Question

What is the minimum concentration of sulfate ion, SO4 2- that must be present in a 0.050 M solution of Ca2+ to cause a precipitate to form? The K sp for calcium sulfate, CaSO4, is 7.10 × 10-5

Answer 1

Answer:

[$SO_4^{-2}$ ]minimum=1.42*$10^{-3}$M

Explanation:

Precipitate occurs only when the ionic product is greater than the solubility product.

I.e. Kip>Ksp  

And from above equation it is clearly that the minimum value of Kip is equal to Ksp

$CaSO_4$ (aq)  = $Ca^{+2}$ (aq)+$SO^{-2}$ (aq);

Ksp=[$Ca^{+2}$][$SO_4^{-2}$];

Hence Kip=Ksp; minimum value of Kip is equal to Ksp and this will give the minimum concentration of SO4-2 to precipitate the 0.050 M solution of Ca2+

Kip = [$Ca^{+2}$][$SO_4^{-2}$]  = Ksp=7.10 × 10-5

[$SO_4^{-2}$]  =Ksp/[$Ca^{+2}$] ;

[$SO_4^{-2}$]=(7.10 × 10-5)/0.050;

[$SO_4^{-2}$]minimum=1.42*$10^{-3}$ M