Hydrogen

Hydrogen

Symbol	H
Atomic Number	1
Atomic Mass	1.008
Discovered by	Hydrogen was discovered by Henry Cavendish

Physical Properties of Hydrogen

What is Hydrogen?

• To start the tour with the periodic table of elements, the first element to come across is Hydrogen, whose chemical symbol is H. It is the first and most basic among all the elements in the universe. It is also the lightest element in the periodic table, and 90% of all the atoms in the universe are hydrogen atoms.
• The chemist Lavoisier gives the name hydrogen. It got its name from the Greek word “hydro” meaning water. Lavoisier knew that it existed in every water molecule.

Preparation of Dihydrogen – H₂

1. Laboratory Preparation of Dihydrogen

(i) Typically, hydrogen is created when powdered zinc reacts with diluted hydrochloric acid.

Zn + 2H⁺ → Zn²⁺ + H₂

(ii) Zinc and aqueous alkali can also be combined to create hydrogen. The reaction is given below:

Zn + 2NaOH → Na₂ZnO₂ + H₂

2. Commercial Production of Dihydrogen

Below is a list of methods that are frequently used:

i) Using platinum electrodes, acidified water is electrolysed to produce hydrogen.

Detailed Physical Properties of Hydrogen

• It is a gas with no colour and odour and has the lowest density of all gases. It is seen as the clean fuel of the future, which is generated from water and returned to water when oxidized.
• It is present in water and in almost all molecules in living things. It remains bonded with carbon and oxygen atoms. It can be said that it is the most abundant element in the universe.
• It is present as a gas in the atmosphere in one part per million volumes. Hydrogen is spotless and is non-toxic and safe to produce from various different sources, transport, and store in large amounts.
• It is named an energy carrier because it stores energy which is first created somewhere else.
• This element was artificially produced in the 16th century. It was named as hydrogen whose Greek name is ‘water-former’

(ii) By electrolysing brine solution, it is produced as a byproduct in the production of sodium hydroxide and chlorine. The reactions that take place during electrolysis are:

At anode: 2Cl^–(aq) → Cl₂(g) + 2e^–
At cathode: 2H₂O(l) + 2e^– → H₂(g) + 2OH^–(aq)

The overall reaction is

2Na⁺ (aq) + 2Cl^– (aq) + 2H₂O(l) → Cl₂ (g) + H₂ (g) + 2Na⁺ (aq) + 2OH^– (aq)

Chemical Properties of Hydrogen

The following reactions can be used to demonstrate the chemistry of dihydrogen:

1. Reaction with X₂ (Halogens): It produces hydrogen halides (HX) after reacting with halogens (X₂).

X₂(g) + H₂(g) + → 2HX(g)

Where X = Cl, F, I, Br

2. Reaction with O₂ (dioxygen): Water is created when it reacts with dioxygen. The reaction produces a lot of heat.

3. Reaction with N₂(dinitrogen): It forms ammonia with dinitrogen.

4. Reactions with metal oxides and metal ions: It reduces some metal oxides and metal ions in aqueous solutions into the appropriate metals.

For example, Pd₂⁺(aq) + H₂(g) → 2H⁺(aq) + Pd(s)

5. Reactions with metals (M): It reacts at a high temperature with various metals to produce the corresponding hydrides.

H₂(g) + 2M(g) → 2MH(s)

Where M is an alkali metal.

Uses of Hydrogen

• Ammonia synthesis is the most significant use of hydrogen.
• A large amount of hydrogen is consumed in the catalytic hydrogenation of vegetable oils to extract solid fat.
• It is also consumed as rocket fuel when combined with oxygen, and as a rocket propellant by nuclear energy.
• Hydrogen is burnt as a fuel to burn in internal combustion engines.