Understanding Solubility Rules in Chemistry

Feb 25, 2025

Chem 115 - Lecture Notes (September 28, 2020)

Introduction

  • Focus on solubility rules for ionic compounds in solution chemistry.

Solubility Rules

Rule #1: Soluble with Six Positive Ions

  • Positive ions: Group 1A metals (Lithium, Sodium, Potassium, Rubidium, Cesium) and Ammonium.
  • When these ions are present, the compound is a soluble ionic compound that fully dissociates in solution.

Rule #2: Soluble with Six Negative Ions

  • Negative ions: Nitrate, Nitrite, Chlorate, Perchlorate, Acetate, Bicarbonate.
  • Compounds with these ions are soluble, regardless of the positive ion.

Rule #3: Soluble with Exceptions (Halides)

  • Chloride, Bromide, and Iodide are soluble except with Silver (Ag), Lead (Pb2+), and Mercury I (Hg2+).
  • These exceptions result in insoluble compounds (precipitates).

Rule #4: Soluble with Exceptions (Sulfates)

  • Sulfates are generally soluble except with Silver, Lead, Mercury I, Calcium, Strontium, and Barium.
  • These exceptions are insoluble and form precipitates.

Rule #5: Insoluble with Exceptions (Oxides and Hydroxides)

  • Oxides and Hydroxides are typically insoluble, except when combined with Group 1A metals or Calcium, Strontium, and Barium.
  • These exceptions are soluble and form strong bases.

Rule #6: Insoluble (Everything Else)

  • Ions like Fluoride, Sulfide, Carbonate, Phosphate, Chromate are insoluble except with Group 1A or Ammonium.

Application of Solubility Rules

  • Example: Combining strong electrolytes can sometimes result in no reaction if all products are soluble.
  • Important to identify precipitates: If no precipitate forms, no reaction occurs.

Special Cases

Mercury I Ion (Hg2+)

  • Behaves as a polyatomic ion due to a covalent bond between mercury atoms.
  • Unique behavior with chloride, bromide, and iodide ions.

Reaction Types

  • Double Displacement Reactions: Require a precipitate, molecular compound, or weak electrolyte to occur.

Practical Guidelines

  • Memorization: Essential for solubility rules to quickly determine the outcomes of chemical reactions.
  • Net Ionic Equations: Only formed when products result in precipitates, weak electrolytes, or molecular compounds.

Conclusion

  • Solubility rules simplify the understanding of which compounds dissolve in solution, crucial for predicting chemical reaction outcomes.
  • Knowledge of these rules is essential for exams and practical applications in chemistry.

Next Steps

  • Further discussion on double displacement reactions and their specific conditions.

These notes summarize key points from the lecture on solubility rules and their applications in chemistry, focusing on the prediction of soluble and insoluble compounds in chemical reactions.