When 1.00 g. of MgCO3 is added to 2.0 L of water, some, but not all, will dissolve to form a saturated solution. Calculate the mass of solid that remains undissolved.

Answer 1

........MgCO3 ==> Mg^2+ + CO3^2-
I.......solid.....0........0
C...x dissolves...x........x
E.......solid......x.......x

Ksp = (Mg^2+)(CO3^2-)
Substitute for Ksp and the E line from the ICE chart and solve for x = solubility MgCO3 in mols/L.
You have 2L therefore, the solubility will be ?mols/L x 2L = ? then convert that to grams by g = mols x molar mass.
Subtract from 1.00g to find the amount not dissolved.