Precipitation Reactions
Solubility Rules
1. All compounds containing either the Na+, NH4+, K+ or NO3- ion will dissolve in water.
Compounds containing these ions never form precipitates.
Eg. NaCl, NaNO3, NH4Cl, K2SO4 and AgNO3 are all soluble in water and never form
precipitates.
2. All compounds containing the Chloride (Cl- ), Bromide(Br-)and Iodide(I- )ions are soluble in
water, except when they form compounds with Silver(Ag+ ), Lead(Pb2+ )and Mercury
(Hg2+ )ions.
Eg. AgCl, PbBr2, HgCl2 are all insoluble
FeCl2, ZnBr2 and AlCl3 are all soluble.
3. Compounds containing the sulfate(SO4-2 ) ion are soluble except for BaSO4, PbSO4 and CaSO4.
4. Compounds containing carbonate (CO3-2) and phosphate (PO4-3) are insoluble except when
they contain the ions sodium (Na+ ), Potassium (K+ )and Ammonium(NH4+).
Eg. Sodium Carbonate is soluble but Barium carbonate is insoluble.
5. Compounds containing Hydroxide(OH- )ions are insoluble, except if they contain sodium
(Na+), potassium (K+) or ammonium ions(NH4+).
6. Some compounds are slightly soluble eg. Calcium hydroxide(Ca(OH)2, lead chloride(PbCl2),
lead bromide(PbBr2),calcium sulphate(CaSO4) and silver sulphate(Ag2SO4).
Precipitation Reactions
Solubility Rules
1. All compounds containing either the Na+, NH4+, K+ or NO3- ion will dissolve in water.
Compounds containing these ions never form precipitates.
Eg. NaCl, NaNO3, NH4Cl, K2SO4 and AgNO3 are all soluble in water and never form
precipitates.
2. All compounds containing the Chloride (Cl- ), Bromide(Br-)and Iodide(I- )ions are soluble in
water, except when they form compounds with Silver(Ag+ ), Lead(Pb2+ )and Mercury
(Hg2+ )ions.
Eg. AgCl, PbBr2, HgCl2 are all insoluble
FeCl2, ZnBr2 and AlCl3 are all soluble.
3. Compounds containing the sulfate(SO4-2 ) ion are soluble except for BaSO4, PbSO4 and CaSO4.
4. Compounds containing carbonate (CO3-2) and phosphate (PO4-3) are insoluble except when
they contain the ions sodium (Na+ ), Potassium (K+ )and Ammonium(NH4+).
Eg. Sodium Carbonate is soluble but Barium carbonate is insoluble.
5. Compounds containing Hydroxide(OH- )ions are insoluble, except if they contain sodium
(Na+), potassium (K+) or ammonium ions(NH4+).
6. Some compounds are slightly soluble eg. Calcium hydroxide(Ca(OH)2, lead chloride(PbCl2),
lead bromide(PbBr2),calcium sulphate(CaSO4) and silver sulphate(Ag2SO4).