A 50.0 - mL sample of 1.50*10-2 M Na2SO4 (aq) is added to 50.0 mL of 1.28*10-2 M Ca (NO3) 2 (aq). What percentage of the Ca2 + remains unprecipitated?

When we have Ksp CaSO4 = 9.1x10^-6 so by substitution in Ksp formula:

Ksp CaSO4 = [Ca+2][SO4]

1.9x10^-6 = [Ca+2][1.5x10^-2]

∴ [Ca+2] M in the solution = 1.27x10^-4

when percent remaining = [Ca in solution]/[C original value] * 100

= [ (1.27x10^-4 * (50ml+50ml) ]/[1.28x10^-2*50ml]*100

≈ 2%