13. Precipitation & Solubility

Mix two clear solutions and a solid can suddenly appear. That solid is a precipitate.

[missing figure: chem_precipitation]

A precipitation reaction is a double replacement in which one of the new pairings turns out to be insoluble — it cannot stay dissolved, so it drops out of solution as a solid.

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

Read the state symbols to spot it: everything starts as (aq), and one product is (s). That (s) is the precipitate.

A substance is soluble if it dissolves in water and insoluble if it doesn't. Cloudiness appearing in a clear liquid is one of the classic signs of a chemical reaction.

⚠️ Common misconception: a precipitate is not the same as a substance simply settling or freezing. It is a new compound made by the reaction.

💡 Tip: look for (aq) + (aq) → (s) + (aq). The (s) is your precipitate.