Hydrogen

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• Robert Boyle prepared hydrogen in 1672, by treating iron with sulphuric acid, but he could not decipher its basic nature.

• The credit of the discovery of hydrogen goes to the British chemist Henry Cavendish. He prepared the gas by the action of dil HCl with zinc in 1766. He established its elementary character and proved that when hydrogen burns in air it forms water.

• The British chemist Joseph Priestley named the gas as “inflammable air” in 1781, and the French chemist Antoine Laurent Lavoisier renamed it hydrogen, as the word means water former in Greek.

Occurrence

Hydrogen occurs in free and combined state.

• It is found trapped in certain rocks and minerals, mixed with natural gas in gold mines and in traces in volcanic gases.

• The sun and most of the stars are made of free hydrogen. It is the nuclear fusion of hydrogen atoms which produces large amount of heat and light energy.

• In combined state, 1/9^th part of water by weight consists of hydrogen. It is a vital constituent of the cells and tissues of animal and plant kingdom.

General Methods of Preparation of Hydrogen

• When metals like sodium, potassium and calcium are treated with cold water, they react violently with the formation of hydroxides and hydrogen gas.

• When metals like Mg, Al, Zn and Fe are heated to dull red heat and steam is passed over them , they form their oxides and hydrogen

• When metals like Mg, Al, Zn and Fe are treated with dil sulphuric acid,they react to form salts and hydrogen.

• When metals like Al, Zn and Sn in powdered state is boiled with conc alkali solutions ,they form soluble salts and hydrogen.

• When electric current is passed through acidulated water, hydrogen gas is liberated at the cathode and oxygen at the anode.

• When hydrides of sodium, potassium and calcium are treated with water , they react in the cold to form hydroxides and hydrogen.

Laboratory Preparation of Hydrogen

Hydrogen is prepared in the laboratory by treating granulated zinc with dilute sulphuric acid or dilute hydrochloric acid in cold.

Preparation of Hydrogen in the Laboratory