ICSE Revision Notes for Study of the First Element: Hydrogen Class 9 Chemistry

Chapter Name

Study of the First Element: Hydrogen

Topics Covered

  • Dual Nature of Hydrogen 
  • Preparation of Hydrogen – General Methods 
  • Preparation of Hydrogen - Laboratory method
  • Manufacture of Hydrogen – By the Electrolysis of Water 
  • Bosch Process
  • Reaction of Hydrogen with Hydrogen (Haber process) 
  • Uses of Hydrogen

Related Study


Hydrogen is the first element of the periodic table. It was discovered by Cavendish and named by Lavoisier. 

  • Hydrogen belongs to the first group and the first period of the periodic table.
  • Although the properties of hydrogen should be similar to those of the other members of the first group, this is not the case.
  • Some of the properties of hydrogen resemble the properties of Group IA elements (Alkali metals), and some of the properties resemble the properties of Halogens (VIIA). 
  • Thus, hydrogen was put at the top of the periodic table so that the symmetry of the modern periodic table is not disturbed. 

Dual Nature of Hydrogen 

Hydrogen has an electronic configuration of 1. 

  • Hydrogen loses 1 electron and behaves like electropositive alkali metals [Group 1 (IA)]. 
  • Hydrogen gains 1 electron and behaves like electronegative halogens [Group 17 (VIIA)].

Similarity of Hydrogen with Alkali Metals and Halogens

- Similarity of hydrogen with alkali metals [Group 1 (A)] Similarity of hydrogen with halogens [Group 17 (VIIA)]
Electronic configuration Electronic configuration = 1. Thus, there is 1 electron in the outermost valence shell.

H = 1; Li = 2, 1; Na = 2, 8, 1; K = 2, 8, 8, 1

One electron less than the nearest noble gas.

H = 1 (He = 2)

F = 2, 7 (Ne = 2, 8)

Cl = 2, 8, 7 ( Ar = 2, 8, 8)

Ion formation Electropositive character exhibited.

H – 1e- → H1+

Li – 1e- → Li1+

Na – 1e- → Na 1+

Electronegative character exhibited.


H + 1e- → H1-

F + 1e- → F1-

Cl + 1e- → Cl1-

Valency Electrovalency of one exhibited.

H1+, Li1+, Na1+

Electrovalency and covalency exhibited.

Hydrogen forms

NaH (electrovalent)

CH4 (covalent)

Chlorine forms

NaCl (elecrovalent)

CCl4 (covalent)


Strong affinity for non-metals.

Examples: O, S, Cl

Hydrogen forms H2O, H2S, HCl

Sodium forms Na2O, Na2S, NaCl

Reducing agent Acts as a reducing agent.


CuO + H2 → Cu + H2O


CuO + 2Na → Cu + Na2O

Atomicity -

Diatomic molecules are formed (Two atoms linked by a single bond).


H : H or H – H → H2


Cl: C: or Cl – Cl → Cl2

Preparation of Hydrogen – General Methods 

1. General methods – From cold water and metals 

Metals react with cold water to form metal hydroxide and liberate hydrogen gas. 


2K + 2H2O → 2KOH + H2↑ 

2Na + 2H2O → 2NaOH + H2↑ 

Ca + 2H2O → Ca(OH)2 + H2↑ 

2. General methods – From boiling water/steam and metals 


Mg + H2O → MgO + H2 ↑

(boiling water)

Mg, Al, Zn and Fe do not react with cold water. They react with boiling water and liberate hydrogen gas, but the reaction is very slow.

Mg, Al, Zn and Fe react with hot steam in the heated state and form the corresponding oxide and hydrogen gas.

Iron reacts with steam, and the reaction is reversible.


2Al + H2O → Al2O3 + 3H2 ↑



Zn + H2O   →   ZnO + H2 ↑



Fe + 4H2O ⇌  Fe3O4 + 4H2


3. General methods - Forms acids


Mg + HCl → MgCl+ H2 ↑


2Al + 3H2SO4 → Al2(SO4)3 + 3H2


Zn + H2SO4 → ZnSO4 + H2


Fe + 2HCl → FeCl+ H2 ↑

4. General methods - From concentrated alkalis


2Al + 6NaOH → 2Na3AlO+ 3H2 ↑

(Sodium aluminate)

2Al + 2KOH + 2H2O → 2KAlO2 + 3H2 ↑

(Potassium meta aluminate)


Zn + 2NaOH → Na2ZnO2 + H2

(Sodium zincate)

Zn + 2KOH → K2ZnO2 + H2

(Potassium zincate)


Pb + 2NaOH → Na2PbO2 + H2

                           (Sodium plumbate)

Preparation of Hydrogen - Laboratory method

Laboratory method by using granulated zinc, dilute hydrochloric acid or dilute sulphuric acid. 


Zn + 2HCl → ZnCl2 + H2

Zn + H2SO4 → ZnSO4 + H2↑ 


Hydrogen gas is collected by the downward displacement of water.

Manufacture of Hydrogen – By the Electrolysis of Water 

  • Hydrogen is commercially obtained by the electrolysis of water. 
  • Water is a poor conductor of electricity. Thus, a less volatile acid such as sulphuric acid is added to water to make it a good conductor of electricity. This is called acidulated water
  • On passing electric current through this acidulated water, water dissociates.
    H2⇌ H++ OH 

H+, being positively charged, moves towards the cathode (negatively charged electrode). 

At cathode, 

H++ e→ H 

H + H → H2 

At anode, 

OH− e− → OH 

OH + OH → H2O + O 

O + O → O2 

Hence, water dissociates to give hydrogen and oxygen by passing an electric current through acidulated water.

 2H2O → 2H2 + O2

Bosch Process

The Bosch process consists of the following steps. 

Step 1:

Steam is passed over hot coke (at 1000°C) in a special type of furnace called a converter to form carbon monoxide and hydrogen gas. This mixture is called water gas. 

Step 2:

Excess of steam is mixed with water gas, and the entire mixture is passed over heated ferric oxide and chromic oxide. Ferric oxide acts as a catalyst and chromic oxide as a promoter.

Step 3:

In this step, carbon dioxide is removed from the reaction mixture. The mixture of carbon dioxide and hydrogen is forced through cold water under pressure at 30 atmospheric pressure or through caustic potash solution, which dissolves carbon dioxide leaving behind hydrogen gas. 

2KOH + CO→ K2CO+ H2O

Step 4:

In this last step, the mixture is passed through ammoniacal solution of cuprous chloride solution so as to dissolve carbon monoxide. Thus, hydrogen gas is obtained. 

CuCl + CO + 2H2O → CuCl.CO.2H2O

Physical Properties of Hydrogen 

  • Colourless, odourless and tasteless gas. 
  • Non-poisonous. 
  • Solubility is very low. 
  • It can be liquefied. 
  • Vapour density is 1, much lighter than air. 

Chemical Properties of Hydrogen 

  • It is neutral to litmus. 
  • It is combustible but does not support combustion. 
  • Nascent hydrogen: Fresh hydrogen formed at the time of generation is called nascent hydrogen. 

Reaction of Hydrogen with oxygen 

Hydrogen burns with a pop sound in oxygen and burns with a pale blue flame forming water. 

2H+ O→ 2H2

Reaction of Hydrogen with Chlorine 

Reaction of Hydrogen with Hydrogen (Haber process) 

Three volumes of hydrogen and one volume of nitrogen react at temperature 450 - 500° C at a pressure of 200 – 900 atm in the presence of finely divided iron (catalyst) and molybdenum (promoter).
Reaction of Hydrogen with Sulphur 

Hydrogen gas when passed through molten sulphur reacts to give another gas, hydrogen sulphide. 

H2 + S → H2S

Reaction of Hydrogen with metals 

Dry hydrogen when passed over heated metals, such as Na, K and Ca, reacts to give their corresponding hydrides. 

 2K + H→ 2KH 

 2Na + H→ 2NaH 

 Ca + H2 → CaH2 

Reaction of Hydrogen with metallic oxides 

Hydrogen reduces metal oxides to give metals; thus, hydrogen is a reducing agent. 

Fe2O3 + 3H2 → 2Fe + 3H2O

Fe3O4 + 4H→ 3Fe + 4H2O

PbO + H2 → Pb + H2O

CuO + H2 → Cu + H2O

Uses of Hydrogen 

  • As a fuel in oxy-hydrogen blow torch 
  • In meteorological balloons 
  • In the manufacture of ammonia 
  • In the manufacture of hydrogenated oils 
  • For producing artificial petrol from coal 
  • In the extraction of metals 
  • As a reducing agent

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