1. Will a precipitate form when two solutions are mixed?
The common ion effect
Will a precipitate form when two solutions are mixed?

2. Worked example
25 cm3 0f mol dm-3 potassium chromate ( KCrO4) are mixed with 75 cm3 of mol dm-3 lead (II) nitrate. Will a precipitate of lead chromate form?
[ ksp lead(II) chromate = 1.8 x 10-14mol2 dm6]

3. Step 1 Determine the ionic equation
PbCrO4 (s) = Pb2+ (aq) CrO4 2- (aq)
ksp = [ Pb2+ ] [ CrO4 2- ]

4. Step 2 Determine the initial concentrations of each ion when mixed
[ CrO4 2- ] = 25/100 x mol dm-3
= mol dm-3

5. Step 3 Similarly work out the concentration of the Pb2+(aq)
Answer = mol dm-3

6. Step 4 Multiply the two values from steps 2 and 3
Answer = 4.69 x 10-8
Ask : Is this greater than the numerical value for ksp ?
Yes means a precipitate will form !