Question

Does the ionic strength of saturated CaSO₄ solution in de-ionized water have a significant impact on its solubility? What does this imply on an atomic scale about the interactions between Ca²⁺ and SO₄^2- ions in the solution?

Answer 1

ionic strength is typically a measure of the concentration of ions in a solution ,,with the ions of higher charge being more counted as they impart more electrostatic attractions with ions of opposite charges.

I=Ionic strength=Ci*zi^2 ,Zi=charge of species i,ci=concentration of ionic species i

Also ,activity =ai=ci*i

i=mean ionic activity

Solubility of an electrolyte can be accounted for by using their solubility product or Ksp which is the measure of the product of activity of ions in solution

For any electrolyte,

A_mB_n <--->mAⁿ⁺ +nB^m-

^Ksp=a(Aⁿ⁺)^m* a(B^{m-_)^n}

^_For CaSO_{4,Ksp=a(Ca2+) * a(SO42-)=(+)[Ca²⁺] * (-)[SO4^2-]}

_{So, Ksp varies inversely as or mean ionic activity of ions,=+ *-}

_{And, Ksp varies directly as Ci or concentration of ions}

_{Thus,Ksp or solubility varies directly as Ionic strength.It increases with ionic strength.}

_{On atomic scale ,it can be incurred that ions with higher solubility ,have more ions in solutions so the electrostatic interactions between ions is more,giving higher measure of ionic strength.}