Trends in Solubility of the Hydroxides

Magnesium hydroxide has very low solubility in water.Calcium hydroxide is only slightly soluble in water. The product is called limewater and is used as a test for carbon dioxide.The solubility of group 2 hydroxides increases down the group.
Magnesium hydroxide is only very slightly soluble in water, giving a pH of about 10. Barium hydroxide is much more soluble with a pH of about 13.

Milk of Magnesia

Milk of Magnesia is a saturated solution of magnesium hydroxide mixed with solid magnesium hydroxide. It acts as an antacid neutralising the HCl in the stomach to relieve the symptoms of indigestion. The low solubility of magnesium hydroxide means there is a low concentration of OH^- ions which poses no risk to health.: Mg(OH)₂ (s) + 2HCl (aq) → MgCl₂ (aq) + 2H₂O (l)