Solubility Product Calculations

Learning Objectives

• Ksp Expression: Write Ksp expression for ionization of salts.
• Ksp Calculations: Calculate Ksp from solubility and vice versa.
• Precipitation Prediction: Determine if a precipitate forms when solutions are mixed.
• Separation of Metal Ions: Predict separation by precipitation of hydroxides or salts.
• Complexing Agents: Determine if they will dissolve metal precipitates.
• Common Ion Effect: Understand its impact on solubility.

Importance of Solubility Product

• Solubility Calculation: Solubility product helps calculate solubility of salts like AgCl.
• Precipitation Prediction: Indicates if precipitation occurs upon mixing solutions.
• Inorganic Analysis: Essential in separation of cations in qualitative analysis.
• Purification: Used in purification processes like sodium chloride from sea water.

Solubility Product Concept

• Ksp Definition: Ksp is reached in a saturated solution; exceeding Ksp leads to precipitation.
• Dissociation Equation: Example - Al2S3 dissociates into ions, expressed as Ksp = [Al3+]²[S2-]³.

Factors Affecting Solubility

Temperature

• Endothermic: Solubility increases with temperature.
• Exothermic: Solubility decreases with temperature.

Solvent

• Polar vs Non-Polar: Solubility depends on the nature of solute and solvent.

Common Ion Effect

• Decreases Solubility: Presence of common ion reduces solubility of ionic compounds.

Ionic Strength

• Opposite Effect: Uncommon ions can increase Ksp value.

pH Effect

• Metal Hydroxides & Weak Salts: Solubility affected by the solution's pH.

Calculation Examples

• Example 1: Solubility of Ag2CrO4 using its Ksp.
• Example 2: Precipitation prediction using ion product (Q) vs Ksp.
• Example 3: Calculating Ksp from molar solubility.

Complex Ions and Solubility

• Complexation: This can increase solubility of metal ion salts.
• Example: AgCl dissolves in NH3 due to complexation.

General Solubility Rules

1. Group 1 elements and NH4+ salts are soluble.
2. Common acetates and nitrates are soluble.
3. Binary compounds of Group 17 are soluble except with Ag+, Hg2+, Pb2+.
4. Sulfates are soluble except with Ca2+, Sr2+, Ba2+, Ag+, Hg2+, Pb2+.
5. Carbonates, hydroxides, oxides, and phosphates are insoluble except as per rule 1.

Summary

• Ksp Concepts: Key for analytical chemistry, predicting precipitation, and understanding solubility factors.
• Factors: Includes temperature, common ion, ionic strength, pH, and complex formation.
• Applications: Separation of metal ions via stepwise precipitation.

Tutorial Exercises:

1. AgCl Ksp: Calculate molar solubility.
2. Cr(OH)3 Molar Solubility: From Ksp.
3. Bi2S3 Ksp: From molar solubility.
4. CaF2 Solubility in g/L: From Ksp.
5. MgC2O4 Precipitation: Determine if it precipitates.
6. PbCl2 Solubility in HCl: Investigate common ion effect.
7. Fe(OH)3 Precipitation pH: Calculate starting and completion pH.
8. Separation by Precipitation: Using pH to separate Mn2+ and Fe3+.