December 22, 2018 1 Comments

Hydrogen is the most abundant element in the universe. It was first discovered by Paracelsus during the reaction of sulphuric acid on iron in sixteenth century. Later on in 1766, Henry Cavendish prepared it in the Pur form and studied many of its properties. The name hydrogen, meaning the substance capable of forming water was given by Lavoisier in 1783.

Hydrogen is the lightest element and is the first memeber of the periodic table.The Chemistry of hydrogen is quite interesting as it show unique properties due to its unique electo configuration 1s.

As we all know that hydrogen never exist in single atomic form, but it used to eaxist in diatomic form. So here we are going to study its diatomic form.

1)  Dihydrogen

Hydrogen atoms cannot exist in free state thus it combine together to form a diatomic molecules, Hշ. Thus, molecular hydrogen is diatomic and is covalent in nature. In order to distinguish Hշ from H, the diatomic molecules of hydrogen is termed as dihydrogen.

1.1)  Occurrence of Hydrogen

As mentioned earlier, hydrogen is the most abundant element in the universe. In free state, hydrogen is not much abundant on earth. In air, it is found to an extent of one part in 15,00,000 parts. The gases coming out from volcanoes, coal mines and oil wells also contain free hydrogen. on earth crust it presents in water, coal, petroleum, clay and in all animals and vegetables matter. It constitute about 0.9% by weight of the earth crust. It is the ninth element in the order of abundance in earths crust.

1.2)  Isotopes of Hydrogen

The mass spectrographic studies of hydrogen reveal that it has three isotopes with the mass number 1,2 and 3. These are -

a) Protium : 

This is the ordinary hydrogen and it has atomic number 1 and mass number also 1. Naturally occurring hydrogen contain 99.985% of this isotopes.

b) Deuterium :

It is also referred as heavy water. It has atomic number 1 and the mass  2. It is present to an extent of 0.016% in the naturally occurring hydrogen.

c) Tritium :

It has atomic number 1 and mass number 3. It is  radioactiv in nature and is an extremely rare isotope.

1.3)  Preparation of Dihydrogen

i) General method

a) From water

2Na + 2HշO  ----->  2NaOH + Hշ

Mg + HշO  ------->  MgO + Hշ

b) From acids

Zn + HշSO --------> ZnSO + 

Fe + 2HCl ---------> FeClշ + 

ii) Laboratory preparation

In the laboratory dihydrogen can be prepared very conveniently by the action of dilute sulphuric acid on granulated zinc even at room temperature.

The apparatus used for this purpose is shown in image. Granulated zinc is taken in a Woulf's bottle fitted with a thistle funnel in one mouth and a delivery tube in the other. Dilute sulphuric acid is poured through the funnel. The reaction takes place at room temperature and no heating is required. The evolved Hydrogen gas is collected by the downward displacement of water.

1.4)  Properties of Dihydrogen

  • Is colourless, orderless and tasteless gas.
  • Ithas very low solubility in water.
  • It is highly inflammable and should be handled with care.
  • It is the lightest element among all the substance.
  • Its melting and boiling points are 13.957 K and 20.39 K respectively.

1.5). Usese of Hydrogen

    • The largest industrial use of Dihydrogen is in the manufacture of ammonia by Haber's process.
    • Large quantities of hydrogen are used in the hydrogenation of oils for the manufacture of vanaspati ghee. 
    • Liquid hydrogen mixed with liquid oxygen is used as a fuel for rockets in space programmes
    •  It used in the manufacture of synthetic petrol.
    • It is used in oxy-hydrogen torch for welding.
    • It is used in atomic hydrogen torch which produces temperature of the order of 4000°C and is used for welding.
    • It is used as a reducing agent in the laboratory and in various industries.

        Neet Tyari

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