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💏intro to chemistry review

Acid-Base Theory

Written by the Fiveable Content Team • Last updated August 2025
Written by the Fiveable Content Team • Last updated August 2025

Definition

Acid-base theory is a fundamental concept in chemistry that describes the behavior of acids and bases, their properties, and their interactions. It provides a framework for understanding the transfer of protons (H+ ions) in chemical reactions and the resulting changes in pH.

Acid-Base Theory cheat sheet for homework

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5 Must Know Facts For Your Next Test

  1. Acid-base reactions involve the transfer of protons (H+ ions) between an acid and a base, resulting in the formation of a conjugate acid-base pair.
  2. The strength of an acid or base is determined by its ability to donate or accept protons, respectively, which is measured by the acid dissociation constant (Ka) or base dissociation constant (Kb).
  3. Polyprotic acids, such as phosphoric acid (H3PO4), can donate multiple protons, leading to the formation of different conjugate acid-base pairs at different pH levels.
  4. The pH of a solution is a measure of the concentration of hydrogen ions (H+) and is calculated as the negative logarithm of the hydrogen ion concentration.
  5. Buffers are solutions that resist changes in pH when small amounts of an acid or base are added, maintaining a relatively stable pH.

Review Questions

  • Explain the key differences between the Arrhenius and Brønsted-Lowry acid-base theories.
    • The Arrhenius acid-base theory defines acids as substances that produce hydrogen ions (H+) in aqueous solutions, and bases as substances that produce hydroxide ions (OH-) in aqueous solutions. In contrast, the Brønsted-Lowry acid-base theory defines acids as proton donors and bases as proton acceptors, allowing for the identification of conjugate acid-base pairs. The Brønsted-Lowry theory is more comprehensive, as it can account for acid-base reactions in non-aqueous solutions and the formation of different conjugate acid-base pairs at different pH levels.
  • Describe the relationship between pH and the concentration of hydrogen ions (H+) in a solution.
    • The pH of a solution is a measure of the concentration of hydrogen ions (H+) present. Specifically, pH is defined as the negative logarithm of the hydrogen ion concentration, or pH = -log[H+]. This means that as the concentration of H+ increases, the pH decreases, and vice versa. A pH of 7 is considered neutral, with [H+] = 1.0 × 10^-7 M. Solutions with pH values less than 7 are considered acidic, while solutions with pH values greater than 7 are considered basic or alkaline.
  • Explain the role of buffers in maintaining a stable pH and how they function in the context of acid-base theory.
    • Buffers are solutions that resist changes in pH when small amounts of an acid or base are added. They function by providing a reserve of protons (H+) or hydroxide ions (OH-) that can neutralize added acids or bases, respectively, maintaining a relatively stable pH. Buffers work by the principle of Le Chatelier's principle, where the system will shift to counteract any changes in the concentration of reactants or products. In the context of acid-base theory, buffers allow for the maintenance of a desired pH range, which is crucial in many biological and chemical processes.
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