6D.1 Precipitation Reactions
A precipitation reaction occurs when two or more soluble species combine to form
an insoluble product that we call a precipitate. The most common precipitation reaction
is a metathesis reaction, in which two soluble ionic compounds exchange
parts. When a solution of lead nitrate is added to a solution of potassium chloride,
for example, a precipitate of lead chloride forms. We usually write the balanced reaction
as a net ionic equation, in which only the precipitate and those ions involved
in the reaction are included. Thus, the precipitation of PbCl2 is written as