11th Chemistry NCERT notes

Preparation of Dihydrogen, H2

Laboratory Preparation of Dihydrogen

  • It is usually prepared by the reaction of granulated zinc with dilute hydrochloric acid.

Laboratory Preparation of Dihydrogen

  • It can also be prepared by the reaction of zinc with aqueous alkali.

Laboratory Preparation of Dihydrogen

Commercial Production of Dihydrogen

  • By the electrolysis of acidified water

Commercial Production of Dihydrogen

  • Form water gas (Bosch process)

Commercial Production of Dihydrogen

  • From steam (Lane’s process) super-heated steam is passed over iron filings heated to about 1023-1073 k when hydrogen is formed.
  • Highly pure (> 99.95 %) dihydrogen is obtained by electrolyzing warm aqueous barium hydroxide solution between nickel electrodes.
  • From hydrocarbons by partial oxidation

Commercial Production of Dihydrogen

  • It is also obtained as a by-product in the manufacture of NaOH and chlorine by the electrolysis of brine solution.

During electrolysis, the reactions that take place are

Commercial Production of Dihydrogen

Properties of Dihydrogen

Physical Properties

  • Dihydrogen is a colourless, odourless and tasteless gas.
  • It is a combustible gas.
  • It is insoluble in water.
  • It is lighter than air.

Chemical Properties of Dihydrogen

  • Reaction with halogens: It reacts with halogens, X2 to give hydrogen halides. HX.

Chemical Properties of Dihydrogen

(F can react with hydrogen in dark also, iodine requires a catalyst)

  • Reaction with dioxygen:

Chemical Properties of Dihydrogen

The reaction is highly exothermic.

  • Reaction with dinitrogen: With dinitrogen to form ammonia

Chemical Properties of Dihydrogen

  • Reaction with metals: Here H2 acts as oxidising agent.

Chemical Properties of Dihydrogen

Where (M = alkali metal)

  • Reaction with metal ions and metal oxides: It reduces some metal ions in aqueous solution and oxides of metals (less active than iron) into corresponding metals

Chemical Properties of Dihydrogen

  • Reaction with organic compounds: It reacts with many organic compounds in the presence of catalysts to give useful hydrogenated products of commercial importance.
  • Hydrogenation of vegetable oils using nickel as catalyst gives edible fats (margarine and Vanaspati ghee).
  • Hydroformylation of olefins yields aldehydes which further undergo reduction to give alcohols.

Chemical Properties of Dihydrogen

Use of Dihydrogen

  • It is used in the manufacture of CH3OH.
  • It produces temperature of 2850oC and oxy-atomic hydrogen flame produces a temperature of 4000oC, so it is used in oxy-hydrogen flame.
  • The largest single use of H2 is in the synthesis of NH3 which is used in the manufacture of HNO3 and fertilizers.
  • Liquid hydrogen (LH2) is used as rocket fuel.
  • H2 is used as a reducing agent in extraction of metals.
  • H2 is used in fuel cell for generating electrical energy.
  • Hydrogen is used in the manufacture of synthetic petrol.

(By heating H2 with coal and heavy oils under very high pressure in the presence of catalyst).


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