Reactions of Group 2 Oxides

Group 2 oxides react with water and release hydroxide ions to form alkaline solutions.CaO(s) + H₂O(l) → Ca(OH)₂(aq)Group 2 hydroxides are only slightly soluble in water so form a solid precipitate when the solution becomes saturated.For any Group 2 oxide MO the equation is:MO(s) + H₂O(l) → M(OH)₂(aq)The oxide ion reacts with water to release hydroxide ions:O^2- + H₂O → 2OH^-Because they form alkalis, Group 2 oxides are basic oxides. The resulting solutions are colourless.The solubility of the Group 2 hydroxides increases down the group. Magnesium hydroxide is only slightly soluble in water, so few OH^- ions are released and the solution has a pH of about 10. Barium hydroxide is much more soluble, so more OH^- ions are released and the pH is about 13. The pH of these alkaline solutions therefore increases down the group, from about 10 to about 13.This basic nature is useful: farmers spread calcium hydroxide on fields to raise the pH of acidic soils.