AIEEE Chemistry Paper

UNIT 13 HYDROGEN
Position of hydrogen in periodic table, isotopes, preparation, properties and uses of hydrogen;

Period 1 Group 1
Atomic Number 1
Symbol H
Atomic Weight 1.0079
Discovery Cavendish, 1766
Hydrogen was prepared for many years before it was recognized as a distinct element.
Electron Configuration 1s¹
Word Origin Greek: hydro, water; genes, forming
Named by Lavoisier.

Isotopes

Protium (0 neutrons), Deuterium (1 neutron), and Tritium (2 neutrons).
Properties

Hydrogen is the most abundant element in the universe.


Hydrogen is a colorless, odorless, combustible gas.

Hydrogen gas is so light and diffusive that uncombined hydrogen can escape from the atmosphere.

Hydrogen gas ordinarily is a mixture of two molecular forms, ortho- and para-hydrogen, which differ by the spins of their electrons and nuclei.
Normal hydrogen at room temperature consists of 25% of the para form and 75% of the ortho form. The ortho form cannot be prepared in the pure state. Since the two forms of hydrogen differ in energy, their physical properties also differ.


Uses

Hydrogen is important in the proton-proton reaction and carbon-nitrogen cycle. Liquid hydrogen is used in cryogenics and in the study of superconductivity.
Great quantities are used for the fixation of nitrogen from the air in the Haber ammonia process.
Hydrogen is use in welding, for the hydrogenation of fats and oils, in methanol production, in hydrodealkylation, hydrocracking, and hydrodesulfurization.
Other applications include producing rocket fuel, filling balloons, making fuel cells, producing hydrochloric acid, and reducing metallic ores.
Deuterium is used as a moderator to slow down neutrons and as a tracer.
Tritium is used in the production of the hydrogen (fusion) bomb.
Tritium is also used in making luminous paints and as a tracer.

Sources

Hydrogen occurs in the free state in volcanic gases and some natural gases. Hydrogen is prepared by steam on heated carbon, decomposition of certain hydrocarbons with heat, action of sodium or potassium hydroxide on aluminum electrolysis of water, or displacement from acids by certain metals.