. H2O and CH

3CH

2COO–

C. H3O+ and H

2O

D. CH3CH

2COO– and H

3O+

(Total 1 mark)

3. Which salts will produce an acidic solution when dissolved in water?

I. CH3COOK

II. NH4NO

3

III. Al2(SO

4)3

A. I and II only

B. I and III only

C. II and III only

D. I, II and III(Total 1 mark)

IB Questionbank Chemistry 1

4. The Kb value for a base is 5.0 × 10–2 mol dm–3 at 298 K. What is the K

a value for its conjugate

acid at this temperature?

A. 5.0 × 10–2

B. 2.0 × 10–6

C. 2.0 × 10–12

D. 2.0 × 10–13

(Total 1 mark)

CH3CH

2COO–(aq) + H

3O+(aq)

Which species represent a conjugate acid-base pair?

A. CH3CH

2COOH and H

2O

B. H2O and CH

3CH

2COO–

C. H3O+ and H

2O

D. CH3CH

2COO– and H

3O+

(Total 1 mark)

5. Which compounds can be mixed together as solutions of equal volume and concentration to form a buffer solution?

A. Nitric acid and potassium hydroxide

B. Nitric acid and potassium nitrate

C. Propanoic acid and potassium hydroxide

D. Propanoic acid and potassium propanoate(Total 1 mark)


6. Which is not a conjugate acid-base pair?

A. HNO3 and NO

3–

B. CH3COOH and CH

3COO–

C. H3O+ and OH–

D. HSO4– and SO

42–

(Total 1 mark)

7. Which 0.10 mol dm–3 solution would have the highest conductivity?

A. HCl

B. NH3

C. CH3COOH

D. H2CO

3

(Total 1 mark)

8. The pH of a solution changes from pH = 2 to pH = 5. What happens to the concentration of the hydrogen ions during this pH change?

A. It decreases by a factor of 1000

B. It increases by a factor of 1000

C. It decreases by a factor of 100

D. It increases by a factor of 100(Total 1 mark)


9. Based on information in the table below, which acid is the strongest?

Acid pKa

Ka

A. HA 2.0 –

B. HB – 1 × 10–3

C. HC 4.0 –

D. HD – 1 × 10–5

(Total 1 mark)

10. Which combination will form a buffer solution?

A. 100 cm3 of 0.10 mol dm–3 hydrochloric acid with 50 cm3 of 0.10 mol dm–3 sodium hydroxide.

B. 100 cm3 of 0.10 mol dm–3 ethanoic acid with 50 cm3 of 0.10 mol dm–3 sodium hydroxide.

C. 50 cm3 of 0.10 mol dm–3 hydrochloric acid with 100 cm3 of 0.10 mol dm–3 sodium hydroxide.

D. 50 cm3 of 0.10 mol dm–3 ethanoic acid with 100 cm3 of 0.10 mol dm–3 sodium hydroxide.(Total 1 mark)


11. The graph below shows the titration curve of 25 cm3 of 0.100 mol dm–3 of hydrochloric acid with sodium hydroxide, of 0.100 mol dm–3 concentration. The indicator methyl orange was used to determine the equivalence point. Methyl orange has a pH range of 3.2–4.4.

If the hydrochloric acid was replaced by ethanoic acid of the same volume and concentration, which property of the titration would remain the same?

A. The initial pH

B. The pH at the equivalence point

C. The volume of strong base, NaOH, needed to reach the equivalence point

D. The colour of the titration mixture just before the equivalence point is reached(Total 1 mark)

12. Which property is characteristic of acids in aqueous solution?

A. Acids react with ammonia solution to produce hydrogen gas and a salt.

B. Acids react with metal oxides to produce oxygen gas, a salt and water.

C. Acids react with reactive metals to produce hydrogen gas and a salt.

D. Acids react with metal carbonates to produce hydrogen gas, a salt and water.(Total 1 mark)


13. A student has equal volumes of 1.0 mol dm–3 sodium hydroxide and ammonia solutions.Which statement about the solutions is correct?

A. Sodium hydroxide has a lower electrical conductivity than ammonia.

B. Sodium hydroxide has a higher hydrogen ion concentration than ammonia.

C. Sodium hydroxide has a higher pH than ammonia.

D. Sodium hydroxide has a higher hydroxide ion concentration than ammonia.(Total 1 mark)

14. Which statement about acids is correct?

A. A Brønsted-Lowry acid donates an electron pair.

B. A Lewis acid donates a proton.

C. A Brønsted-Lowry acid accepts a proton.

D. A Lewis acid accepts an electron pair.(Total 1 mark)

15. What is the Kb expression for the reaction of ethylamine with water?

A. Kb = [CH

3CH

2NH

3+][OH–]

B. Kb = ]NHCH[CH

]][OHNHCH[CH

223

323−+

C. Kb = ]NHCH[CH

O]][HNHCH[CH

223

2323+

D. Kb = [CH

3CH

2NH

2][H

2O]

(Total 1 mark)


16. When these 1.0 mol dm–3 acidic solutions are arranged in order of increasing strength (weakest first), what is the correct order?

acid in solution X Ka = 1.74 × 10–5 mol dm–3 at 298 K

acid in solution Y Ka = 1.38 × 10–3 mol dm–3 at 298 K

acid in solution Z Ka = 1.78 × 10–5 mol dm–3 at 298 K

A. X < Z < Y

B. X < Y < Z

C. Z < X < Y

D. Y < X < Z(Total 1 mark)

17. Consider an acid-base indicator solution.

HIn(aq) H+(aq) + In–(aq)colour A colour B

What is the effect on this acid-base indicator when sodium hydroxide solution is added to it?

A. Equilibrium shifts to the right and more of colour B is seen.

B. Equilibrium shifts to the left and more of colour B is seen.

C. Equilibrium shifts to the right and more of colour A is seen.

D. Equilibrium shifts to the left and more of colour A is seen.(Total 1 mark)


18. Which species behave as Brønsted-Lowry acids in the following reversible reaction?

H2PO

4–(aq) + CN–(aq) HCN(aq) + HPO

42–(aq)

A. HCN and CN–

B. HCN and HPO42–

C. H2PO

4– and HPO

42–

D. HCN and H2PO

4–

(Total 1 mark)

19. Which of the following are weak acids in aqueous solution?

I. CH3COOH

II. H2CO

3

III. HCl

A. I and II only

B. I and III only

C. II and III only


20. pKw

for water at 10 °C = 14.54. What is the pH of pure water at this temperature?

A. 6.73

B. 7.00

C. 7.27

D. 7.54(Total 1 mark)


21. What is Kb for the aqueous fluoride ion given that K

w is 1.0 × 10–14 and K

a for HF is 6.8 × 10–4

at 298 K?

A.4108.6

1−×

B. (6.8 × 10–4)(1.0 × 10–14)

C.4

14

108.6

100.1−

−

××

D. 6.8 × 10–4

(Total 1 mark)

22. Which of the following could be added to a solution of ethanoic acid to prepare a buffer?

A. Sodium hydroxide

B. Hydrochloric acid

C. Sodium chloride

D. More ethanoic acid(Total 1 mark)

23. What is the conjugate base of H2CO

3 according to the Brønsted-Lowry theory?

A. CO32–

B. HCO3–

C. H3CO

3+

D. CO2

(Total 1 mark)


24. A solution of acid A has a pH of 1 and a solution of acid B has a pH of 2. Which statement must be correct?

A. Acid A is stronger than acid B

B. [A] > [B]

C. The concentration of H+ ions in A is higher than in B

D. The concentration of H+ ions in B is twice the concentration of H+ ions in A(Total 1 mark)

25. Define the terms acid and base according to the Brønsted-Lowry theory and state one example of a weak acid and one example of a strong base.

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A solution of acid A has a pH of 1 and a solution of acid B has a pH of 2. Which statement must be correct?

A. Acid A is stronger than acid B

B. [A] > [B]

C. The concentration of H+ ions in A is higher than in B

D. The concentration of H+ ions in B is twice the concentration of H+ ions in A(Total 1 mark)


26. Describe two different methods, one chemical and one physical, other than measuring the pH, that could be used to distinguish between ethanoic acid and hydrochloric acid solutions of the same concentration.

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27. Black coffee has a pH of 5 and toothpaste has a pH of 8. Identify which is more acidic and deduce how many times the [H+] is greater in the more acidic product.

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28. (i) Define the terms acid and base according to the Brønsted-Lowry theory. Distinguish between a weak base and a strong base. State one example of a weak base.

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(ii) Weak acids in the environment may cause damage. Identify a weak acid in the environment and outline one of its effects.

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(Total 5 marks)


29. The graph below indicates the pH change during the titration of 20.0 cm3 of 0.100 mol dm–3 of CH

3COOH(aq) with 0.100 mol dm–3 KOH(aq). From the graph, identify the volume of

KOH(aq) and the pH at the equivalence point.

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30. Determine the pH of the solution resulting when 100 cm3 of 0.50 mol dm–3 HCl(aq) is mixed with 200 cm3 of 0.10 mol dm–3 NaOH(aq).

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31. Define an acid in terms of the Lewis theory. Deduce, giving a reason, whether NF3 is able to

function as a Lewis acid or as a Lewis base.

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32. Describe two different properties that could be used to distinguish between a 1.00 mol dm–3 solution of a strong monoprotic acid and a 1.00 mol dm–3 solution of a weak monoprotic acid.

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33. Explain, using the Brønsted-Lowry theory, how water can act either as an acid or a base. In each case identify the conjugate acid or base formed.

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34. Ammonia, NH3, is a weak base. It has a pK

b value of 4.75.

Calculate the pH of a 1.00 × 10–2 mol dm–3 aqueous solution of ammonia at 298 K.

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35. (a) (i) State an equation for the reaction of ethanoic acid with water.

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...........................................................................................................................(1)

(ii) Calculate the pH of 0.200 mol dm–3 ethanoic acid (pKa = 4.76).

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...........................................................................................................................(3)


(b) Determine the pH of a solution formed from adding 50.0 cm3 of 1.00 mol dm–3 ethanoic acid, CH

3COOH(aq), to 50.0 cm3 of 0.600 mol dm–3 sodium hydroxide, NaOH(aq).

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(c) Explain how the solution formed in part (b) can act as a buffer. Use equations to support your answer.

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(Total 10 marks)

36. Water is an important substance that is abundant on the Earth’s surface. Water dissociates according to the following equation.

H2O(l) H+(aq) + OH–(aq)

(i) State the equilibrium constant expression for the dissociation of water.(1)

(ii) Explain why even a very acidic aqueous solution still has some OH– ions present in it.(1)


(iii) State and explain the effect of increasing temperature on the equilibrium constant above given that the dissociation of water is an endothermic process.

(3)

(iv) The pH of a solution is 2. If its pH is increased to 6, deduce how the hydrogen ion concentration changes.

(2)(Total 7 marks)

37. Water is an important substance that is abundant on the Earth’s surface.

(i) State the expression for the ionic product constant of water, Kw

.

(1)

(ii) Explain why even a very acidic aqueous solution still has some OH– ions present in it.(1)

(iii) State and explain the effect of increasing temperature on the value of Kw

given that the

ionization of water is an endothermic process.(3)

(iv) State and explain the effect of increasing temperature on the pH of water.(2)

(Total 7 marks)

38. Buffer solutions resist small changes in pH. A phosphate buffer can be made by dissolving NaH

2PO

4 and Na

2HPO

4 in water, in which NaH

2PO

4 produces the acidic ion and Na

2HPO

4

produces the conjugate base ion.

(i) Deduce the acid and conjugate base ions that make up the phosphate buffer and state the ionic equation that represents the phosphate buffer.

(3)

(ii) Describe how the phosphate buffer minimizes the effect of the addition of a strong base, OH–(aq), to the buffer. Illustrate your answer with an ionic equation.

(2)


(iii) Describe how the phosphate buffer minimizes the effect of the addition of a strong acid, H+(aq), to the buffer. Illustrate your answer with an ionic equation.

(2)(Total 7 marks)

39. A 0.10 mol dm–3 ammonia solution is placed in a flask and titrated with a 0.10 mol dm–3 hydrochloric acid solution.

(i) Explain why the pH of the ammonia solution is less than 13.(2)

(ii) Estimate the pH at the equivalence point for the titration of hydrochloric acid with ammonia and explain your reasoning.

(2)

(iii) State the equation for the reaction of ammonia with water and write the Kb expression for

NH3(aq).

(2)

(iv) When half the ammonia has been neutralized (the half-equivalence point), the pH of the solution is 9.25. Deduce the relationship between [NH

3] and [NH

4+] at the half-

equivalence point.(1)

(v) Determine pKb and K

b for ammonia based on the pH at the half-equivalence point.

(3)

(vi) Describe the significance of the half-equivalence point in terms of its effectiveness as a buffer.

(1)(Total 11 marks)


40. (i) Define a Brønsted-Lowry acid.(1)

(ii) Deduce the two acids and their conjugate bases in the following reaction:

H2O(l) + NH

3(aq) OH–(aq) + NH

4+(aq)

(2)

(iii) Explain why the following reaction can also be described as an acid-base reaction.

F–(g) + BF3(g) BF

4–(s)

(2)(Total 5 marks)

41. Ethanoic acid, CH3COOH, is a weak acid.

(i) Define the term weak acid and state the equation for the reaction of ethanoic acid with water.

(2)

(ii) Vinegar, which contains ethanoic acid, can be used to clean deposits of calcium carbonate from the elements of electric kettles. State the equation for the reaction of ethanoic acid with calcium carbonate.

(2)(Total 4 marks)

42. Some of the most important processes in chemistry involve acid-base reactions.

(i) Calculate the Ka value of benzoic acid, C

6H

5COOH, using Table 15 in the Data Booklet.

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......................................................................................................................................(1)


(ii) Based on its Ka value, state and explain whether benzoic acid is a strong or weak acid.

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......................................................................................................................................(2)

(iii) Determine the hydrogen ion concentration and the pH of a 0.010 mol dm–3 benzoic acid solution. State one assumption made in your calculation.

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(Total 7 marks)

43. The equations of two acid-base reactions are given below.

Reaction A NH3(aq) + H

2O(l)

aq)(NH 4+

+ OH–(aq)

The reaction mixture in A consists mainly of reactants because the equilibrium lies to the left.

Reaction B NH2–(aq) + H

2O(l)

aq)(NH 3 + OH–(aq)

The reaction mixture in B consists mainly of products because the equilibrium lies to the right.


(i) For each of the reactions A and B, deduce whether water is acting as an acid or a base and explain your answer.

(2)

(ii) In reaction B, identify the stronger base, NH2– or OH– and explain your answer.

(2)

(iii) In reactions A and B, identify the stronger acid, NH4+ or NH

3 (underlined) and explain

your answer.(2)

(Total 6 marks)

44. (a) Describe two different experimental methods to distinguish between aqueous solutions of a strong base and a weak base.

(5)

(b) Two acidic solutions, X and Y, of equal concentrations have pH values of 2 and 6 respectively.

(i) Calculate the hydrogen ion concentrations in the two solutions and identify the stronger acid.

(2)

(ii) Determine the ratio of the hydrogen ion concentrations in the two solutions X and Y.

(1)(Total 8 marks)


45. Which mixtures act as buffer solutions?

I. 100 cm3 0.1 mol dm–3 ethanoic acid and 100 cm3 0.1 mol dm–3 sodium ethanoate

II. 100 cm3 0.1 mol dm–3 ethanoic acid and 50 cm3 0.1 mol dm–3 sodium hydroxide

III. 100 cm3 0.1 mol dm–3 ethanoic acid and 100 cm3 0.5 mol dm–3 sodium hydroxide

A. I and II only

B. I and III only

C. II and III only



acids and bases questions

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