Chemistry / Unit 3 Chem 0437 worked example, 60 to 90 seconds
Predicting Precipitation Reactions
The idea
Predicting a precipitation reaction means combining two solutions' ions in every possible new pairing, then checking each pairing against solubility rules for an insoluble product.
In practice
Mixing solutions of potassium chloride and silver nitrate offers two possible new pairings: potassium with nitrate, and silver with chloride. Solubility rules mark all common nitrate salts and most potassium salts as soluble, but rule silver chloride insoluble. A precipitate of AgCl is therefore predicted to form, while potassium and nitrate ions remain dissolved in solution as spectators, giving the net ionic equation Ag+ + Cl− → AgCl(s), the same result any silver-and-chloride pairing would produce.
Where people slip
Checking only the original pairing of ions, potassium with chloride and silver with nitrate, misses the actual new pairing that solubility rules flag as insoluble.
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