Rules for Learning the Solubility of Ionic Compounds in Water |
Negative Ions
(Anions) |
+ |
Positive Ions
(Cations) |
= |
Solubility of compounds in water |
Example |
| any anion |
+ |
alkali ions
(Li+,Na+,K+,Rb+,Cs+,Fr+) |
= |
soluble |
sodium fluoride, NaF, is soluble |
| any anion |
+ |
hydrogen ion
[H+(aq)] |
= |
soluble |
hydrogen chloride, HCl, is soluble |
| any anion |
+ |
amonium ion
(NH4+) |
= |
soluble |
ammonium chloride, NH4Cl, is soluble |
nitrate
NO3- |
+ |
any cation |
= |
soluble |
potassium nitrate, KNO3, is soluble |
acetate
(CH3COO-) |
+ |
any cation |
= |
soluble |
sodium acetate, CH3COONa, is soluble |
| Chloride (Cl-), Bromide (Br-), Iodide (I-) |
+ |
silver (Ag+), lead (Pb2+), mercury (Hg2+), copper (Cu+), thallium (Tl+) |
= |
low solubility (insoluble) |
silver chloride, AgCl, forms a white precipitate (a white solid) |
| + |
any other cation |
= |
soluble |
potassium bromide, KBr, is soluble |
Sulphate
(SO42-) |
+ |
calcium (Ca2+), strontium (Sr2+), barium (Ba2+), silver (Ag+), lead (Pb2+), radium (Ra2+) |
= |
low solubility (insoluble) |
barium sulphate, BaSO4, forms a white precipitate (a white solid) |
| + |
any other cation |
= |
soluble |
copper sulphate, CuSO4, is soluble |
Sulfide
S2- |
+ |
alkali ions (Li+,Na+,K+,Rb+,Cs+,Fr+), alkali earth metals (Be2+,Mg2+,Ca2+,Sr2+,Ba2+,Ra2+),
and H+(aq), NH4+ |
= |
soluble |
magnesium sulfide, MgS, is soluble |
| + |
any other cation |
= |
low solubility (insoluble) |
zinc sulfide, ZnS, is insoluble |
Hydroxide
OH- |
+ |
alkali ions (Li+,Na+,K+,Rb+,Cs+,Fr+), H+(aq),NH4+,Sr2+,Ba2+,Ra2+,Tl+ |
= |
soluble |
strontium hydroxide,
Sr(OH)2, is soluble |
| + |
any other cation |
= |
low solubility (insoluble) |
silver hydroxide, AgOH, is insoluble (forms a precipitate) |
| Phosphate, PO43-, Carbonate, CO32-, sulphite, SO32- |
+ |
alkali ions (Li+,Na+,K+,Rb+,Cs+,Fr+), H+(aq),NH4+ |
= |
soluble |
ammonium phosphate,
(NH4)3PO4, is soluble |
| + |
any other cation |
= |
low solubility (insoluble) |
magnesium carbonate, MgCO3, is insoluble |
- All compounds of the ammonium ion (NH4+), and of Alkali metal (Group IA) cations, are soluble.
- All nitrates and acetates (ethanoates) are soluble.
- All chlorides, bromides and iodides are soluble EXCEPT those of silver, lead and mercury(I).
- All sulphates are soluble EXCEPT those of silver, lead, mercury(I), barium, strontium and calcium.
- All carbonates, sulfites and phosphates are insoluble EXCEPT those of ammonium and Alkali metal (Group IA) cations.
- All hydroxides are insoluble EXCEPT those of ammonium, barium and alkali metal (Group I) cations.
- All sulfides are insoluble EXCEPT those of ammonium, Alkali metal (Group I) cations and Alkali earth metal (Group II) cations.
- All oxides are insoluble EXCEPT those of calcium, barium and Alkali metal (Group I) cations; these soluble ones actually react with the water to form hydroxides (hydrolyse).
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