Question

What type of reaction leads to the formation of a precipitate?

Answer 1

Typically, we examine a `"solubility equilibrium....."`

Explanation:

Typically, we examine a solubility equilibrium, where concentrations of (metal) cation, and (non-metal) anion occur such that their product exceeds a given constant, i.e. `K_"sp"`.

And we can take one hallowed example......

`Ag^+ +Cl^(-) rightleftharpoonsAgCl(s)darr`

For standard conditions, a `K_"sp"` value can be measured such that.....

`K_"sp"=[Ag^+][Cl^-]=1.77xx10^-10`

And if the product `[Ag^+][Cl^-]>=1.77xx10^-10`, then precipitation WILL occur.

See here and links for further detail....

For standard reactions in the inorganic laboratory, we use general rules to assess aqueous solubility: all the salts of the alkali metals are soluble; all the nitrates are soluble; all halides are soluble except for `AgX`, `Hg_2X_2`, `PbX_2`.......; all sulfides and phosphates and hydroxides are insoluble......; all hydroxides are insoluble.....etc. etc.