8.4 Strong and Weak Acids and Bases

Which of the following best describes the significance of Ka in the context of acids?

A. It represents the concentration of the acid.

B. It indicates the strength of a base.

C. It is the acid dissociation constant, indicating the strength of an acid.

D. It represents the pH of the acid solution.

A weak acid has a Ka value of 1 x 10^-5. What can be inferred about its strength?

A. It is a very strong acid.

B. It is a moderately strong acid.

C. It is a weak acid.

D. It is a very weak acid.

Which of the following is true about the mechanism of buffer action?

A. Buffers resist changes in pH by neutralising added acid or base.

B. Buffers increase the pH of a solution.

C. Buffers decrease the pH of a solution.

D. Buffers have no effect on pH.

Which of the following is NOT a characteristic of a strong acid?

A. It completely ionises in water.

B. It has a high pH value.

C. It has a high value of Ka.

D. It donates protons readily.

What is the relationship between Ka and Kb for a conjugate acid-base pair?

A. Ka x Kb = Kw

B. Ka + Kb = Kw

C. Ka - Kb = Kw

D. Ka / Kb = Kw

a) Define Ka and explain its significance in determining the strength of an acid. [3]

b) A weak acid, HA, has a Ka value of 1.8 x 10^-5. Calculate the degree of ionisation if the concentration of HA is 0.1 M. [2]

a) Define Kb and explain how it is used to determine the strength of a base. [3]

b) Given that the pKa of a weak acid is 4.5, calculate the pKb of its conjugate base. [2]

a) Describe the mechanism of buffer action in maintaining the pH of a solution. [3]

b) Why is it important to choose a weak acid or base and its salt when preparing a buffer solution? [2]

a) Explain the difference between a strong acid and a weak acid in terms of their ionisation in water. [3]

b) If a strong acid has a pH of 2, what would be the concentration of [H+] ions in the solution? [2]

c) How does the pH of a weak acid compare to its pKa value? [2]

a) Describe the significance of pKa in the context of acid-base equilibria. [3]

b) If a weak base, BOH, has a pKb of 5.2, calculate its Kb value. [2]

c) How would the addition of its conjugate acid, BH+, affect the pH of the BOH solution? [3]