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Ch.16 - Acid-Base Equilibria
Brown - Chemistry: The Central Science 15th Edition
Brown15th EditionChemistry: The Central ScienceISBN: 9780137542970Not the one you use?Change textbook
All textbooksBrown 15th EditionCh.16 - Acid-Base EquilibriaProblem 32a
Chapter 16, Problem 32a

Write a chemical equation that illustrates the autoionization of water.

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1
Identify the process of autoionization of water, which involves water molecules reacting with each other to form ions.
Write the chemical formula for water: \( \text{H}_2\text{O} \).
Recognize that in autoionization, one water molecule donates a proton (\( \text{H}^+ \)) to another water molecule.
Write the chemical equation for the autoionization: \( 2\, \text{H}_2\text{O}(l) \rightleftharpoons \text{H}_3\text{O}^+(aq) + \text{OH}^-(aq) \).
Understand that this equilibrium process is essential for the concept of pH and the self-ionization constant of water, \( K_w \).

Key Concepts

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

Autoionization of Water

Autoionization of water refers to the process where two water molecules interact to produce hydronium (H3O+) and hydroxide (OH-) ions. This reaction is essential in understanding the behavior of water as both an acid and a base, and it establishes the foundation for the pH scale, which measures the acidity or basicity of solutions.
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Chemical Equations

A chemical equation is a symbolic representation of a chemical reaction, showing the reactants and products along with their respective quantities. In the case of the autoionization of water, the equation is represented as 2 H2O ⇌ H3O+ + OH-, indicating that water can dissociate into its ionic components in a reversible manner.
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Equilibrium in Chemical Reactions

Equilibrium in chemical reactions occurs when the rates of the forward and reverse reactions are equal, resulting in constant concentrations of reactants and products. For the autoionization of water, this equilibrium is crucial as it determines the concentrations of H3O+ and OH- ions in pure water, which are both 1.0 x 10^-7 M at 25°C, leading to a neutral pH of 7.
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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) ⇌

(c) HCO3-(aq) + F-(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) O2-(aq) + H2O(l) ⇌

(b) CH3COOH(aq) + HS-(aq) ⇌

(c) NO2-(aq) + H2O(l) ⇌

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Textbook Question

Which of the following is the stronger Brønsted–Lowry acid, HBrO or HBr?

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Textbook Question

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

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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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