Solubility Rule
Solubility rules are a set of guidelines that help predict whether an ionic compound will dissolve (be soluble) in water. They are essential in chemistry for determining the outcome of reactions, especially when dealing with precipitation reactions.
General Solubility Rules
- All salts of Group 1 elements (Li⁺, Na⁺, K⁺, etc.) and ammonium ion (NH₄⁺) are soluble.
- All nitrates (NO₃⁻), acetates (CH₃COO⁻), and perchlorates (ClO₄⁻) are soluble.
- Chlorides (Cl⁻), bromides (Br⁻), and iodides (I⁻) are generally soluble.
- Sulfates (SO₄²⁻) are mostly soluble.
- Hydroxides (OH⁻), carbonates (CO₃²⁻), phosphates (PO₄³⁻), and sulfides (S²⁻) are generally insoluble.
Common Exceptions to the Rules
- Silver (Ag⁺), lead (Pb²⁺), and mercury (Hg₂²⁺) form insoluble halides and sulfates.
- Calcium (Ca²⁺), barium (Ba²⁺), and strontium (Sr²⁺) sulfates and hydroxides are poorly soluble.
- Some transition metal compounds also deviate from expected solubility due to complex ion formation or lattice energy.
Applications
Solubility rules help in:
- Predicting whether a precipitate will form in a double displacement reaction.
- Designing chemical separation techniques.
- Understanding solubility equilibria in qualitative analysis.
These rules are not absolute, but they provide a reliable foundation for analyzing ionic behavior in aqueous solutions.