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Question

A solution of hypochlorous acid, HOCl, which has a known Ka of 3.5 x 10-8 is placed in a flask.

1.Write the hydrolysis reaction of hypochlorous acid.

2.Write the acid dissociation expression for this acid.

3.If the pH in the flask is measured at 3.58, what is the initial concentration of the hypochlorous acid?

4.Calculate the percent dissociation of the hypochlorous acid in solution.

Lactic acid is an acid found in many dairy-related products. To control the pH level of lactic acid containing substances, sodium lactate, NaC3H5O3, is often used.

1. Is sodium lactate an acidic salt, basic salt, or neutral salt? Justify your answer.

2.The Ka for lactic acid is 1.38 x 10-4. What is the Kb of lactate?

Answer 1

1). HOCl +H2O ==> H3O⁺ + ClO^-

2). Ka = 3.5x10^-8 = [H3O⁺][ClO^-] / [HOCl]

3). pH = 3.58; [H3O⁺] = 1x10^-3.58 = 2.63x10^-4 M which is also the [ClO^-]

3.5x10^-8 = (2.63x10^-4)² / [HOCl]

[HOCl] = 6.9x10^-8 / 3.5x10^-8 = 1.98 M

4). % dissociation = 2.63x10^-4 / 1.98 (x100%) = 0.013%

Lactic acid:

1). Sodium lactate is a basic salt because it is the salt of a weak acid (lactic acid) and a strong base (NaOH)

2). KaKb = Kw

1.38x10^-4 Kb = 1x10^-14

Kb = 1x10^-4 / 1.38x10^-14

Kb = 7.25x10^-9