Dihydrogen: While everyone knows about Hydrogen – the first element on the atomic table and one of the most abundant elements on Earth. However, Hydrogen is rarely found in its original form since it is very reactive and unstable in nature. However, if it combines with another atom of Hydrogen, it becomes Dihydrogen (\({{\rm{H}}_2}\)).

This molecular form of Hydrogen known as Dihydrogen is the most common form of Hydrogen on Earth since it is a very stable gas. Interestingly, a dihydrogen molecule is the smallest molecule on the planet. In this article, we will study the molecule of hydrogen- Dihydrogen and its properties and applications.

What is Dihydrogen?

Dihydrogen is the diatomic molecule formed from two hydrogen atoms by a covalent bond, fulfilling each of their required duplet stable configurations. Although hydrogen is the lightest atom, dihydrogen is the lightest known molecule. The atomic weight of the hydrogen atom is \(1.008\,{\rm{amu}}\) and the molecular weight of the dihydrogen molecule is \(2.016\,{\rm{amu}}\).

Under standard conditions for temperature and pressure, dihydrogen exists as a colourless, tasteless, and odourless combustible gas.

Occurrence of Dihydrogen

Dihydrogen in its state is found in the sun, and most of the stars and the planet Jupiter is composed mostly of hydrogen. On Earth, it occurs in tiny quantities in volcanic gases.

Structure of Dihydrogen

Dihydrogen occurs as a molecule in nature as \({{\rm{H}}_2}\), having a single covalent bond between hydrogen atoms. While doing so, the duet electronic configuration of both the atoms is satisfied. Thus, this molecule has a linear shape and is non-polar.

Preparation of Dihydrogen

The principal sources of Hydrogen on Earth are water, acids, and alkalis. These compounds liberate hydrogen gas when they react chemically.

1. By Active Metals

When dilute hydrochloric acid or dilute sulphuric acid reacts with metals placed above hydrogen in the activity series, hydrogen gas is liberated. Active metals like magnesium, zinc, iron etc., react with dilute hydrochloric acid or dilute sulphuric acid to liberate hydrogen gas.

The reaction of metals with dilute \({\rm{HCl}}\)	The reaction of metals with dilute \({{\rm{H}}_2}{\rm{S}}{{\rm{O}}_4}\)
\({\rm{Mg}}\,{\rm{ + }}\,{\rm{2HCl}}\, \to {\rm{MgC}}{{\rm{l}}_{\rm{2}}}{\rm{ + }}{{\rm{H}}_{\rm{2}}}\) \({\rm{Zn}}\,{\rm{ + 2HCl}} \to {\rm{ZnC}}{{\rm{l}}_{\rm{2}}}{\rm{ + }}{{\rm{H}}_{\rm{2}}}\) \({\rm{Fe}}\,{\rm{ + 2HCl}}\, \to {\rm{FeC}}{{\rm{l}}_{\rm{2}}}{\rm{ + }}{{\rm{H}}_{\rm{2}}}\)	\({\rm{Mg}}\,{\rm{ + }}\,\,{{\rm{H}}_{\rm{2}}}{\rm{S}}{{\rm{O}}_4} \to {\rm{MgS}}{{\rm{O}}_4}{\rm{ + }}{{\rm{H}}_{\rm{2}}}\) \({\rm{Zn}}\,{\rm{ + }}{{\rm{H}}_{\rm{2}}}{\rm{S}}{{\rm{O}}_4} \to {\rm{ZnS}}{{\rm{O}}_4}{\rm{ + }}{{\rm{H}}_{\rm{2}}}\)

2. By Electrolysis of Water

By this method, hydrogen is prepared on a large scale. When an electric current is passed through acidulated water, it decomposes into hydrogen and oxygen.

Hydrogen is collected at the cathode, and oxygen is collected at the anode. The ratio of hydrogen gas and oxygen collected is \(2:1\) by moles.

The setup for electrolysis of water is shown below:

3. Laboratory Preparation

In the laboratory, Hydrogen is prepared by diluting hydrochloric acid or diluting sulphuric acid with zinc granules.

Reaction:

\({\rm{Zn}}\,{\rm{ + HCl}} \to {\rm{ZnC}}{{\rm{l}}_2}{\rm{ + }}{{\rm{H}}_{\rm{2}}}({\rm{g}})\)
\({\rm{Zn + }}\,{{\rm{H}}_{\rm{2}}}{\rm{S}}{{\rm{O}}_4} \to {\rm{ZnS}}{{\rm{O}}_4}{\rm{ + }}{{\rm{H}}_{\rm{2}}}({\rm{g}})\)

Why is Granulated Zinc Preferred?

Granulated zinc contains an impurity, copper, which acts as a positive catalyst for the reaction.

Procedure

Put some zinc granules in a round bottom flask fitted with two air-tight corks with two holes. Through one hole, with the help of a thistle funnel, add dilute hydrochloric acid or dilute sulphuric acid to the zinc granules. A brisk effervescence indicates the liberation of hydrogen gas.

Laboratory Setup for Preparation of Dihydrogen

Collection of Gas

Dihydrogen gas will be collected with the help of a delivery tube through the downward displacement of water because it is lighter than water.

Commercial Preparation

By coal gasification process- This is done by passing steam over hydrocarbons or coke in the presence of a catalyst like nickel.

\({\rm{C}}{{\rm{H}}_{\rm{4}}}{\rm{ + }}{{\rm{H}}_{\rm{2}}}{\rm{O + Ni(1270}}\,{\rm{K)}} \to {\rm{CO + 3}}{{\rm{H}}_{\rm{2}}}\)

Industrially, hydrogen is prepared through Bosch’s process. It is done by passing steam over red-hot coke at a high temperature of about 1000℃. The products are carbon monoxide and hydrogen, and this mixture is called water gas.

\({\rm{C}}\,{\rm{ + }}\,{{\rm{H}}_{\rm{2}}}{\rm{O}}\,{\rm{ + Ni}}\,{\rm{(1270}}\,{\rm{K)}}\,\, \to \,\,{\rm{CO}}\,{\rm{ + }}\,{{\rm{H}}_{\rm{2}}}\)

Carbon monoxide from water gas can react with steam in the presence of ferric oxide and chromium oxide catalyst to produce more hydrogen. 

The reaction is exothermic.

The carbon dioxide produced can be separated from the water-gas mixture by dissolving the mixture at \(30\) atmospheric pressure. Carbon dioxide leaves hydrogen gas behind and dissolves in water to form carbonic acid.

By Lane’s process- When superheated steam is passed over iron filings heated to about \({\rm{1025 – 1075}}\,{\rm{K,}}\) iron is oxidised and dihydrogen gas is also evolved.

\({\rm{3Fe}}\,{\rm{ + }}\,4{{\rm{H}}_{\rm{2}}}{\rm{O}}\, \to {\rm{F}}{{\rm{e}}_3}{{\rm{O}}_4}{\rm{ + }}\,4{{\rm{H}}_{\rm{2}}} + {\rm{heat}}\)

Properties of Dihydrogen

1. It is a colourless, odourless, and tasteless gas.
2. It is the lightest gas known. It is lighter than air.
3. It is highly flammable.
4. At standard temperature and pressure, it is nontoxic.
5. It is very less soluble in water.
6. The downward displacement of water collects it.
7. It is a combustible gas but does not support combustion.

Some Compounds Containing Dihydrogen

Some compounds containing dihydrogen are explained below:

Dihydrogen Monoxide

Dihydrogen monoxide is commonly known as water. The prefix ‘dihydrogen’ shows the presence of two hydrogen atoms, and monoxide refers to a single atom of oxygen.

The chemical formula of water or dihydrogen monoxide is \({{\rm{H}}_{\rm{2}}}{\rm{O}}\).

Water is a colourless, odourless and transparent substance that is the main constituent of the water bodies and covers around \(71\% \) of the Earth’s crust. It is a vital component for all living organisms.

It is available in all three states. In solid-state, it exists as ice, in the liquid state as water and the gaseous state in the form of water vapour.

Uses of Dihydrogen Monoxide

The most important use of water is for drinking purposes and in agriculture. Other uses of water include cooking, washing, bathing, and industrial processes.

Potassium Dihydrogen Phosphate

Potassium dihydrogen phosphate is also known as monopotassium phosphate or potassium biphosphate. Its chemical or molecular formula is \({\rm{K}}{{\rm{H}}_2}{\rm{P}}{{\rm{O}}_4}\). It is a soluble salt of potassium and dihydrogen phosphate ions.

Properties of Dihydrogen Phosphate

Chemical formula	\({\rm{K}}{{\rm{H}}_2}{\rm{P}}{{\rm{O}}_4}\)
Molecular weight	\(136.086\,{\rm{g/mol}}\)
Melting Point	\({252.6^ \circ }{\rm{C}}\)
Boiling point	\({\rm{40}}{{\rm{0}}^ \circ }{\rm{C}}\)
Density	\(2.338\,{\rm{g/c}}{{\rm{m}}^2}\)

Uses of Dihydrogen Phosphate

1. It is a source of potassium and phosphorus as well as a buffering agent in fertilisers.
2. It is used in fertiliser mixtures to reduce the escape of ammonia by maintaining a low \({\rm{pH}}\)

Sodium Dihydrogen Phosphate

Sodium dihydrogen phosphate is also known as monosodium phosphate or monobasic sodium phosphate. Its chemical formula is \({\rm{Na}}{{\rm{H}}_{\rm{2}}}{\rm{P}}{{\rm{O}}_{\rm{4}}}\) It is an odourless salt that exists as white powder or crystals. It is obtained by the neutralisation of phosphoric acid.

Properties of Sodium Dihydrogen Phosphate

Chemical formula	\({\rm{Na}}{{\rm{H}}_{\rm{2}}}{\rm{P}}{{\rm{O}}_{\rm{4}}}\)
Molecular weight	\(119.98\,{\rm{g/mol}}\)
Melting point	\({212^ \circ }{\rm{C}}\)
Density	\(2.36\,{\rm{g/c}}{{\rm{m}}^{\rm{3}}}\)
Solubility	Soluble in water

Uses of Sodium Dihydrogen Phosphate

1. It is used as an emulsifier in products like processed cheese, toothpaste, evaporated milk and animal feed.
2. It plays a significant role in the application of pharmaceuticals. Upon oral consumption, it works as a urinary acidifier and helps prevent kidney stones.
3. It is used to detect magnesium ions in salts.

Ammonium Dihydrogen Phosphate

Ammonium dihydrogen phosphate is also known as monoammonium phosphate, is a chemical compound with the chemical formula \({\rm{N}}{{\rm{H}}_{\rm{4}}}{{\rm{H}}_{\rm{2}}}{\rm{P}}{{\rm{O}}_{\rm{4}}}\) It is a transparent, piezoelectric crystal containing no water of crystallisation.

Properties of Ammonium Dihydrogen Phosphate

Chemical formula	\({\rm{N}}{{\rm{H}}_{\rm{4}}}{{\rm{H}}_{\rm{2}}}{\rm{P}}{{\rm{O}}_{\rm{4}}}\)
Molecular weight	\(115.03\,{\rm{g/mol}}\)
Melting point	\({190^ \circ }{\rm{C}}\)
Boiling Point	NA
Density	\(1.80\,{\rm{g/c}}{{\rm{m}}^{\rm{3}}}\)

Uses of Ammonium Dihydrogen Phosphate

1. It is mainly used in agriculture as fertilisers.
2. It is also used in some dry chemical fire extinguishers.
3. It is used as a dough strengthener and leavening agent in baked goods.
4. It is used as a firming agent and pH control agent in condiments and puddings.

Uses of Dihydrogen

1. As a fuel- Liquid hydrogen is used as rocket fuel. It is a pollution-fuel because it gives water upon combustion.
2. Hydrogen is used for the hydrogenation of vegetable oil to prepare solid vanaspati ghee from liquid vegetable fats like groundnut oil, coconut oil, etc. This process is called the catalytic hydrogenation of oils.
3. For the manufacture of chemicals- Hydrogen is used to manufacture hydrochloric acid, methanol, urea, etc.
   It is also used in the production of ammonia gas used in the manufacture of nitric acid and fertiliser.
4. As a reducing agent- It is used to reduce the lesser reactive metals like copper, tin, lead, etc., from their respective oxides.
5. It powers the sun and many stars through the fusion of hydrogen into Helium.
6. As an oxy-hydrogen torch- Hydrogen and oxygen are burnt in a specially designed apparatus, and its flame is used for cutting and welding metals.

Summary

Through this article, we studied dihydrogen, its properties, and the preparation of dihydrogen at the laboratory and commercial levels. Also, we learned about some compounds containing dihydrogen like dihydrogen monoxide,

FAQs on Dihydrogen

Q.1. What are the uses of dihydrogen?
Ans:
1. As a fuel- Liquid hydrogen is used as rocket fuel. It is a pollution-fuel because it gives water upon combustion.
2. Hydrogen is used for the hydrogenation of vegetable oil to prepare solid vanaspati ghee from liquid vegetable fats like groundnut oil, and coconut oil. This process is called the catalytic hydrogenation of oils.
3. For the manufacture of chemicals- Hydrogen is used to manufacture hydrochloric acid, methanol, and urea.
It is also used in the production of ammonia gas used in the manufacture of nitric acid and fertiliser.
4. As a reducing agent- It is used to reduce the lesser reactive metals like copper, tin, and lead from their respective oxides.
5. It powers the sun and many stars through the fusion of hydrogen into Helium.
6. As an oxy-hydrogen torch- Hydrogen and oxygen are burnt in a specially designed apparatus, and its flame is used for cutting and welding metals.

Q.2. What are the physical properties of dihydrogen?

Ans: The physical properties of dihydrogen are –
1. It is a colourless, odourless, and tasteless gas.
2. It is the lightest gas known. It is lighter than air.
3. At standard temperature and pressure, it is nontoxic.
4. It is less soluble in nature.
5. It is collected by the downward displacement of water.
6. It is a combustible gas but does not support combustion.

Q.4. What is the common name for dihydrogen monoxide?
Ans: Dihydrogen monoxide is commonly known as water. Its chemical formula is \({{\rm{H}}_{\rm{2}}}\).

Q.5. What is disodium dihydrogen pyrophosphate?
Ans: Disodium dihydrogen pyrophosphate is also known as a dimer of sodium dihydrogen phosphate. Its chemical formula is \({\rm{Na}}{{\rm{H}}_2}{\rm{P}}{{\rm{O}}_{\rm{4}}}\) It is an odourless salt that exists as white powder or crystals. It is obtained by the partial neutralisation of phosphoric acid.

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