Topic 18.2: Calculations involving acids and bases

Question 1

Definition of Ka

Answer 1

Equilibrium constant for a weak acid reacting with H2O

Question 2

Interpretation of the value of Ka

Answer 2

The higher the value of Ka, the stronger the acid.

Question 3

How can the partial dissociation of a weak acid HA in water be written?

Answer 3

HA + H2O ⇌ H+ + A-

Question 4

Equilibrium expression of the partial dissociation of a weak acid HA in water

Answer 4

Ka = [H+][A-] / [HA]

Question 5

Definition of Kb

Answer 5

Equilibrium constant for a weak base reacting with H2O

Question 6

Interpretation of the value of Kb

Answer 6

The higher the value of Kb, the stronger the base.

Question 7

How can the partial dissociation of a weak base A- in water be written?

Answer 7

A- + H2O ⇌ OH- + HA

Question 8

Equilibrium expression of the partial dissociation of a weak base A- in water

Answer 8

Kb = [OH-][HA] / [A-]

Question 9

Relationship of Ka and Kb for a conjugate acid-base pair

Answer 9

(Ka)(Kb) = (H+)(OH-) = Kw

Question 10

Relationship of pKa and pKb for a conjugate acid-base pair

Answer 10

pKa + pKb = pKw = 14 (at 298 K)