Aqueous Equilibrium - Buffers & Titrations Examples of Multiple Choice Questions

1.

Which of the following combinations cannot produce a buffer solution?

(a) HNO₂ and NaNO₂

(b) HCN and NaCN

(c) HClO₄ and NaClO₄

(d) NH₃ and (NH₄)₂SO₄

(e) NH₃ and NH₄Br

2.

What is the pH of a solution composed of 0.20 M NH₃ and 0.15 M NH₄Cl?

(a) 2.15

(b) 4.62

(c) 8.26

(d) 9.38

(e) 8.89

3.

Calculate the ratio [CH₃COOH]/[NaCH₃COO] that gives a solution with pH = 5.00?

(a) 0.28

(b) 0.36

(c) 0.44

(d) 0.56

(e) 0.63

4.

Consider a solution which is 0.10 M in CH₃COOH and 0.20 M in NaCH₃COO. Which of the following statements is true?

(a) If a small amount of NaOH is added, the pH decreases very slightly.

(b) If NaOH is added, the OH^- ions react with the CH₃COO^- ions.

(c) If a small amount of HCl is added, the pH decreases very slightly.

(d) If HCl is added, the H⁺ ions react with CH₃COOH ions.

(e) If more CH₃COOH is added, the pH increases.

5.

A buffer was prepared by mixing 1.00 mole of ammonia and 1.00 mole of ammonium chloride to form an aqueous solution with a total volume of 1.00 liter. To 500 mL of this solution was added 30.0 mL of 1.00 M NaOH. What is the pH of this solution?

(a) 8.96

(b) 9.83

(c) 9.31

(d) 9.11

(e) 9.57

6.

How many grams of NaF would have to be added to 2.00 L of 0.100 M HF to yield a solution with a pH = 4.00?

(a) 300 g

(b) 36 g

(c) 0.84 g

(d) 6.9 g

(e) 60. g

7.

Calculate the pH that results when the following solutions are mixed.

(1) 35 mL of 0.20 M formic acid

(2) 55 mL of 0.10 M sodium formate

(3) 110 mL of water

(a) 3.64

(b) 3.11

(c) 4.58

(d) 3.39

(e) 4.20

8.

Consider an indicator that ionized as shown below for which its K_a = 1.0 x 10^-4

HIn	+	H2O		H3O+	+	In-
yellow						red

Which of the responses contains all the true statements and no others?

(1) The predominant color in its acid range is yellow.

(2) In the middle of the pH range of its color change a solution containing the indicator will probably be orange.

(3) At pH = 7.00, a solution containing this indicator (and no other colored species) will be red. (Hint: Write the equilibrium constant expression for the indicator.)

(4) At pH = 7.00, most of the indicator is in the un-ionized form.

(5) The pH at which the indicator changes color is pH = 4.

(a) 1, 3, 5

(b) 2, 4

(c) 3, 4, 5

(d) 1, 2, 3, 5

(e) another combination

9.

Calculate the pH of the solution resulting from the addition of 20.0 mL of 0.100 M NaOH to 30.0 mL of 0.100 M HNO₃.

(a) 1.35

(b) 1.70

(c) 1.95

(d) 2.52

(e) 2.80

10.

Which indicator (identified by a letter) could be used to titrate aqueous NH₃ with HCl solution?

Indicator	Acid Range Color	Color-Change pH	Basic Range Color
(a)	pink	1.2 - 2.8	yellow
(b)	blue	3.4 - 4.6	yellow
(c)	yellow	6.5 - 7.8	purple
(d)	colorless	8.3 - 9.9	red
(e)	none of these

11.

Consider the titrations of the pairs of aqueous acids and bases listed on the left. For which pair is the pH at the equivalence point stated incorrectly?

Acid-Base Pair	pH at Equivalence Point
(a) HCl + NH3	less than 7
(b) HNO3 + Ca(OH)2	equal to 7
(c) HClO4 + NaOH	equal to 7
(d) HClO + NaOH	less than 7
(e) CH3COOH + KOH	greater than 7

12.

What is the pH at the equivalence point in the titration of 100.0 mL of 0.20 M ammonia with 0.10 M hydrochloric acid?

(a) 4.6

(b) 5.2

(c) 7.0

(d) 5.5

(e) 4.9

13.

Calculate the pH of a solution prepared by mixing 300 mL of 0.10 M HF and 200 mL of 0.10 M KOH.

(a) 2.82

(b) 2.96

(c) 3.32

(d) 3.44

(e) 3.53

14.

What is the approximate pH of a solution prepared by mixing equal volumes of 0.05 M methylamine and 0.20 M hydrochloric acid?

(a) 2.57

(b) 1.12

(c) 1.63

(d) 10.5

(e) 9.8

15.

Which of the following salts give acidic aqueous solutions?

(1) KNO3	(2) KCH3COO	(3) NH4NO3	(4) RbI
(5) (NH4)2SO4	(6) BaCl2	(7) NaCN	(8) KNO2

(a) 2, 7, 8

(b) 3, 5

(c) 2, 4, 6

(d) 1, 4, 7, 8

(e) 1, 4, 6

16.

The following titration curve is the kind of curve expected for the titration of a ____ acid with a ____ base.

(a) strong, strong

(b) weak, strong

(c) strong, weak

(d) weak, weak

(e) none of these

17.

Consider the titration of 30.0 mL of 0.20 M nitrous acid by adding 0.0500 M aqueous ammonia to it. The pH at the equivalence point is _____. (Note: This is the titration of a weak acid with a weak base.)

(a) greater than 7

(b) equal to 7

(c) less than 7

(d) cannot be determined without more data (not including K_a and K_b)

(e) is impossible to predict

Answers:

1. (c) 2. (d) 3. (d) 4. (c) 5. (c) 6. (e) 7. (a) 8. (d) 9. (b) 10. (b) 11. (d) 12. (b) 13. (d) 14. (b) 15. (b) 16. (a) 17. (c)

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