Lesson: Solubility Equilibrium

Introduction

Solubility equilibrium refers to the dynamic balance between the dissolution of a solute and its precipitation in a saturated solution. This concept is crucial in understanding how substances inte\fract in solution and the factors that affect solubility.

Key Concepts

• Saturated Solution: A solution that contains the maximum concentration of a solute at a given temperature and pressure.
• Solubility Product Constant ($K_{sp}$): An equilibrium constant that applies to the solubility of ionic compounds. It is expressed as:

$K_{sp} = [A^{+}]^m[B^{-}]^n$

where $A^{+}$ and $B^{-}$ are the ions produced from the solute, and $m$ and $n$ are their respective coefficients in the balanced equation.

Example: Solubility of Silver Chloride ($AgCl$)

1. The dissociation of silver chloride in water can be represented as: $AgCl(s) \rightleftharpoons Ag^{+}(aq) + Cl^{-}(aq)$
2. The solubility product expression is: $K_{sp} = [Ag^{+}][Cl^{-}]$
3. If the solubility of $AgCl$ is $s$, then: $[Ag^{+}] = s \ and \ [Cl^{-}] = s$
4. Thus, we can write: $K_{sp} = s \times s = s^{2}$

Factors Affecting Solubility

• Temperature: Solubility generally increases with temperature for solids but decreases for gases.
• Common Ion Effect: The presence of a common ion decreases the solubility of a salt.
• pH: Changes in pH can affect the solubility of salts, particularly those containing basic or acidic ions.

Key Questions

• What is the difference between a saturated solution and an unsaturated solution?
• How do temperature changes affect the solubility of salts?
• What is the common ion effect, and how does it influence solubility?
• How can you calculate the solubility product constant for a given salt?

Conclusion

Understanding solubility equilibrium is essential for predicting the behavior of ionic compounds in solution, which has implications in various fields including environmental chemistry, pharmaceuticals, and materials science.