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Hydrogen

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Overview

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. This note provide us the information about hydrogen and its preparation.
Hydrogen

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

Hydrogen

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

Occurrence

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

Principle:
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.

Precaution

  • 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.

Things to remember
  • 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.
  • It includes every relationship which established among the people.
  • There can be more than one community in a society. Community smaller than society.
  • It is a network of social relationships which cannot see or touched.
  • common interests and common objectives are not necessary for society.
Videos for Hydrogen
A special element - Hydrogen
Hydrogen: Nature
Laboratory preparation of hydrogen gas.
Laboratory Preparation Of Hydrogen
Preparation of Hydrogen from the reaction of Zinc with Hydrochloric Acid
Questions and 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.
Quiz

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