Acids Quiz #8 Buffers and Indicators Answers

1. Consider the following acid solutions:

I. H₂CO₃ II. HClO₄ III. HF

Which of the above acids would form a buffer solution when its conjugate base is added?

A. I only

B. II only

C. I and III only

D. I, II, and III only

2. Consider the following base indicator:

HInd ⇄ H⁺ + Ind^-

When the indicator is added to different solutions, the following data are obtained:

Solution	1.0 M HCl	1.0 M HAl	1.0 M HA2
Colour	Yellow	Blue	Yellow

The acids HA_l, HA₂, and HInd listed in the order of decreasing acid strength is

A. HA₂, HInd, HA_l

B. HInd, HA_l, HA₂

C. HA₂, HA_l, HInd

D. HA_l, HInd, HA₂

3. Which of the following compounds, when added to a solution of ammonium nitrate, will result in the formation of a buffer solution?

A. Ammonia

B. Nitric acid

C. Sodium nitrate

D. Ammonium chloride

4. Which of the following represents a buffer equilibrium?

A. HI + H₂O ⇄ H₃O⁺ + I^-

B. HCl + H₂O ⇄ H₃O + Cl^-

C. HCN + H₂O ⇄ H₃O⁺ + CN^-

D. HClO₄ + H₂O ⇄ H₃O + ClO₄^-

5. Consider the following equilibrium:

HF_(aq) + H₂O_(l) ⇄ H₃O⁺_(aq) + F^-_(aq)

The above system will behave as a buffer when the [F^-] is approximately equal to

A. K_a

B. [HF]

C. [H₂O]

D. [H₃O⁺]

6. A basic buffer solution can be prepared by mixing equal numbers of moles of

A. NH₄Cl and HCl

B. NaCl and NaOH

C. Na₂CO₃ and NaHCO₃

D. NaCH₃COO and CH₃COOH

7. Which of the following would be used to prepare an acidic buffer solution?

A. HF and H₃O⁺

B. NaHS and H₂S

C. NH₃ and NH₄Cl

D. HCl and NaCl

8. HCN_(aq) + H₂O ⇌ H₃O⁺_(aq) + CN^-_(aq)

            1.0 M 0.0001 M 0.0001 M

Why is the solution above not considered to be a true buffer solution?

A. excessive [HCN]

B. excessive [H₃O⁺]

C. insufficient [CN^-]

D. insufficient [HCN]

9. What could be added to 1.0 L of this solution in order for it to behave as a true buffer?

A. 1.0 mol HCl

B. 1.0 mol HCN

C. 1.0 mol H₃O⁺

D. 1.0 mol NaCN

10. Which of the following could typically be used to prepare a buffer solution?

A. NaHS and H₂S

B. H₂S and Na₂S

C. HNO₃ and NaNO₃

D. HNO₃ and NaNO₂

11. What happens to the pH of a buffer solution if a small amount of acid is added?

A. The pH remains constant.

B. The pH increases slightly.

C. The pH decreases slightly.

D. The pH decreases significantly.

12. Consider the following buffer equilibrium:

HF + H₂O ⇌ H₃O⁺ + F^-

What concentration would limit the buffering action if acid were added?

A. [F^-]

B. [HF]

C. [H₂O]

D. [H₃O⁺]

13. Consider the following buffer equilibrium:

HF + H₂O ⇌ H₃O⁺ + F^-

What concentration would limit the buffering action if base were added?

A. [F^-]

B. [HF]

C. [H₂O]

D. [H₃O⁺]

14. Which term does the following statement best describe? A mixture of a weak

acid and its conjugate base, each with distinguishing colours.

A. buffer

B. titration

C. indicator

D. conjugate

15. The HC₂O₄^-_(aq) ion will act as

A. a base since Ka > Kb

B. a base since Ka < Kb

C. an acid since Ka > Kb

D. an acid since Ka < Kb

16. What do a chemical indicator and a buffer solution typically both contain?

A. a strong acid and its conjugate acid

B. a strong acid and its conjugate base

C. a weak acid and its conjugate acid

D. a weak acid and its conjugate base

17. What is the approximate pH and Ka at the transition point for phenol red?

pH Ka

A. 6.0 6.3 x 10^-7

B. 7.3 3.1 x 10^-14

C. 7.3 5.0 x 10^-8

D. 8.0 1.0 x 10^-8

18. Which of the following acids could not be present in a buffer solution?

A. HF

B. HNO₂

C. H₂SO₃

D. HCl

19. The indicator phenol red will be red in which of the following solutions?

A. 1.0 M HF

B. 1.0 M HBr

C. 1.0 M NH₄Cl

D. 1.0 M NaHCO₃

20. Which of the following chemical indicators has a Ka = 1.6 x 10^-4 ?

A. methyl orange

B. phenolphthalein

C. thymolphthalein

D. bromcresol green

21. Which of the following chemical indicators has a Ka = 7.9 x 10^-10 ?

A. methyl orange

B.        phenolphthalein

C. thymolphthalein

D. bromcresol green

22. What is the Ka for phenolphthalein?

A. 1 x 10^-14

B. 8 x 10^-10

 C. 1 x 10⁹

D. 1.0 x 10^-7

23. What volume of 0.250 M KOH is required to titrate 0.00230 mol of the weak

acid H₂CO₄ ?

A. 1.15 mL

B. 4.60 mL

C. 9.20 mL

D.        18.4 mL

24. What is the net ionic equation for the titration of H₃PO_4(aq) with Sr(OH)_2(aq) ?

            A. H⁺_(aq) + OH^- _(aq) ® H₂O_(l)

B. 6H⁺_(aq) + 6OH^-_(aq) ® 6H₂O_(l)

C. 2H₃PO_4(aq) + 3Sr²⁺_(aq) + 6OH^-_(aq) ® Sr₃(PO₄)_2(s) + 6H₂O_(l)

D. 6H⁺_(aq) + 2PO₄^3-_(aq) + 3Sr²⁺_(aq) + 6OH^- _(aq) ® 3Sr²⁺ + 2PO₄^3-_(aq) + 6H₂O_(l)

25. Which of the following will have the smallest Ka value?

A. HF

B. H₂CO₃

C. H₃PO₄

D. CH₃COOH

26. Which of the following will have the smallest Kb value?

A. IO₃^-

B. NH₃

C. CN^-

D. HPO₄^2-

27. What volume of 0.500 M NaOH is required to neutralize 25.0 mL 0.250 M HBr ?

A. 5.00 mL

B. 12.5 mL

C. 20.0 mL

D. 25.0 mL

28. Which of the following equations correctly represents the reaction of a metallic

oxide with water?

A. K₂O + H₂O ® 2KOH

B. SO₃ + H₂O ® H₂SO₄

C. Na₂O + H₂O ® Na₂O₂ + H₂

D. NaOH + HCl ® NaCl + HOH

29. Which of the following equations describes the dissociation of the salt,

ammonium chloride, in water?

A. NH₄Cl_(s) ® NH₄Cl_(aq)

B. NH₄⁺_(aq) + Cl^-_(aq) ® NH₄Cl_(s)

C. NH₄Cl_(s) ® NH₄⁺_(aq) + Cl^-_(aq)

D. NH₄⁺_(aq) + H₂O_(l) ® H₃O⁺_(aq) + NH_3(aq)

30. Which of the following salt solutions is acidic?

A. NaBr

B. AlCl₃

C. Li₂CO₃

D. NaHCO₃