Ch.16 - Acid-Base Equilibria

Brown - Chemistry: The Central Science 14th Edition

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Brown 14th Edition

Ch.16 - Acid-Base Equilibria

Problem 77c

Chapter 16, Problem 77c

Calculate Kb values for CH3COO- and ClO-.

Verified step by step guidance

Identify the chemical species involved and their corresponding acid forms. For CH3COO-, the acid form is CH3COOH (acetic acid). For ClO-, the acid form is HClO (hypochlorous acid).

Look up or calculate the Ka values for the corresponding acids. Ka for acetic acid (CH3COOH) and Ka for hypochlorous acid (HClO) are needed.

Use the relationship between Ka, Kb, and Kw to find Kb. The formula to use is Kb = \( \frac{Kw}{Ka} \), where Kw is the ion-product constant of water at 25°C, typically \( 1 \times 10^{-14} \).

Calculate the Kb for CH3COO- by substituting the Ka value of acetic acid into the formula.

Calculate the Kb for ClO- by substituting the Ka value of hypochlorous acid into the formula.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Base Ionization Constant (Kb)

The base ionization constant (Kb) is a measure of the strength of a base in solution. It quantifies the extent to which a base can accept protons from water, forming hydroxide ions (OH-) and the corresponding conjugate acid. A higher Kb value indicates a stronger base, as it signifies a greater tendency to ionize in solution.

Conjugate Base

A conjugate base is the species that remains after an acid donates a proton (H+). In the context of the question, CH3COO- (acetate) is the conjugate base of acetic acid (CH3COOH), and ClO- (hypochlorite) is the conjugate base of hypochlorous acid (HClO). Understanding the relationship between acids and their conjugate bases is essential for calculating Kb values.

Water's Role in Acid-Base Reactions

Water acts as both an acid and a base in acid-base reactions, facilitating the transfer of protons. In the context of calculating Kb, water's role is crucial as it provides the medium in which the base ionizes. The equilibrium established between the base, its conjugate acid, and water is fundamental to determining the Kb value, as it reflects the balance of concentrations at equilibrium.

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