Practice Problems Acids & Bases

1. Write equations to represent the ionization of HI as an acid in both the Arrhenius and Brønsted-Lowry theories.

2. Write equations for the ionizations and K_a expressions for each of the following Brønsted-Lowry weak acids.

(a) HOClO

(b) CH₃CH₂COOH

(c) HCN

(d) C₆H₅OH

3. Explain how the strengths of

(a) binary acids are affected by bond energies and the ionic radii of the anions they produce

(b) oxoacids are affected by the electronegativity of the central nonmetal atom and the number of terminal O atoms

4. For each of the following, identify the conjugate acid-base pairs.

(a) HOClO₂(aq) + H₂O(l) → ← H₃O⁺(aq) + OClO₂^–(aq)

(b) HSeO₄^–(aq) + NH₃(aq) → ← NH₄⁺(aq) + SeO₄^2–(aq)

(c) HCO₃^–(aq) + OH^–(aq) → ← CO₃^2–(aq) + H₂O(l)

(d) C₅H₅NH⁺(aq) + H₂O(l) → ← C₅H₅N(aq) + H₃O⁺(aq)

5. Phenol, C₆H₅OH, used as a disinfectant and in the manufacture of plastics, dyes, and indicators, ionizes as an acid.

C₆H₅OH(aq) + H₂O(l) → ← H₃O⁺(aq) + C₆H₅O^–(aq)

K_a = 1.0×10^–10

Arrange the following substituted phenols in the order in which you would expect their K_a values to increase. Where would you expect phenol itself to fit into this ranking?

(a) 3-chlorophenol

(b) 2,4-dichlorophenol

(c) 2,4,6-trichlorophenol

(d) 4-chlorophenol

6. What is the pH of each of the following aqueous solutions?

(a) 0.039 M HCl

(b) 0.070 M KOH

(c) 0.65 M HBr

(d) 2.5×10^–4 M Ca(OH)₂

7. What is the pOH of each of the following aqueous solutions?

(a) 0.073 M LiOH

(b) 1.75 M NaOH

(c) 0.045 M Ba(OH)₂

(d) 9.1×10^–2 M HClO₄

8. Describe how you would prepare 2.00 L of an aqueous solution having pH = 3.60, if you had a supply of 0.100 M HCl available.

9. Which has the lower pH, 0.00048 M H₂SO₄ or a vinegar solution having pH = 2.42?

10. Hydrazoic acid, HN₃ (pK_a = 4.72), is perhaps best known through its sodium salt, sodium azide, NaN₃, the gas forming substance in automobile air-bag systems. What molarity of HN₃ is required to produce an aqueous solution with pH = 3.10?

11. A 1.00 g sample of aspirin (acetylsalicylic acid) is dissolved in 0.300 L of water at 25 °C, and its pH is found to be 2.62. What is the K_a of aspirin?

o–C₆H₄(OCOCH₃)COOH(aq) + H₂O(l) → ← H₃O⁺(aq) + o–C₆H₄(OCOCH₃)COO^–(aq)

K_a = ?

12. Codeine, C₁₈H₂₁NO₃, a commonly prescribed painkiller, is a weak base. A saturated aqueous solution contains 1.00 g codeine in 120 mL of solution and has a pH = 9.8. What is the K_b of codeine?

C₁₈H₂₁NO₃(aq) + H₂O(l) → ← [C₁₈H₂₁NHO₃]⁺(aq) + OH^–;(aq)

K_b = ?

13. Calculate the pH of 0.105 M CCl₃COOH (trichloroacetic acid, pK_a = 0.52)

14. Piperidine, C₅H₁₁N (pK_b = 2.89), is a colorless liquid having the odor of pepper. Calculate the pH of 0.00250 M C₅H₁₁N.

15. For a solution that is 0.15 M H₃PO₄(aq), determine (a) pH, (b) [H₃PO₄], (c) [H₂PO₄^–], (d) [HPO₄^2–], and (e) [PO₄^3–].

16. Predict whether each of the following solutions is acidic, basic, or neutral. Write balanced equation(s) for any hydrolysis reaction(s) that occur.

(a) RbClO₄(aq)

(b) CH₃CH₂NH₃Br(aq)

(c) HCOONH₄(aq)

17. Predict whether each of the following solutions is acidic, basic, or neutral. Write balanced equation(s) for any hydrolysis reaction(s) that occur.

(a) CH₃CH₂COOK(aq)

(b) Mg(NO₃)₂(aq)

(c) NH₄CN(aq)

18. Which of the following 0.100 M solutions has the lowest pH: (a) NaNO₃, (b) CH₃COOK, (c) NH₄I, or (d) Na₃PO₄?

19. For a solution that is 0.080 M NaOCl, (a) write an equation for the hydrolysis that occurs, and determine (b) the equilibrium constant for this hydrolysis and (c) the pH.

20. Calculate [NH₄⁺] in a solution that is 0.15 M NH₃ and 0.015 M KOH.

21. Predict whether an aqueous solution can be made up to have the following concentrations or whether a chemical reaction must occur.

(a) 0.25 M CH₃COONa and 0.15 M HI

(b) 0.050 M KNO₂ and 0.18 M KNO₃

(c) 0.0050 M Ca(OH)₂ and 0.0010 M HNO₃

(d) 0.20 M NH₄Cl and 0.35 M NaOH

22. A solution is 0.405 M HCOOH (formic acid) and 0.326 M in the salt HCOONa (sodium formate). What is the pH of the buffer solution?

23. Identify the Lewis acid and Lewis base in each of the following reactions.

(a) OH^–(aq) + Al(OH)₃(s) → Al(OH)₄^–(aq)

(b) Cu²⁺(aq) + 4 NH₃(aq) → [Cu(NH₃)₄]²⁺(aq)

(c) CO₂(g) + OH^–(aq) → HCO₃^–(aq)

24. Can a solution have [H₃O⁺] = 2×[OH^–]? Can a solution have pH = 2×pOH? If so, will the two solutions be the same?

25. Calculate the pH of a solution that is 1.0×10^–8 M HCl.

26. Normal rainfall is made slightly acidic from the dissolving of atmospheric CO₂ in the rainwater and ionization of the resulting carbonic acid, H₂CO₃. At a CO₂(g) partial pressure of 1 atm and a temperature of 25 °C, the solubility of CO₂(g) in water is 0.759 mL CO₂ at STP per mL H₂O. Given that air contains 0.036% CO₂ by volume, estimate the pH of rainwater that is saturated with CO₂(g). (Hint: Recall Henry's law, and assume that the dissolved CO₂ is present as carbonic acid.)

Answers