As compounds formed by the alkali earth metals are predominately ionic, their solubility generally depends on the difference in charge between the two ions and to water.
If the attaction between the two ions is stronger than their attraction to water, the compound is insoluble.
If the attraction between an ion and water is stronger than with the other ion, the compound is soluble.
Solubility of sulphates decreases down the group. When sulphuric acid/sodium sulphate is added...
MgSO4 = soluble no precipitate
BeSO4 = soluble no precipitate
CaSO4 = sparingly soluble faint white precipitate
SrSO4 = insoluble white precipitate
BaSO4 = insoluble thick white precipitate
(BaSO4 used as a "barium meal" as it is good at absorbing X-rays so highlights the gut easily after consumption.)
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