What is a precipitation reaction?

A precipitation reaction occurs when two soluble ionic solutions are mixed and an insoluble solid a precipitate forms.

Example: AgNO₃(aq) + NaCl(aq) → AgCl(s)↓ + NaNO₃(aq)

• Precipitates are identified by colour: AgCl (white), PbS (black), BaSO₄ (white).
• Used in qualitative analysis to identify ions in solution.