Written By Riya_I
Last Modified 25-01-2023

Magnesium Hydroxide Formula: Definition, Properties

Magnesium Hydroxide Formula: Magnesium Hydroxide or ‘Milk of Magnesia’ is an inorganic chemical compound with antacid and laxative properties. The chemical formula for Magnesium Hydroxide is \({\text{Mg}}{\left({{\text{OH}}} \right)_2}.\) Magnesium Hydroxide is also an alkaline earth metal hydroxide and naturally occurs as mineral brucite. It has various medicinal uses, and doctors often prescribe a solution of magnesium hydroxide to treat constipation and indigestion.

In this article, students shall learn about the definition, derivation, preparation, properties, and uses of magnesium hydroxide. They can note down all the essential chemical formulas for magnesium hydroxides and use the preparation tricks for the practical exams.

What Is the Chemical Formula for Magnesium Hydroxide? \(\left[{{\text{Mg}}{{\left({{\text{OH}}}\right)}_2}} \right]\)

The chemical formula for magnesium hydroxide is \({\text{Mg}}{\left({{\text{OH}}} \right)_2}.\) It is considered an ionic compound as it contains magnesium \(\left({{\text{M}}{{\text{g}}^{2 + }}} \right)\) and hydroxyl \(\left({{\text{O}}{{\text{H}}^ – }} \right)\) ions.

Magnesium hydroxide can be represented as:

Magnesium Hydroxide molar mass is \(58.3197\,{\text{g}}/{\text{mol}}.\)

Magnesium Hydroxide Formula Derivation

The chemical formula of a compound represents the number of atoms of each element present in one molecule of the compound. The chemical formula of magnesium hydroxide can be derived using the criss-cross method.

In the criss-cross method, if we know the valency of each element of a compound, we can easily write its formula. The symbol of the positive part is written on the left-hand side and the symbol of the negative part on the right. The valency of each element is placed as a subscript on the side of the symbol of another element. Subscript \(1\) is not often written. Using this, the chemical formula of magnesium hydroxide can be derived. That is,

Magnesium hydroxide contains magnesium \(\left({{\text{M}}{{\text{g}}^{2 + }}} \right)\) and hydroxyl \(\left({{\text{O}}{{\text{H}}^ – }} \right)\) radicals. The valency of magnesium is two, and that of hydroxyl radical is one. By crisscrossing the valency numbers and using them as subscripts, we get the formula \({\text{Mg}}{\left({{\text{OH}}} \right)_2}.\) It can be represented as:

Preparation of Magnesium Hydroxide \(\left[{{\text{Mg}}{{\left({{\text{OH}}}\right)}_2}} \right]\)

Magnesium Hydroxide \({\text{Mg}}{\left({{\text{OH}}} \right)_2}\) is found naturally as the mineral brucite.

The preparation of magnesium hydroxide in the laboratory includes the following methods:

1. Magnesium reacts with hot water to form magnesium hydroxide and hydrogen gas. The chemical equation for the reaction can be given as:

\({\rm{Mg}} + \mathop {{{\rm{H}}_2}{\rm{O}}}\limits_{\left( {{\rm{Hot}}} \right)} \to {\rm{Mg}}{\left( {{\rm{OH}}} \right)_2} + {{\rm{H}}_2}\)

2. Magnesium hydroxide is precipitated when the salts of magnesium react with alkaline water. The net ionic equation for such reaction can be given as:

\({\text{M}}{{\text{g}}^{2 + }} + 2{\text{O}}{{\text{H}}^ – } \to {\text{Mg}}{\left({{\text{OH}}} \right)_2}\)

3. Magnesium hydroxide is also produced when magnesium carbonate reacts with sodium hydroxide. The chemical equation for the reaction can be given as:

\({\text{MgC}}{{\text{O}}_3} + 2{\text{NaOH}} \to {\text{Mg}}{\left({{\text{OH}}} \right)_2} + {\text{N}}{{\text{a}}_2}{\text{C}}{{\text{O}}_3}\)

4. The reaction between the aqueous solution of magnesium chloride and sodium hydroxide also gives magnesium hydroxide. The chemical equation for the reaction can be given as:

\({\text{MgC}}{{\text{l}}_2} + 2{\text{NaOH}} \to {\text{Mg}}{\left({{\text{OH}}}\right)_2} + 2{\text{NaCl}}\)

5. The large scale production of magnesium hydroxide involves the treatment of lime \(\left[{{\text{Ca}}{{\left({{\text{OH}}}\right)}_2}} \right]\) with seawater. As a result, magnesium hydroxide precipitates as a solid.

Properties of Magnesium Hydroxide \(\left[{{\text{Mg}}{{\left({{\text{OH}}}\right)}_2}} \right]\)

Let us discuss the physical and chemical properties of magnesium hydroxide.

Physical Properties of Magnesium Hydroxide \(\left[{{\text{Mg}}{{\left({{\text{OH}}}\right)}_2}} \right]\)

Magnesium Hydroxide physical properties include:

Magnesium Hydroxide appears as a white solid. It is an odourless compound.
Magnesium Hydroxide is almost insoluble (very low solubility) in water.
The melting point of Magnesium Hydroxide is approximately equal to \(623\,{\text{K}}.\)
The density of Magnesium Mydroxide is \(2.3446\,{\text{g}}/{\text{c}}{{\text{m}}^3}.\)

Chemical Properties of Magnesium Hydroxide \(\left[{{\text{Mg}}{{\left({{\text{OH}}}\right)}_2}} \right]\)

Magnesium Hydroxide chemical properties include:

Magnesium Hydroxide is less basic in nature. This can be attributed to its low solubility in water.
Magnesium Hydroxide decomposes at higher temperatures to give magnesium oxide and water. The chemical equation for the reaction can be given as:

\({\text{Mg}}{\left({{\text{OH}}} \right)_2}\overset{\Delta }{\mathop \to } {\text{MgO}} + {{\text{H}}_2}{\text{O}}\)

Reactions of Magnesium Hydroxide

Students can learn about what happens when Magnesium Hydroxide reacts with other acids below:

Reaction of Magnesium Hydroxide With Hydrochloric Acid

Magnesium Hydroxide reacts with Hydrochloric Acid to form Magnesium Chloride and water. The chemical equation for the reaction can be given as:

\({\text{Mg}}{\left({{\text{OH}}} \right)_2} + 2{\text{HCl}} \to {\text{MgC}}{{\text{l}}_2} + 2{{\text{H}}_2}{\text{O}}\)

Reaction of Magnesium Hydroxide With Sulphuric Acid

Magnesium Hydroxide reacts with Sulphuric Acid to form Magnesium Sulphate and water. The chemical equation for the reaction can be given as:

\({\text{Mg}}{\left({{\text{OH}}} \right)_2} + {{\text{H}}_2}{\text{S}}{{\text{O}}_4} \to {\text{MgS}}{{\text{O}}_4} + 2{{\text{H}}_2}{\text{O}}\)

Reaction of Magnesium Hydroxide With Acetic Acid

Magnesium Hydroxide reacts with Acetic Acid to give Magnesium Acetate and water. The chemical equation for the reaction can be given as:

\(2{\text{C}}{{\text{H}}_3}{\text{COOH}} + {\text{Mg}}{\left({{\text{OH}}} \right)_2} \to {\text{Mg}}{\left({{\text{C}}{{\text{H}}_3}{\text{COO}}} \right)_2} + 2{{\text{H}}_2}{\text{O}}\)

The above reactions are examples of neutralisation reactions.

Uses of Magnesium Hydroxide \(\left[{{\text{Mg}}{{\left({{\text{OH}}}\right)}_2}} \right]\)

Magnesium Hydroxide has got many uses. They include:

A suspension of Magnesium Hydroxide called Milk of Magnesia is widely used as an antacid. As an antacid, magnesium hydroxide works by neutralising the hydrochloric acid present in the stomach and releasing water.
It is used as a laxative (the substance used to improve bowel movements and loosen the stool).
Magnesium hydroxide is used as a food additive. It is known as a safe food additive by the FDA.
Magnesium hydroxide is also used as an antiperspirant.
Acidic wastewater can be neutralised by adding magnesium hydroxide. Therefore, it is used in water treatment.
Brucite, the naturally occurring mineral of magnesium hydroxide, is widely used as a fire retardant.
In the cosmetic industry, magnesium hydroxide is used as a \({\text{pH}}\) controlling agent.
It is also used as a fuel additive to treat heavy oil fuels and crude oil.

Summary

Magnesium Hydroxide is an alkaline earth metal hydroxide. Its chemical formula is \({{\rm{Mg}}{{\left( {{\rm{OH}}} \right)}_2}}.\) It is commonly used as an antacid in the form of ‘milk of magnesia’. It is odourless and appears as a white solid. It naturally occurs as brucite. It can be prepared in the laboratory using different methods, which are explained in this article. We have also explained the properties and different uses of magnesium hydroxide.

FAQs on Magnesium Hydroxide

Q.1. Calculate the formula unit mass of Magnesium Hydroxide.
Ans: The formula unit mass is the sum of the atomic masses of all the atoms that are present in one formula unit of the given compound. Therefore, the formula unit mass of magnesium hydroxide can be found as.
The atomic mass of magnesium \( = 24.305\,{\text{u}}\)
The atomic mass of Oxygen \( = 15.999\,{\text{u}}\)
The atomic mass of hydrogen \( = 1.007\,{\text{u}}\)
The formula unit mass of magnesium hydroxide \(\left[{{\text{Mg}}{{\left({{\text{OH}}} \right)}_2}} \right] = \left({1 \times 24.305}\right) + \left({2 \times 15.999} \right) + \left({2 \times 1.007} \right) = 58.317\,{\text{u}}.\)

Q.2. What is the formula for Magnesium Hydroxide?
Ans: Magnesium hydroxide is an inorganic compound with the chemical formula \({\text{Mg}}{\left( {{\text{OH}}} \right)_2}.\) It is an alkaline earth metal hydroxide.

Q.3. What is Magnesium Hydroxide used for?
Ans: There are many uses of magnesium hydroxide. It is commonly used as an antacid in the form of milk of magnesia. Other uses include its use as a laxative, food additive, \({\text{pH}}\) controlling agent, etc.

Q.4. What are the common side effects of Magnesium Hydroxide?
Ans: The common side effects of magnesium hydroxide include vomiting, severe nausea, diarrhoea, etc.

Q.5. How does Magnesium Hydroxide cure an upset stomach?
Ans: A stomach becomes upset due to increased acidity. Therefore, when magnesium hydroxide is used, it will neutralise the acid in the stomach. That is, magnesium hydroxide works by neutralising the hydrochloric acid present in the stomach and by releasing water.

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