Solubility Rules
* Generally Soluble:
* Group 1 cations (Li+, Na+, K+, Rb+, Cs+)
* Ammonium (NH₄⁺)
* Nitrates (NO₃⁻)
* Chlorides (Cl⁻), Bromides (Br⁻), Iodides (I⁻) - Exceptions: Ag⁺, Pb²⁺, Hg₂²⁺
* Sulfates (SO₄²⁻) - Exceptions: Ca²⁺, Sr²⁺, Ba²⁺, Pb²⁺
* Generally Insoluble:
* Carbonates (CO₃²⁻) - Exceptions: Group 1 cations, NH₄⁺
* Phosphates (PO₄³⁻) - Exceptions: Group 1 cations, NH₄⁺
* Hydroxides (OH⁻) - Exceptions: Group 1 cations, Ba²⁺, Sr²⁺, Ca²⁺
Analysis
* KC₂H₃O₂ (Potassium Acetate): Soluble (Group 1 cation)
* CaSO₄ (Calcium Sulfate): Insoluble (Exception to sulfate rule)
* SrS (Strontium Sulfide): Soluble (Sulfides are generally soluble, not an exception)
* AlPO₄ (Aluminum Phosphate): Insoluble (General rule for phosphates)
Conclusion
Two of the compounds are insoluble in water: CaSO₄ and AlPO₄.
