Question

The values of ksp of caco3 and cac2o4 are 4.7 × 10–9 and 1.3 × 10–9 respectively at 25°c. If the mixture of these two is washed with water, what is the concentration of ca2 ions in water

Answer 1

First of all we calculate the concentration of Ca+2 in these salts

CaCO3:

$Ksp=[Ca+2][CO-3]\\Since both ions have same concentration hence\\</p><p>Ksp=[ca+2]^{2}\\ </p><p>and\\</p><p>4.7× 10-9=[ca+2]^{2}\\\</p><p>sqrt{4.7× 10-9} =[ca+2]\\</p><p>[ca+2]=2.16× 10-3$..............................1

Now CaC2O4:

$Ksp=[Ca+2][C2O4-2]\\Since both ions have same concentration hence\\</p><p>Ksp=[ca+2]^{2}\\ </p><p>and\\</p><p>1.3× 10-9=[ca+2]^{2}\\\</p><p>sqrt{1.3× 10-9} =[ca+2]\\</p><p>[ca+2]=1.14× 10-3$............................2

The total no. of Calcium ions in solution will be the sum of 1 and 2

2.16×10-3+1.14×10-3=3.40×10-3