Magnesium oxide (MgO), also known as periclase, is a chemical compound of magnesium and oxygen. It is an ionic compound with the magnesium ion (Mg2+) and the oxide ion (O2-) held together by strong electrostatic forces. This article delves into the reasons why MgO is insoluble in water, examining its molecular structure, ionic bonding, and the role of hydration energy in its dissolution process.

Ionic Bonding and Strong Electrostatic Forces

MgO is an ionic compound, meaning that it is composed of positively charged ions (cations) and negatively charged ions (anions). In this case, the magnesium ion (Mg2+) and the oxide ion (O2-) are held together by strong electrostatic forces. These forces are responsible for the high lattice energy of MgO, which is the energy required to separate the ions from each other. The strong lattice energy makes it difficult for water molecules to break apart the ionic bonds and dissolve the compound. Unlike covalent compounds, where molecules are held together by weaker van der Waals forces, ionic compounds like MgO possess much stronger electrostatic attractions between their ions. This difference in bonding strength significantly influences their solubility in water.

Hydration Energy and Dissolution

When an ionic compound dissolves in water, it undergoes a process called hydration. During hydration, water molecules surround the ions and interact with them through electrostatic forces. The energy released during this interaction is known as hydration energy. For a compound to dissolve in water, the hydration energy must be greater than the lattice energy. In the case of MgO, the lattice energy is much higher than the hydration energy. This means that the energy required to break apart the ionic bonds is greater than the energy released when the ions are surrounded by water molecules. Consequently, MgO remains insoluble in water.

Limited Solvation of Ions

The insolubility of MgO in water can also be attributed to the limited solvation of its ions. Solvation refers to the process by which ions are surrounded by water molecules. The extent of solvation depends on the charge and size of the ion. Smaller and highly charged ions, such as Mg2+, are less solvated by water molecules compared to larger, less charged ions. This limited solvation further hinders the dissolution of MgO in water.

The Role of Temperature and Pressure

Temperature and pressure can influence the solubility of MgO in water to some extent. Increasing the temperature generally increases the solubility of most substances, including ionic compounds. This is because higher temperatures provide more energy to overcome the lattice energy and promote hydration. However, the effect of temperature on the solubility of MgO is relatively small. Similarly, increasing pressure can also increase the solubility of MgO, but the effect is typically not significant.

Applications of Insoluble MgO

Despite its insolubility in water, MgO has various industrial and commercial applications. Its refractory properties, high melting point, and resistance to chemical attack make it suitable for use in crucibles, furnace linings, and as a component in cements and refractory bricks. Additionally, MgO is employed as a catalyst in various chemical reactions, an abrasive in polishing compounds, and an additive in fertilizers and animal feed.


In conclusion, MgO's insolubility in water is primarily due to its strong ionic bonding, high lattice energy, and limited solvation of its ions. These factors collectively prevent the dissolution of MgO in water. While temperature and pressure can influence its solubility to a certain extent, their effects are typically modest. Despite its insolubility, MgO finds applications in various industries and sectors, leveraging its unique properties and chemical stability.

Frequently Asked Questions

1. Can MgO be dissolved in acidic or basic solutions?

MgO is slightly soluble in acidic solutions due to the formation of soluble magnesium salts. However, it is virtually insoluble in basic solutions because the hydroxide ions (OH-) compete with water molecules for solvating the magnesium ions.

2. What are some common applications of insoluble MgO?

Insoluble MgO is commonly used in refractory materials, crucibles, furnace linings, cements, and fertilizers. It is also employed as a catalyst, abrasive, and additive in animal feed.

3. How does the lattice energy of MgO compare to other ionic compounds?

The lattice energy of MgO is relatively high compared to many other ionic compounds. This is due to the strong electrostatic forces between the small, highly charged magnesium and oxide ions.

4. Can MgO be converted into a soluble form?

Yes, MgO can be converted into a soluble form by reacting it with acids to form soluble magnesium salts. For example, reacting MgO with hydrochloric acid (HCl) produces magnesium chloride (MgCl2), which is soluble in water.

5. What are some potential environmental implications of MgO insolubility?

The insolubility of MgO can have environmental implications, particularly in areas where it is used extensively. For instance, the disposal of MgO-containing industrial waste can lead to the accumulation of this compound in the environment, potentially affecting soil and water quality.



Leave a Reply

Ваша e-mail адреса не оприлюднюватиметься. Обов’язкові поля позначені *

Please type the characters of this captcha image in the input box

Please type the characters of this captcha image in the input box

Please type the characters of this captcha image in the input box

Please type the characters of this captcha image in the input box