The values of Ksp of CaCO3 and CaC2O4 are 4.7×10-9 and 1.3×10-9respectively at 25oC. If the mixture of these two is washed with water, what is the concentration of Ca2+ ions in water?

CaCO3⟶Ca2++CO32- CaC2O4⟶Ca2+x+C2O42-x Now, Ca2+=x+y  and x(x+y)=4.7×10-9                       .............(i) y(x+y)=1.3×10-9                             ..............(ii)  Dividing equation (i) and (ii) we get  xy=3.6 ∴ x=3.6y  Putting this value in equation (ii), we get  y(3.6y+y)=1.3×10-9  On solving, we get y=1.6×10-5  and x=3.6×1.6×10-5=5.76×10-5 ∴Ca2+=(x+y)=1.6×10-5+5.76×10-5 ∴ Ca2+=7.46×10-5M