Ch.16 - Acid-Base Equilibria

Brown - Chemistry: The Central Science 15th Edition

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Brown 15th Edition

Ch.16 - Acid-Base Equilibria

Problem 32b

Chapter 16, Problem 32b

Write the expression for the ion product constant for water, K_w.

Name: Chemistry: The Central Science
Author: Brown
ISBN: 9780137542970

Verified step by step guidance

Understand that the ion product constant for water, denoted as \( K_w \), is a special equilibrium constant for the self-ionization of water.

Recognize the self-ionization reaction of water: \( 2H_2O(l) \rightleftharpoons H_3O^+(aq) + OH^-(aq) \).

Simplify the reaction to: \( H_2O(l) \rightleftharpoons H^+(aq) + OH^-(aq) \), where \( H^+ \) is often used interchangeably with \( H_3O^+ \).

Write the expression for the equilibrium constant \( K_w \) as the product of the concentrations of the ions: \( K_w = [H^+][OH^-] \).

Note that \( K_w \) is temperature-dependent and at 25°C, \( K_w \) is typically \( 1.0 \times 10^{-14} \).

Key Concepts

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

Ion Product Constant for Water (Kw)

The ion product constant for water, denoted as Kw, is the equilibrium constant for the self-ionization of water. It is defined as the product of the concentrations of hydrogen ions [H+] and hydroxide ions [OH-] in pure water at a given temperature. At 25°C, Kw is equal to 1.0 x 10^-14, indicating that the concentrations of H+ and OH- are both 1.0 x 10^-7 M in neutral water.

Self-Ionization of Water

Self-ionization of water refers to the process where two water molecules react to form one hydronium ion (H3O+) and one hydroxide ion (OH-). This reaction is represented by the equation: 2 H2O ⇌ H3O+ + OH-. This equilibrium is crucial for understanding acid-base chemistry, as it establishes the basis for the pH scale and the behavior of acids and bases in aqueous solutions.

Acid-Base Equilibrium

Acid-base equilibrium involves the balance between acids and bases in a solution, which is influenced by the concentrations of H+ and OH- ions. The pH scale, which ranges from 0 to 14, is a logarithmic scale that measures the acidity or basicity of a solution based on the concentration of H+. Understanding this equilibrium is essential for predicting how substances will behave in solution and for calculating pH and pOH.

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Related Practice

Textbook Question

Predict the products of the following acid–base reactions, and predict whether the equilibrium lies to the left or to the right of the reaction arrow:

(a) NH₄⁺(aq) + OH^-(aq) ⇌

(b) CH₃COO^-(aq) + H₃O⁺(aq) ⇌

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Textbook Question

Deuterium oxide 1D2O, where D is deuterium, the hydrogen-2 isotope) has an ion-product constant, Kw, of 8.9 * 10-16 at 20 °C. Calculate 3D+4 and 3OD-4 for pure (neutral) D2O at this temperature.

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Textbook Question

Predict the products of the following acid–base reactions, and predict whether the equilibrium lies to the left or to the right of the reaction arrow:

(a) O^2-(aq) + H₂O(l) ⇌

(b) CH₃COOH(aq) + HS^-(aq) ⇌

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Textbook Question

Write a chemical equation that illustrates the autoionization of water.

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Textbook Question

Calculate 3OH-4 for each of the following solutions, and indicate whether the solution is acidic, basic, or neutral: (a) 3H+4 = 0.0505 M

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