Milk of Magnesia is an over-the-counter medicine for upset stomachs. The chemical name is magnesium hydroxide with the formula Mg(OH)2. This is the first example of a classical Arrhenius base, a base that gives off an OH- anion directly from its molecule. The excess OH- anions given off by Mg(OH)2 as shown in equation in the picture is what makes the solution basic with a pH of 10. Magnesium hydroxide is a weak base as represented by the double arrow that means not all the molecules on the left side of the double arrows separate 100% into ions.