Whether a salt dissolves decides how you make it. Learn a short list of solubility rules, and you can predict which pairs of solutions will produce a precipitate and how to collect it.
General rules: all sodium, potassium and ammonium salts are soluble; all nitrates are soluble; chlorides are soluble except silver and lead(II) chlorides; sulfates are soluble except barium, calcium and lead(II) sulfates; carbonates and hydroxides are insoluble except those of sodium, potassium and ammonium (calcium hydroxide is slightly soluble). Extended: an insoluble salt is made by precipitation: mix two solutions that contain its ions, then filter, wash and dry the precipitate.
Compare the solubilities of the Group 2 hydroxides and sulfates in the simulator; they follow opposite trends, which is why barium sulfate is insoluble.
| Compounds | Soluble | Insoluble (common exceptions) |
|---|---|---|
| sodium, potassium, ammonium | all | none |
| nitrates | all | none |
| chlorides (and bromides, iodides) | most | silver, lead(II) |
| sulfates | most | barium, calcium, lead(II) |
| carbonates | sodium, potassium, ammonium | all others |
| hydroxides | sodium, potassium, ammonium; calcium slightly | all others |
Four quick checks. Each correct answer earns XP and records this skill on your profile.
Which salt is insoluble in water?
Which statement about nitrates is correct?
Which carbonate is soluble in water?
(Extended) An insoluble salt is best prepared by:
Extended. Choose one soluble compound that provides the cation and another that provides the anion. When the solutions are mixed, the insoluble salt comes out of solution as a precipitate.
For an insoluble salt the product you want is the residue on the filter paper, not the filtrate: the opposite of the soluble salt method. Nitrates are useful starting materials because they are always soluble; for example, use lead(II) nitrate, not lead(II) chloride, as the source of lead ions.
Unlocks once the four checks above are done. Worth more XP, written to IGCSE Paper 2 and Paper 4 standard.
(Extended) Which pair of solutions would produce a precipitate of lead(II) chloride?
(Extended) After filtering off a precipitate of barium sulfate, why is it washed with distilled water?
Which compound is insoluble in water?
(Extended) Which is the ionic equation for the formation of a precipitate when silver nitrate solution is added to sodium chloride solution?
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