Answer to Question #107580 in Inorganic Chemistry for Valerie Gerlach

Question

The magnesium and calcium ions present in seawater can be seperated by selective precipitation by adding a reagent that will cause one to precipitate while the other stays in solution. Mg=.035 M and Ca=.020M
Using a table of Ksp values, find two anions that could be used to seperate the ions and explain why?

Answer 1

Solubility product constant is simplified equilibrium constant defined for equilibrium between a solids and its respective ions in a solution. Its value indicates the degree to which a compound dissociates in water. The higher the solubility product constant, the more soluble the compound.

When two anions form slightly soluble compounds with the same cation, or when two cations form slightly soluble compounds with the same anion, the less soluble compound (usually, the compound with the smaller K_sp) generally precipitates first when we add a precipitating agent to a solution containing both anions.