pKa Practice Problems

Rank the following original compounds in order from strongest base to weakest base.

Rank each compound in the following groups in order from weakest base to strongest base. (i) potassium benzoate, potassium ethoxide, and potassium phenoxide; and (ii) 2-methylpyridine, potassium ethoxide, and potassium acetate

Arrange the given compounds in increasing order of their basicity. Provide a suitable reason for your answer.

Estimate the pK_a value of propionic acid, a food preservative. 

Using your knowledge of important pK_a values, estimate the pK_a value of the indicated proton and explain your choice.

Given the structure of 2-ethyl-2,5,5-trimethylpyrrolidin-1-ide, show its conjugate acid and choose the pK _a value from the table that could help predict the stability of the base.

For the given base, show the conjugate acid and select the pK  _a value from the table that could aid in determining the stability of the base.

a. Two unknown acids, A and B, have pK_a values of 4.5 and 5.0, respectively. Determine which one is a stronger acid.
b. Similarly, two unknown acids, X and Y, correspond to the acid dissociation constants of 2.9 x 10⁻⁴ and 1.3 x 10⁻⁵, respectively. Determine which one is a stronger acid.

Provide approximate pK_a values for the species given below.

a. CH₃CH₂NH₃⁺

b. CH₃COOH

Arrange the 1.00 M aqueous solutions of the acids listed below in order of increasing acidity.

HF       pK_a = 3.17

HCN    pK_a = 9.22

CH₄     pK_a = 50.0

The pK_a value of chlorous acid, HClO₂, is 1.94. This makes it almost 290,000 times more acidic than hypochlorous acid, HClO, with a pK_a value of 7.40. Why is HClO₂ stronger than HClO in terms of acidity?

Ethaneperoxoic acid, C₂H₄O₃, has a pK_a value of 8.20. It is a weaker acid when compared to ethanoic acid, C₂H₄O₂ (pK_a = 4.74). Why is ethaneperoxoic acid weaker than ethanoic acid in terms of acidity?