The common ion effect is the decreased solubility of the ionic precipitate in the solution. To promote the precipitation of the calcium sulfate, magnesium sulfate must be added.
It is a phenomenon that is due to the addition of the common ion already present in the solution that affects the equilibrium and is used to decrease the solubility of the solute present in the solution to increase the precipitation rate.
Magnesium sulfate will be added to the solution as it already contains the sulfate ion in the form of calcium sulfate. This will increase the precipitation of the compound as the common ion added will decrease the solubility.
Therefore, magnesium sulfate will be added to promote precipitation.
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