Question

find the molar solubility of bacro4 in pure water

Answer 1

let x = mol/L of BaCrO4 that dissolve : this will give x mol/L Ba2+ and x mol/L CrO42- 
Kas = [Ba2+][CrO42-] = (x)(x) = 2.1 x 10^-10 
x = molar solubility = 1.4 x 10^-5 M