What is the Difference Between Magnesium Oxide and Magnesium Hydroxide?

Magnesium oxide (MgO) and magnesium hydroxide (Mg(OH)₂) are both magnesium compounds, but they have different chemical structures and properties. The key differences between them are:

1. Chemical Formula: Magnesium oxide has the chemical formula MgO, while magnesium hydroxide has the chemical formula Mg(OH)₂.
2. Hydroxide Anions: Magnesium oxide has one oxygen anion per one magnesium cation, whereas magnesium hydroxide has two hydroxide anions per one magnesium cation.
3. Solubility: Magnesium oxide is hygroscopic, meaning it is highly water-soluble. In contrast, magnesium hydroxide is poorly water-soluble.
4. Reactivity: The reactivity of magnesium oxide particles is typically lower than that of magnesium hydroxide, requiring a higher dose to achieve the same pH or alkalinity increase.
5. Magnesium Oxide Sources: Magnesium oxide is typically obtained from the calcination (heating) of magnesite ore.
6. Magnesium Hydroxide Sources: Magnesium hydroxide is most regularly obtained as a liquid, although it can be a solid if not mixed with water. It is often found in the pharmacy as a liquid and, when mixed with water, is called milk of magnesia.

Both compounds are used in various applications, such as treating acid stomach, indigestion, and constipation. However, due to their differences in solubility and reactivity, they may not be interchangeable in all situations.

Comparative Table: Magnesium Oxide vs Magnesium Hydroxide

Here is a table detailing the differences between magnesium oxide and magnesium hydroxide:

Magnesium oxide has the chemical formula MgO and is a white, hygroscopic solid mineral. In the presence of water, magnesium oxide converts into magnesium hydroxide. Magnesium hydroxide has the chemical formula Mg(OH)2 and is a weak base. It is commonly used to relieve symptoms of acid stomach and to help relieve constipation. Magnesium oxide is highly water soluble, while magnesium hydroxide is soluble in water.