Precipitation Reactions
Mixing solutions can form an insoluble solid.
About this topic
A precipitation reaction occurs when two aqueous solutions are mixed and form an insoluble solid, the precipitate. Solubility rules predict the outcome: nitrates, group 1 salts and ammonium salts are soluble; most chlorides are soluble except silver, lead and mercury(I); most carbonates, phosphates and hydroxides are insoluble.
The cations and anions swap partners, and if one new combination is insoluble it falls out of solution. For example, silver nitrate and sodium chloride: AgNO3(aq) + NaCl(aq) gives AgCl(s) + NaNO3(aq). The white solid silver chloride appears at once. The ions that stay in solution and do not take part are spectator ions, which we remove when writing the net ionic equation: Ag+(aq) + Cl-(aq) gives AgCl(s).
Example: adding potassium iodide to lead(II) nitrate produces a brilliant yellow precipitate of lead(II) iodide, a classic demonstration known as golden rain when it is heated and cooled. Precipitation is used to test for ions in water analysis, to remove metals and phosphates in wastewater treatment, and in forming kidney stones and stalactites.
A frequent misconception is that all reactions of two solutions give a precipitate. If every possible product is soluble, no reaction occurs, and you only have a mixture of ions. Learn the solubility rules in order of priority.
Key ideas
- Use solubility rules
- Net ionic equations drop spectator ions
- Silver chloride precipitates
Quick check
Use cases: where Precipitation Reactions helps
- Homework: review the key idea behind Precipitation Reactions before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Precipitation Reactions without notes.
- Visual learning: play with the interactive lab to see how Precipitation Reactions changes when you adjust its inputs.
- Teaching a friend: explain Precipitation Reactions in your own words, then compare your version with the key ideas.
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Frequently asked questions
What is Precipitation Reactions?
Mixing solutions can form an insoluble solid.
What will I learn in Precipitation Reactions?
Use solubility rules. Net ionic equations drop spectator ions. Silver chloride precipitates.
Is Precipitation Reactions part of Chemistry?
Yes. It is one of 150 Chemistry topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Precipitation Reactions lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study Precipitation Reactions?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.