Passage IV

Barium (Ba), calcium (Ca), magnesium (Mg), and strontium (Sr) exist in their compounds as M²⁺ ions (Mg²⁺, Ca²⁺, etc.). When solutions of these ions are mixed with solutions containing X^2- ions (SO₄^2- [sulfate], CO₃^2- [carbonate], etc.), salts will precipitate (form a solid) if the combination of positive and negative ions forms an insoluble (not dissolving in solution) salt, MX:

M²⁺ (solution) + X^2- (solution) → MX (solid)

The following table summarizes the results of combining various metal nitrate solutions of equal concentrations with various solutions containing X^2- ions.