Question

Magnesium carbonate, mgco3, has a ksp value of 6.80×10−6 . what happens when magnesium and carbonate solutions are mixed to give 2.50×10−3 m mg2+ and 2.00×10−3 m co32−?

Answer 1

when MgCO₃ dissolves it dissociates into the following ions
MgCO₃ ---> Mg²⁺ + CO₃²⁻
reaction quotient (Q) = [Mg²⁺][CO₃²⁻]
ksp is the solubility product constant. If the reaction quotient > ksp the ion will precipitate, however if Q< ksp the salt will not precipitate.
First we need to calculate Q
Q = (2.5 x 10⁻³ M)(2.0 x 10⁻³ M)
Q = 5 x 10⁻⁶
ksp of salt is 6.8 x 10⁻⁶
however Q < ksp therefore salt will not precipitate.