Solubility Rules
Water is the most common solvent. Since we use it a lot, we have found that ionic compounds tend to dissolve in water quite well due to polarity issues. However, some ionic compounds are quite soluble and others are quite insoluble. This is usually based on the ions present in the compounds — some ions are more soluble than others. To determine Solubility, we use a set of common rules to determine the solubility of ionic compounds in water. With each rule, though, be aware that there could be some exceptions:
Soluble ions
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Exceptions
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Nitrate (NO3-1)
Alkali Metals (Li+1, Na+1, K+1, Rb+1, Cs+1) Ammonium (NH4+1) Acetate (C2H3O2-1) Sulfate (SO4-2) Halogen Ions (Cl-1, Br-1, I-1) |
None
None None None BaSO4, SrSO4, PbSO4 AgX, PbX2, Hg2X2 |
Insoluble Ions
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Exceptions
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Phosphate (PO4-3)
Chromate (CrO4-2) Carbonate (CO3-2) Sulfide (S-2) Hydroxide (OH-1) Flouride (F-1) |
Alkali metals and ammonium with phosphate
Alkali metals and ammonium with chromate Alkali metals and ammonium with carbonate Alkali metals and ammonium with sulfude Alkali metals and ammonium with hydroxide Alkali metals and ammonium with fluoride |
in general, most ionic compounds will fit under one of the above rules. If you come across a compound that doe not fit under one of the above rules, there are two more rules you can use:
1) If the negative ion in the compound is -1, then the substance is most alikely soluble in water.
2) If the negative ion in the compound is -2, -3 or -4, then the substance is most likely insoluble in water.
Although these last two rules aren’t perfect, they can be used to make decent guesses.
1) If the negative ion in the compound is -1, then the substance is most alikely soluble in water.
2) If the negative ion in the compound is -2, -3 or -4, then the substance is most likely insoluble in water.
Although these last two rules aren’t perfect, they can be used to make decent guesses.