Difference Between Magnesium Oxide and Magnesium Hydroxide

The key difference between magnesium oxide and magnesium hydroxide is that magnesium oxide has an oxide anion per one magnesium cation, whereas magnesium hydroxide has two hydroxide anions per one magnesium cation.

Thus, the basic difference between magnesium oxide and magnesium hydroxide is the chemical structures of these two compounds. The chemical formula of magnesium oxide is MgO while the chemical formula of magnesium hydroxide is Mg(OH)₂.

CONTENTS

1. Overview and Key Difference
2. What is Magnesium Oxide 
3. What is Magnesium Hydroxide
4. Side by Side Comparison – Magnesium Oxide vs Magnesium Hydroxide in Tabular Form
5. Summary

What is Magnesium Oxide?

Magnesium oxide is the compound having the chemical formula MgO. It is a white, hygroscopic solid mineral. It is very important as a source of magnesium. Although the empirical formula of this compound is MgO, it actually occurs as a lattice which has magnesium cations and oxide anions held together by ionic bonds. In the presence of water, magnesium oxide converts into magnesium hydroxide. Moreover, we can reverse this reaction by heating the compound to remove the moisture.

We can produce this compound via the calcination of magnesium carbonate. Further, if we calcine the magnesium carbonate at different temperatures, it will give magnesium oxide with different reactivity. For example, if we use high temperatures (around 1500 – 2000 °C), it gives an unreactive form which can be used as a refractory.

When considering the applications of magnesium oxide, it is mainly useful as a refractory material, important as a principal ingredient in many construction materials, i.e. as a major component in Portland cement, as a food additive, as a reference for the white colour in colourimetry, etc.

What is Magnesium Hydroxide?

Magnesium hydroxide is the chemical compound having chemical formula Mg(OH)2. It is a white solid, but unlike magnesium oxide, this compound is not hygroscopic because it has low water solubility. It occurs in nature as the mineral brucite.

We can produce this compound easily by adding water to magnesium oxide. Or else, we can produce it by combining a solution of magnesium salts with alkaline water. Thus, this reaction gives a precipitate of magnesium hydroxide. However, in commercial scale, we produce this material via treating sea water with lime. And, this reaction gives tons of magnesium hydroxide.

When considering the uses of this compound, it is mainly important as the precursor for the production of magnesium oxide. Moreover, in its suspension form, this material is important as either an antacid or as a laxative. Also, it is useful as a food additive. Other than that, this material is important to neutralize acidic waste water.

What is the Difference Between Magnesium Oxide and Magnesium Hydroxide?

Magnesium oxide is the compound having the chemical formula MgO, while Magnesium hydroxide is the chemical compound having chemical formula Mg(OH)₂. The key difference between magnesium oxide and magnesium hydroxide is that magnesium oxide has an oxide anion per magnesium cation, whereas magnesium hydroxide has two hydroxide anions per one magnesium cation.

Furthermore, magnesium oxide is hygroscopic, but magnesium hydroxide is not hygroscopic. That means; magnesium oxide is highly water soluble, but magnesium hydroxide is poorly water soluble.

The below infographic presents more comparisons related to the difference between magnesium oxide and magnesium hydroxide.

Summary – Magnesium Oxide vs Magnesium Hydroxide

Magnesium oxide is the compound having the chemical formula MgO while Magnesium hydroxide is the chemical compound having chemical formula Mg(OH)₂. In summary, the key difference between magnesium oxide and magnesium hydroxide is that magnesium oxide has an oxide anion per magnesium cation, whereas magnesium hydroxide has two hydroxide anions per one magnesium cation.

Reference:

1. “Magnesium Oxide.” Wikipedia, Wikimedia Foundation, 20 May 2019, Available here.

Image Courtesy:

1. “Magnesium oxide” By – Walkerma assumed (based on copyright claims). – No machine-readable source provided. Own work assumed (based on copyright claims) (Public Domain) via Commons Wikimedia
2. “Hydroxid hořečnatý” By Ondřej Mangl – Vlastní sbírka (Public Domain) via Commons Wikimedia