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IB DP Chemistry Questions

18.2 Calculations Involving Acids and Bases

Question 1

Which of the following statements is true regarding the relationship between Ka, Kb, and Kw for a conjugate acid-base pair?

A. Ka x Kb = Kw

B. Ka + Kb = Kw

C. Ka / Kb = Kw

D. Ka - Kb = Kw

Question 2

Given that the Ka for a weak acid is 1.0 x 10^-5, what is the Kb for its conjugate base if Kw = 1.0 x 10^-14?

A. 1.0 x 10^-9

B. 1.0 x 10^-5

C. 1.0 x 10^-19

D. 1.0 x 10^-10

Question 3

A strong acid is one that:

A. Has a low Ka value

B. Completely dissociates in water

C. Has a high Kb value

D. Partially dissociates in water

Question 4

Which of the following is NOT a characteristic of a weak base?

A. It has a low Kb value

B. It partially dissociates in water

C. It has a high Ka value

D. It does not release all its hydroxide ions in water

Question 5

If the Kb of ammonia (NH3) is 1.8 x 10^-5, what is the Ka of its conjugate acid (NH4+)?

A. 5.6 x 10^-10

B. 1.8 x 10^-5

C. 5.6 x 10^-20

D. 1.8 x 10^-10

Question 6

a) Define the terms Ka and Kb in the context of acid-base chemistry. [2]

b) Given that the value of Kw is 1.0 x 10^-14 at 25°C, calculate the value of Kb for an acid with a Ka of 1.8 x 10^-5. [3]

Question 7

a) Explain the relationship between the magnitude of Ka and the strength of an acid. [2]

b) A weak base B has a Kb of 2.5 x 10^-6. Predict the pH of a 0.1 M solution of this base at 25°C. [3]

Question 8

a) Describe the difference between a Lewis acid and a Brønsted-Lowry acid. [3]

b) Given a weak acid HA with a Ka of 3.2 x 10^-4, determine whether the acid is strong or weak based on its dissociation constant. [2]

Question 9

a) Describe how the strength of an acid can be predicted from its dissociation constant, Ka. [2]

b) A solution of a weak acid, HA, has a pH of 3.5. Calculate the concentration of H+ ions in the solution. [2]

c) If the concentration of HA in the solution is 0.1 M, determine its Ka value. [3]

Question 10

a) Define a Lewis base and explain how it differs from a Brønsted-Lowry base. [3]

b) Given that Kw is 1.0 x 10^-14 at 25°C, and the Ka for an acid HA is 2.0 x 10^-6, calculate the Kb for its conjugate base A-. [2]

c) Would A- be considered a strong or weak base? Justify your answer. [2]

Question 11

Which of the following acids has the strongest acidic character?

A. Ka = 1.0 x 10^-3

B. Ka = 1.0 x 10^-5

C. Ka = 1.0 x 10^-7

D. Ka = 1.0 x 10^-9

Question 12

A solution has a [OH-] concentration of 1.0 x 10^-3 mol/L. What is the [H+] concentration?

A. 1.0 x 10^-11 mol/L

B. 1.0 x 10^-3 mol/L

C. 1.0 x 10^-7 mol/L

D. 1.0 x 10^-14 mol/L

Question 13

Which of the following is true about a solution with a pH of 7?

A. It is acidic

B. It is basic

C. It is neutral

D. It has a high Ka value

Question 14

A weak acid has a Ka of 1.0 x 10^-6. 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 very weak acid

D. It is a moderately weak acid

Question 15

What is the Kb of a base if its conjugate acid has a Ka of 2.5 x 10^-4?

A. 4.0 x 10^-11

B. 2.5 x 10^-4

C. 4.0 x 10^-10

D. 2.5 x 10^-10

Question 16

a) What is the significance of the equivalence point in a titration? [3]

b) In a titration of a weak acid with a strong base, describe the pH at the equivalence point. [2]

c) Explain why the pH at the equivalence point is not necessarily 7. [3]

Question 17

a) What is the relationship between Ka, Kb, and Kw? [2]

b) If a solution of a weak base B has a Kb of 4.5 x 10^-9, predict the pH of a 0.05 M solution of this base at 25°C. [3]

c) How would the pH change if the concentration of B was doubled? [2]

Question 18

a) Describe the relationship between the dissociation constants Ka and Kb for a conjugate acid-base pair. [2]

b) A weak acid, HA, has a Ka of 1.8 x 10^-5. Calculate the Kb for its conjugate base, A-. [2]

c) If a 0.1 M solution of A- has a pH of 9.2, determine the concentration of OH- ions in the solution. [3]

d) How would the concentration of OH- ions change if the temperature of the solution was increased? Justify your answer. [3]

Question 19

a) Define the term 'buffer solution'. [2]

b) Explain how a buffer solution resists changes in pH when small amounts of acid or base are added. [3]

c) Given a buffer solution made from a weak acid, HA, and its conjugate base, A-, with equal concentrations of 0.1 M, calculate the pH of the buffer if the Ka for HA is 2.0 x 10^-6. [4]

d) How would the pH of the buffer solution change if some strong acid was added to it? [3]

Question 20

a) Differentiate between a strong acid and a weak acid based on their dissociation in water. [2]

b) If the pOH of a 0.05 M solution of a strong base is 2.3, determine the concentration of H+ ions in the solution. [3]

c) Using the above information, calculate the pH of the solution. [2]

d) Describe how the pH would change if the concentration of the strong base was halved. [3]

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