Precipitation reactions
A precipitation reaction is one in which substances in solution are mixed and an insoluble product is made. The insoluble product is called a An insoluble solid formed by a reaction. and can be seen as a solid forming in the reaction mixture.
Precipitation reaction of lead nitrate and potassium iodide
Below is an example of a precipitation reaction. Notice the two aqueous solutions make a solid substance.
\(AgNO_{3}(aq) + NaCl(aq)\rightarrow AgCl(s) + NaNO_{3}(aq)\)
If state symbols are not given you need to use the solubility tables called "Solubilities of Selected Compounds in Water" in the SQA Data Booklet to find if an insoluble product is made.
Precipitation reactions can be used in qualitative analysis for example silver nitrate is often used to test for halide (group 7) ions. The limewater test for carbon dioxide is also a qualitative analysis based on a precipitation reaction. Limewater is a solution of calcium hydroxide and the precipitate is calcium carbonate.
\(Ca(OH)_{2(aq)} + CO_{2(g)} \rightarrow CaCO_{3(s)} + H_{2}O_{(l)}\)
Combining two soluble salts causes a precipitation reaction
