Why Is Milk of Magnesia an Antacid

Magnesium-containing compounds are often common everyday medicines. What makes milk of magnesia an effective antacid  

In pharmacology, the term milk refers to an aqueous suspension of a water-insoluble drug. The antacid milk of magnesia contains a saturated solution of the salt magnesium hydroxide. Magnesium hydroxide does not dissolve readily in water, and a saturated solution of this substance simply means that so much 

The solubility S of magnesium hydroxide (in units of moles per liter) can be computed from the equilibrium constant (the solubility product) for the dissolution of the salt. For S equal to the moles per liter of Mg(OH)2 dissolved  

With a molecular weight for magnesium hydroxide of 58.3 g/mole, the solubility is equivalent to 8.36 mg per liter. The Bayer product Original Phillips Milk of Magnesia contains 400 mg of magnesium hydroxide per teaspoon (volume estimated at 5 mL) or 8.00 x 104 mg per liter. Clearly a saturated solution From the amount of dissolved Mg(OH)2, the pH of the solution can be determined, for 

The alkaline nature of the saturated Mg(OH)2 solution provides the antacid capabilities of this over-the-counter medicine. 

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