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pH and Solubility

Ethan Taylor

Ethan Taylor

7 min read

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Study Guide Overview

This study guide covers how pH affects solubility using Le Chatelier's Principle. It explains the impact of acidic and basic solutions on compounds with basic or acidic conjugate bases, the common ion effect, and why pH-neutral compounds are generally unaffected. It includes examples, practice questions, and emphasizes qualitative understanding over calculations for the AP exam.

pH and Solubility: A Last-Minute Review 🚀

Hey, you've got this! Let's quickly review how pH affects solubility, focusing on the key ideas you'll need for the AP exam. Remember, it's all about how equilibrium shifts with changing conditions.

The Big Picture: pH, Solubility, and Equilibrium

  • pH tells us the concentration of H⁺ (and OH⁻) ions in a solution.
  • Solubility is all about how much of a substance dissolves in a solution, and it's an equilibrium process. ⚖️
  • Le Chatelier's Principle is our guide: If we change a condition (like pH), the equilibrium will shift to counteract that change.
  • The common ion effect can also influence solubility by adding an ion that's already part of the equilibrium.

### Effects of Acidic Solutions 🍋

  • Key Idea: Acidic solutions (high [H⁺]) generally increase the solubility of compounds with basic conjugate bases.
  • Why? The H⁺ ions react with the basic conjugate base (A⁻) to form HA, reducing [A⁻], and shifting the equilibrium towards dissolution.
    • A+H+HAA^- + H^+ \rightleftharpoons HA
  • The weaker the acid, the more basic its conjugate base, and the more its solubility is affected by pH.
  • Example: Fe(OH)₃ solubility increases in acidic solutions because H⁺ ions react with OH⁻, reducing [OH⁻] and pushing the dissolution equilibrium to the right.
    • Fe(OH)3Fe3++3OHFe(OH)_3 \rightleftharpoons Fe^{3+} + 3OH^-
    • H++OHH2OH^+ + OH^- \rightleftharpoons H_2O

Exam Tip

Remember: More basic anions = more soluble in acidic solutions. Think of it like opposites attracting! 🧲


<img src="https://zupay.blob.core.windows.net/resources/files/0baca4f69800419293b4c75aa2870acd_5f0572_3124.png?alt=media&token=54c68b48-a9db-49ea-80ef-60b0...

Question 1 of 12

What does pH primarily indicate about a solution? 🤔

The total number of ions

The concentration of H⁺ and OH⁻ ions

The mass of the solute

The temperature of the solution