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IB DP Chemistry Questions

8.4 Strong and Weak Acids and Bases

Question 1

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.

Question 2

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.

Question 3

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.

Question 4

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.

Question 5

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

Question 6

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]

Question 7

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]

Question 8

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]

Question 9

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]

Question 10

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]

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