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The thick layer of air which surrounds the earth is called atmosphere.

Composition of air

S.N Gases in air Percentage by volume
1 Nitrogen 78.07
2 Oxygen 20.98
3 Carbon dioxide 0.03
4 Argon 0.85
5 Neon 0.002
6 Other inert gases 0.008
7 Water vapor 0.06


Symbol: H
Molecular formula: H2
Valency: 1
Position in periodic table: Group-1A, Period-1st
Electronic configuration: 1 (1s1)
Atomic number: 1
Atomic weight: 1.008
Molecular weight: 2.026amu
Freezing point: -259.14 °C
Boiling point: -252.87 °C


Hydrogen is a reactive element and thus does not occur much in the free state. In combined form, it is an important constituent of water, acid, alkali, and many organic compounds of vegetables and animal products.

General methods for preparation of hydrogen gas

From acids:
Metals like zinc, iron, magnesium, etc. are more electropositive than hydrogen and react with acid to produce hydrogen gas.
Zn + dil. H2SO4 → ZnSO4 +H2

From alkalis:
Hydrogen gas can be obtained from the action of metals like zinc, aluminum etc. with boiling caustic soda.
Zn + NaOH → Na2ZnO2 + H2
From water: At ordinary temperature, highly active metals like sodium, potassium, calcium, etc. react with water to liberate hydrogen gas.
2Na + 2H2O → NaOH + H2

Preparation of hydrogen gas in laboratory

When impure granulated zinc reacts with dilute sulphuric acid. They react together to form zinc sulphate and hydrogen gas. The principle reaction is as follows.
Zinc + Sulphuric acid → Zinc sulphate + Hydrogen↑
Zn + dil. H2SO4 → ZnSO4 + H2

Take a few grains of granulated zinc in Woulfe’s bottle fitted with a thistle funnel and delivery tube with corks. Put the next end of the delivery tube under water in pneumatic trough having a beehive shelf. Invert a gas jar, completely filled with water over the beehive shelf and let the end of the delivery tube into it. Pour dilute sulphuric acid through the thistle funnel. A brisk action sets in and hydrogen gas is evolved. Then hydrogen gas gets collected in the gas jar by downward displacement of water.
Zn + dil. H2SO4 → ZnSO4 + H2

If the reaction is slow then we can add a little copper sulphate solution to accelerate the reaction.


  • The apparatus should be made air tight.
  • Concentrated sulphuric acid should not be used because it produces sulphur dioxide instead of hydrogen gas.
  • Impure zinc should be used instead of pure zinc because the reaction becomes slow with pure zinc.

Test of hydrogen

To check whether the produced gas is hydrogen or not, when lighted splinter is introduced to the mouth of gas jar. The gas burs itself with a very faint pale-blue flame at the mouth of jar with pop sound and the splinter gets extinguishes.

Manufacturing of hydrogen

From methane-steam process:
When a mixture of steam and methane is passed over a heated nickel catalyst at 1200 ͦC, and compressed to 30 atmospheres, Hydrogen gas is manufactured. Methane is obtained as a byproduct of petroleum industry.
CH4 + H2O → CO + 3 H2

A catalyst is as a chemical substance which alters the rate of chemical reaction, itself remaining chemically unchanged because it does not take part in chemical reaction. The phenomenon is known as catalysis.

By the electrolysis of water:

A small amount of dilute acid is poured into a voltameter containing water to make a strong electrolyte as shown in the figure. In the electrolytic cell or voltameter iron is used as cathode while nickel is used as cathode while the nickel-plated iron acts as anode. An asbestos diaphragm separates these two electrodes from each other. This diaphragm prevents the mixing of hydrogen gas and oxygen gas. When electric current is passed, hydrogen is formed at cathode and oxygen at anode.

  • The thick layer of air which surrounds the earth is called atmosphere.
  • Hydrogen is the lightest gas, so it is found only in combined state and not in air.
  • Hydrogen gas can be obtained from the action of metals with acids, alkalis and water.
  • Hydrogen is combustible gas but not a supporter of combustion.
  • A catalyst is as a chemical substance which alters the rate of chemical reaction, itself remaining chemically unchanged because it does not take part in chemical reaction.

Questions and Answers

Click on the questions below to reveal the answers

The melting point of hydrogen is -259 degree C.

Hydrogen gas is not found in air because it is more reactive and the lightest gas known.

A British scientist, Henry Cavendish discovered hydrogen gas in 1776.

The physical properties of hydrogen are as follows: (i) It is colourless, odourlees and tasteless gas. (ii) It is lighter than air. (iii) It is slightly soluble in water. (iv) Its melting point is -259 degree C and boiling point is -253 degreeC.

The uses of hydrogen are as follows: (i) It is used as fuel in the rockets. (ii) It is used to make hydrogen torch. (iii) It is used as reducing agents in order to reduce the metal oxides into free metals.

  • Why doesn't our atmosphere leak into space?

    The density of atmosphere is too great such that it strongly pushes down on earth and resists being leaked into space
    Because Gravity of Earth is constantly attracting the atmosphere
    Our atmosphere does indeed leak into space
    The vacuum of space locks earth's atmosphere in place
  • Why does hydrogen occur in very less amount in the atmosphere in its free state?

    Because it is very reactive it bonds with other atoms
    because only 1% of total weight of earth is occupied by hydrogen
    Because it exist in duplet state
    Because it's valence electron is only 1
  • Which is not a way to produce hydrogen?

    from electrolysis of water
    From acid and base
    from active metal and water
    from acid and metal
  • What is the product other than hydrogen when reacting Zn and NaOH?

  • Which cannot produce hydrogen by reacting with water?

  • What is the test to verify hydrogen in jar?

    It makes a candle burn with pale blue flames
    It makes a candle burn less intensely
    It makes a candle burn more intensely
    It extinguishes a candle with pop sound
  • Why should we use dilute Sulphuric acid instead of concentrated Sulphuric acid during lab preparation of H2 gas with metal and acid?

    Concentrated Sulphuric acid is corrosive to skin

    It does not produce H2 gas

    Concentrated Sulphuric acid is expensive

    Concentrated Sulphuric acid is dangerous

  • Which one of the following catalyst is  needed when producing hydrogen gas from methane and steam?

    nickel catalyst
    molybdenum catalyst
    Platinum catalyst
    catalyst is not needed
  • What is water gas?

    Another name for water vapor
    Mixture of Carbon monoxide gas and water
    Mixture of water and Hydrogen gas
    Mixture of Carbon monoxide gas and Hydrogen gas
  • What happens in hydrogenation?

    Two hydrogen atoms combine to form Hydrogen gas
    Splitting of water into oxygen and hydrogen
    Vegetable ghee is turned into vegetable oil
    Unsaturated hydrocarbon combine become saturated hydrocarbons
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formula of hydrogen gas

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what is hydrogen gas

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why does hydrogen gas not occur freely in nature?

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Aashutosh Mishra

About Electrolysis of water with figure, can i get ?

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