What is the pH of a 0.501 M aqueous solution of hypochlorous acid, for which Ka=3.5 ×10^-8 ?

Name: Problem 72, Chapter 18: Introductory Chemistry: An Active Learning Approach
Uploaded: 2020-10-25T00:10:34-08:00
Duration: 1 min 46 s
Channel: David Collins
Description: What is the pH of a 0.501 M aqueous solution of hypochlorous acid, for which Ka=3.5 ×10^-8 ?

step 1 Question number 72 is a pH calculation of a weak acid given the concentration of the weak acid a

What is the pH of a 0.501 M aqueous solution of hypochlorous...

Key Concepts

Approximation Techniques in Equilibria

When dealing with weak acids, the extent of dissociation is typically very small relative to the initial acid concentration. This allows the use of approximation techniques, where the change in concentration (often represented as x) is assumed to be negligible compared to the initial concentration, thereby simplifying the algebra. Such approximations make it easier to calculate the hydrogen ion concentration without resorting to solving a full quadratic equation.

The concept of pH represents a measure of the acidity or basicity of a solution. It is defined as the negative logarithm of the hydrogen ion concentration, [H?], in a solution. Understanding pH is crucial because it provides insight into the reactivity, chemical behavior, and environmental impact of a substance in an aqueous medium.

Acid Dissociation Constant (Ka)

The acid dissociation constant, Ka, is a quantitative measure of the strength of an acid in solution. A smaller Ka value indicates a weak acid that only partially dissociates into its ions when dissolved in water. This constant is used to set up equilibrium expressions for weak acid dissociation reactions and is instrumental in calculating the degree of ionization and the resulting [H?] concentration.

Weak Acid Equilibrium

Weak acid equilibrium involves the reversible dissociation of a weak acid in water into its conjugate base and hydrogen ion. In calculating equilibrium concentrations, an equilibrium expression derived from the Ka is established, often resulting in a quadratic equation where the change in concentration can be approximated under the assumption that the degree of dissociation is small compared to the initial concentration.

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