Deciding whether a precipitate will form

We can cause a sparingly soluble salt to precipitate out of solution if the product of the concentration of the ions concerned exceeds the K_sp.

Say I have 50.0cm³ of 0.050 mol dm^-3 silver nitrate and 50.0cm³ of 0.010 mol dm^-3 potassium bromate, and I pour one solution into the other. Given that the solubility product of silver bromate is 6.0 x 10^-5 mol² dm^-6, will the solid precipitate out?

1. Determine the [Ag⁺_(aq)] and the [BrO₃^–_(aq)] in the mixed solution.

2. Work out the total ion concentration in the mixture and compare against the K_sp.

Practice questions

Show by calculation whether a precipitate will form when 30cm³ of each of the following solutions are mixed:

(a) 1.0 x 10^-3 mol dm^-3 of silver nitrate and 1.0 x 10^-3 mol dm^-3 sodium chloride

(b) 1.3 x 10^-3 mol dm^-3 of lead(II) nitrate and 1.0 x 10^-3 mol dm^-3 potassium bromide 

Salt	Solubility product
AgCl	2.0 x 10-10  mol2 dm-6
PbBr2	3.9 x 10-5 mol3 dm-9

Answers