Hydrogen

Position of Hydrogen in the Periodic Table 

It is the first element in the periodic table. It shows similarity with alkali metals and halogens as well. Although in recent researches and experiments, scientists have found hydrogen in its metallic form. It has one electron in its outermost shell, like other alkali metals and forms monovalent ion H+. but in terms of ionization energy, it resembles halogens. 


Occurrence of Hydrogen 

Hydrogen is the most abundant element in the universe. It is found in its molecular form as dihydrogen. It comprises 70% of the total mass of the universe. It is the principal element of the solar system. The large planets such as Jupiter and Saturn are mainly composed of hydrogen. In the combined form it constitutes 15.4% of the earth’s crust and the oceans. 


Discovery of Hydrogen 

Hydrogen was discovered by English Scientist Henry Cavendish in 1766. He gave it the name ‘inflammable air’. French chemist Antoine Lavoisier named it hydrogen in 1783. 


Isotopes of Hydrogen 

Isotopes 

Atomic Number 

Atomic Mass 

Number of Neutrons

Number of Protons 

Symbol 

Protium 

1

1

0

1

11H

Deuterium 

1

2

1

1

12H

Tritium 

1

3

2

1

13H


All three isotopes of hydrogen have the same electronic configuration. That’s why they show almost the same chemical properties. but they differ largely in their physical properties due to difference in their mass numbers. Out of all three isotopes protium is the most common isotope of hydrogen which is abundantly found in nature. 


Preparation of Hydrogen 

Dihydrogen can be prepared by following methods –

  • Laboratory methods to prepare dihydrogen 

  • Commercial methods to prepare dihydrogen 

Laboratory methods to prepare dihydrogen – Following two methods are used in preparation of dihydrogen –

  • Reaction of granulated zinc with dilute hydrochloric acid – Dihydrogen can be prepared by reaction of granulated zinc and dilute HCl in laboratories. Reaction is given below –

Zn + 2H+ 🡪 Zn2+ + H2

  • Reaction of zinc with aqueous alkali – Dihydrogen can also be prepared by reaction of zinc and aqueous alkali in laboratories. After the reaction, we get sodium zincate as a product. Reaction is given below –

Zn + 2NaOH 🡪 Na2ZnO2 + H2

Commercial methods to prepare dihydrogen – Commonly used methods for commercial production of dihydrogen are listed below –

  • Electrolysis of acidified water using platinum electrodes gives hydrogen. Reaction is given below –

2H2O 🡪 2H2 + O2

  • It can be prepared by the electrolysis of aqueous barium hydroxide solution using nickel electrodes. Thus, obtained dihydrogen is highly pure in nature. 

  • When sodium hydroxide and chlorine are manufactured then dihydrogen is produced as byproduct in the reaction. 

  • It can also be produced by the reaction of steam on hydrocarbons or coke at high temperatures in the presence of catalyst. Reactions are given below –

CnH2n+2 + nH2O  1270K,Ni→ nCO + (2n+1)H2

  • Bosch process - In this method, water gas (CO + H2) is mixed with twice its volume of steam and passed over heated catalyst Fe2O3 in the presence of a promoter Cr2O3 or ThO2 at 773 K when CO2 and H2 are obtained. CO2 is removed by dissolving it in water under pressure (20-25 atm) and H2 left undissolved is collected. About 18% of the world’s production of H2 is obtained from coal.

C + H2O 🡪 CO + H2

H2 + CO + H2O 🡪 CO2 + 2H2

  • Lane’s process - By passing steam over spongy iron at 773-1050 K. reaction is given below –

3Fe + 4H2O 🡪 Fe3O4 + 4H2

Fe3O4 so produced is reduced back iron with water and this reaction is known as vivification reaction. Equation is given below –

Fe3O4 + 4H2 🡪 3Fe + 4H2

Fe3O4 + 4CO 🡪 3Fe + 4CO2


Properties of Dihydrogen 

Physical Properties of Dihydrogen are Listed Below –

  • It is a colourless, tasteless and odourless gas. It is insoluble in water. It is highly combustible. It is lighter than air. 

  • Its melting point is 13.96K. 

  • Its boiling point is 20.39K. 

  • Its density is 0.09 g/L. 

  • Its enthalpy of fusion is 0.117 kJ/mol.


Chemical Properties of Dihydrogen are Listed Below

Dihydrogen is quite stable and dissociates into hydrogen atoms only when heated above 2000 K, H2 🡪 H + H. Its bond dissociation energy is very high. For dihydrogen ∆H = 435.9kJ/mol. Due to its high bond dissociation energy, it is not very reactive. However, it combines with many elements or compounds. It shows following reactions –

  • Reaction with Metals – It reacts with metals and forms corresponding hydrides. For example, it reacts with sodium and forms sodium hydride. Reaction is given below –

2Na + H2 🡪 2NaH

  • Reaction with Non-Metals – It reacts with non – metals and forms respective products. Few of its reactions with various non – metals are given below –

2H2 + O2 🡪 2H2O

N2 + 3H2 🡪 2NH3

H2 + Cl2 🡪 2HCl 

  • Reaction with unsaturated hydrocarbons – It reacts with unsaturated hydrocarbons such as ethylene and acetylene to give saturated hydrocarbons. Reaction is given below –

H2C=CH2 + H2 Ni, 473K→ CH3-CH3

HCCH + 2H2 Ni, 473K→ CH3-CH3

This reaction is used in the hydrogenation or hardening of oils. The vegetable oils such as groundnut oil or cotton-seed oil are unsaturated in nature because they contain at least one double bond in their molecules. Dihydrogen is passed through the oils at about 473 K in the presence of catalyst to form solid fats. The vegetable ghee such as Dalda, Rath, etc. are usually prepared by this process.

Vegetable oil + H2 Ni, 473K→  Fat 


Uses of Dihydrogen 

  • It is used as a reducing agent. 

  • It is used in the hydrogenation of vegetable oils. 

  • It is used as a rocket fuel in the form of liquid hydrogen. 

  • It is used in the manufacturing of synthetic petrol. 

  • It is used in the Haber’s process of preparation of ammonia. 

  • It is used in the preparation of HCl. Reaction is given below –

H2 + Cl2 🡪 2HCl

  • It is used in the synthesis of methyl alcohol. Reaction is given below –

H2 + CO + H2 ZnO.CrO3 CH3OH

  • It is used in production of metal hydrides. 

  • It is used in the manufacture of vanaspati fats. 

  • It is used in metallurgical processes of heavy metals. 

  • Atomic hydrogen and oxy – hydrogen torches find use for cutting and welding purposes. 

  • It is used as rocket fuel in space research. 

  • It is used in fuel cells for generating electrical energy. 


Hydrogen Peroxide 

It is an important compound of hydrogen and oxygen which is mainly used in pollution control treatment of domestic and industrial effluents. It was discovered by French Chemist Thenard. 

Preparation of hydrogen peroxide – It can be prepared by following methods –

  • Acidifying barium peroxide and removing excess water by evaporation under reduced pressure gives hydrogen peroxide. Reaction is given below –

BaO2.8H2O + H2SO4 🡪 BaSO4 + H2O2 + 8H2O

  • Peroxodisulphate obtained by electrolytic oxidation of acidified sulphate solutions at high current density, on hydrolysis yields hydrogen peroxide. Reaction is given below –

2HSO4- Electrolysis→ HO3SOOSO3H Hydrolysis→ 2HSO4- + 2H+ + H2O2

  • Industrially, it is prepared by the auto – oxidation of 2-alkyllanthraquinols. 

2-ethylanthraquinol O2 H2O2 + oxidized product 


Properties of Hydrogen Peroxide – Its Physical And Chemical Properties Are Listed Below –

Physical Properties -

  • It is a colorless compound. 

  • It is miscible in water. 

  • Pure hydrogen peroxide is a pale blue syrupy liquid. 

  • It freezes at – 0.5°C and has a density of 1.4 in pure state. 

  • Hydrogen peroxide is diamagnetic. 

  • It is more highly associated via hydrogen bonding than water. 

  • Although it is a better polar solvent than H2O. However, it can’t be used as such because of strong autooxidation ability.

  • Dipole moment of H2O2 is 2.1 D. 


Chemical Properties –

  • It acts as an oxidizing as well as reducing agent in both acidic and alkaline media. 

2FeSO4 + H2SO4 + H2O2 🡪 Fe2(SO4)3 + 2H2O (in acidic medium as oxidizing agent)

  • Pure hydrogen peroxide is an unstable liquid and decomposes into water and oxygen either at room temperature or on heating. Reaction is given below –

2H2O2 🡪 2H2O + O2   ∆H= -196 kJ


Uses of Hydrogen Peroxide 

Few uses of hydrogen peroxide are listed below –

  • It acts as a bleaching agent due to release of nascent oxygen. It used to bleach delicate materials like silk, wool, leather etc. It is used as a hair bleach as well. 

  • It is used in manufacturing of many chemicals such as sodium perborate and per carbonate etc. 

  • It is used in synthesis of hydroquinone, tartaric acid etc. 

  • It is used in environmental chemistry. for example, in pollution control treatment of domestic and industrial effluent. 


Structure of Water 

Water is the oxide of hydrogen. It is an important component of animal and vegetable matter. Water constitutes about 65% of our body. It is the principal constituent of earth’s surface. Its structure is given below –

(Image to be added soon)

Due to the presence of lone pairs, the geometry of water is distorted, and the H-O-H bond angle is 104.5°, which is less than the normal tetrahedral angle (109.5°). The geometry of the molecule is regarded as angular or bent. In water, each O-H bond is polar because of the high electronegativity of oxygen (3.5) in comparison to that of hydrogen (2.1). The resultant dipole moment of the water molecule is 1.84D. In ice, each oxygen atom is tetrahedrally surrounded by four hydrogen atoms (two by covalent bonds and two by hydrogen bonds). The resulting structure of ice is the open structure having a number of vacant spaces. Therefore, the density of ice is less than that of water and ice floats over water. 


Hard and Soft Water

Soft water - Water which produces lather with soap solution readily is called soft water. e.g. distilled water, rain water and demineralised water. 

Hard water - Water which does not produce lather with soap solution readily is called hard water. e.g. sea water, river water, well water and tap water


Type of Hardness of Water 

The hardness of water is of two types –

  1. Temporary hardness 

  2. Permanent hardness 

Temporary Hardness - This is due to the presence of bicarbonates of calcium and magnesium. It is also called carbonate hardness. 

Permanent Hardness - This is due to the presence of chlorides and sulphates of calcium and magnesium. It is also called non-carbonate hardness.  


Heavy Water 

Chemically heavy water is deuterium oxide D2O. It was discovered by American scientist and Nobel Laureate Harold Urey. It is obtained as a by-product in some industries where H2 is produced by the electrolysis of water. Heavy water (D2O) is used –

  1. as a moderator and coolant in nuclear reactors 

  2. in the study of mechanism of chemical reactions 

  3. as a starting material for the preparation of a number of deuterium compounds. For example – SO3 + D2O 🡪 D2SO4

preparation of heavy water – It is prepared by the exhaustive electrolysis of water. 

Comparison Between Properties Of Water And Heavy Water 

Property 

Ordinary water (H2O)

Heavy water (D2O)

Molecular mass 

18.015

20.028

Maximum density (g cm-3

1

1.106

Melting point (K)

273.2

276.8

Boiling point (K)

373.2

374.4

Heat of fusion at 273K

6.01 kJ/mol

6.28 kJ/mol

Heat of vaporization at 373K

40.66 kJ/mol

41.61 kJ/mol

Heat of formation 

-285.9 kJ/mol

- 294.6 kJ/mol

Ionization constant 

1.008 10-14

1.95 10-15


This ends our coverage on the topic “Hydrogen”. We hope you enjoyed learning and were able to grasp the concepts. You can get separate articles as well on various subtopics of this unit such as permanent hardness and temporary hardness, hydrogen peroxide etc. on Vedantu website. We hope after reading this article you will be able to solve problems based on the topic. If you are looking for solutions of NCERT Textbook problems based on this topic, then log on to Vedantu website or download Vedantu Learning App. By doing so, you will be able to access free PDFs of NCERT Solutions as well as Revision notes, Mock Tests and much more.