Acid-Base Worksheet

(Source: )

Answers are given at the end of all worksheets. Solve the problems before looking at the

answers.

1. What is pH of 0.0054 M HCl?

2. What is pH of 0.0054 M NaOH?

3. The concentration of calcium hydroxide in a saturated solution is 0.025 M. What is the pH

of the solution? Is it acidic or basic?

4. The concentration of OH− ions in a sample of seawater is 5.0 x 10−6 M.

a. Calculate the concentration of H3O+ ions and classify the solution as neutral, acidic, or basic.

b. Calculate the pOH of the above solution, and indicate whether a small or large pOH value

is indicative of a basic solution.

5. Write the formula for each of the following:

  1. the conjugate base of NH4+ ______
  1. the conjugate base of H3PO4 ______
  1. the conjugate acid of CO32−______
  1. the conjugate acid of H2O ______
  1. the conjugate base of HSO4−______
  1. the conjugate base of H2PO4−______
  1. the conjugate base of HC6H3O52−______
  1. the conjugate acid of C2H6NH ______

6. The Ka of HNO2 is 7.1 x 10−4. Identify its conjugate base and determine the Kb of that base.

7. The following is a list of weak acids and their Ka values:

HOClhypochlorous acid 3.5 x 10−8

H2S hydrogen sulfide 1.1 x 10−7

HCN hydrocyanic acid 4.0 x 10−10

HNO2 nitrous acid 4.5 x 10−4

a. Which acid given above is the strongest? Explain your choice.

b. Write the Ka expression for the strongest acid.

c. Which acid has the strongest conjugate base? Explain your choice.

8. Complete the following:

I. In each of the following reactions, identify the conjugate acid-base pairs.

II. Using Ka or Kb values from the textbook, if you mix equal concentrations of reactants and products, determine which of the following reactions would proceed to the right or to the left as written. Briefly explain your choice in each case.

a. HF (aq) + NO3−(aq)⇌ HNO3 (aq) + F− (aq)

b. NH4+(aq) + CO32−(aq)⇌ HCO3−(aq) + NH3 (aq)

c. HCO3−(aq) + H2S (aq)⇌ H2CO3 (aq) + HS−(aq)

9. Decide which of each of the following would give an acidic, basic or neutral solution when

added to water. Explain your reasoning.

a. NaNO3

b. K3PO4

10. What is pH of 0.054 M acetic acid (HC2H3O2), Ka = 1.8 x 10−5?

11. A 0.025 M solution of a weak acid (HA) has a pH of 3.14. What is the Ka of the acid?

12. Dimethylamine, (CH3)2NH, a key intermediate in detergent manufacture, has a Kb of 5.9 x 10−4. What is the pH of 1.5 M (CH3)2NH?

Answers (Answers may vary slightly from yours b/c a different acid/base strength table was used, therefore Ka values may vary slightly.)

1. 2.27

2. 11.73

3. 12.70 Basic

4. a. [H3O+] = 2.0 x 10−9 M; this solution is basic

b. pOH = 5.30; A small pOH is indicative of a basic solution

5. a. NH3

b. H2PO4−

c. HCO3−

e. H3O+

f. SO42−

g. HPO42−

h. C6H3O53−

i. C2H6NH2+

6. The conjugate base is NO2−

Kb = 1.4 x 10−11

7. a. Nitrous acid, HNO2, is strongest because it has the highest Ka

b. Ka = [H3O+][NO2−] [HNO2]

c. Hydrocyanic acid, HCN, has the strongest conjugate base because it is the weakest acid

(lowestKa).

8. a. HF (aq) + NO3−(aq) ⇌ HNO3(aq) + F−(aq)

Acid, base, acid, base

6.8 x 10−4 strong

weaker acid, weaker base,, stronger acid, stronger base

conjugate acid/base pairs are HF/F− and HNO3/NO3− (acid listed first)

The reaction would proceed to the left because HNO3 is a strong acid and HF is a weak

acid. Reactions favor the weaker conjugate acid or base.

b. NH4+(aq) + CO32− (aq)⇌ HCO3− (aq) + NH3 (aq)

acid, base, acid, base

Ka = 5.7 x 10−10 (stronger acid)

Ka = 4.7 x 10−11 (weaker acid )

conjugate acid/base pairs are NH4+/NH3 and HCO3−/CO32−

The reaction would proceed towards the right because NH3 is the weaker base and HCO3− is the weaker acid.

c. HCO3− (aq) + H2S (aq)⇌ H2CO3 (aq) + HS−(aq)

base, acid, acid, base

Ka(H2S) = 9 x 10−8; Ka(H2CO3)= 4.5 x 10−7

weaker base, weaker acid, stronger acid, stronger base

conjugate acid/base pairs are H2CO32−/HCO3− and H2S/HS−

The reaction will favor the left because H2S is a weaker acid that H2CO3 (These Ka values may differ slightly from our table.)

9. a. neutral Na+ is a alkali metalcation (neutral); NO3– is the anion of a strong acid (neutral)

b. basic K+ is a alkali metalcation (neutral); PO43– is the anion of a weak acid (base)

10. pH = 3.01

Please take time to notice the difference in pH between 0.054 M HCl, NaOH (problems 1&2), and HC2H3O2

11.Ka = 2.1 x 10−5

12. pH = 12.47