Solubility Rules

Use these relationships to determine whether a double displacement reaction will result in the formation of a precipitate (ppt).

Keep these relationships in mind as we are doing qualitative analysis.

Solubility Rules
1	All chlorides, bromides, and iodides are soluble except those containing Ag⁺, Pb²⁺, or Hg₂²⁺.
2	All compounds containing NO₃^-, ClO₄^-, ClO₃^-, and C₂H₃O₂^- anions are soluble.
3	All sulfates (SO₄^-2) are soluble except those containing Hg₂²⁺, Pb²⁺, Sr²⁺, Ca²⁺, or Ba²⁺.
4	All compounds containing alkali metal cations (Na+, K+, H+) and the ammonium ion (NH4+) are soluble
5	All compounds containing OH^-, PO₄^3-, S^2-, CO₃^2-, O^2-,CrO₄^-2 and SO₃^2-ions are insoluble, unless the cation is from Rule 4. (Rule 4 is stronger than Rule 5)

Solubility reactions. A double displacement reaction will "fail" if

One or more of the reactants are insoluble. Example: PbS + AgNO3 --> Fails by rule 5 S²- compounds are insoluble. No reaction.
If both products are soluble. Example: NaCl + HC2H3O2 --> NaC₂H₃O₂ + HCl No reaction. No ppt. Rule 2 and Rule 4