In water, organic compounds, etc.


Lab method

  1. Action of active metals on water.
2Na + 2H2O 2NaOH + H2
2K + 2H2O 2KOH + H2
Ca + 2H2O Ca(OH)2 + H2
  1. Action of less active metals on steam –
Zn + H2O ZnO + H2
Mg + H2O MgO + H2
Over red hot iron, steam forms hydrogen
3Fe + 4 H2O Fe3O4 + 4H2

  1. From acids
Zn + H2SO4 ZnSO4 + H2
Zn + 2HCl ZnCl2 + H2

                    The intensity with which metals displace hydrogen from acids depends on a series
               K, Ca, Na,
Mg, Al, Zn, Fe,
Ni, Sn, Pb,
Cu, Hg, Ag, Au, Pt
Displace hydrogen
Displace hydrogen
Displace hydrogen

Do not displace

  1. From alkalies
Zn + 2NaOH Na2ZnO2 + H2
Zn + 2KOH K2ZnO2 + H2
2Al + 2NaOH + 2H2O 2NaAlO2 + 3H2
2Al + 2KOH + 2H2O 2KAlO2 + 3H2

The gas is dried by CaCl2

Industrial method

  1. Steam is passed over heated coke to produce water gas.
               C + H2O CO + H2
Water gas and excess steam are passed over a catalyst, iron (III) oxide.
               CO + H2 + H2O CO2 + 2H2
Carbon dioxide is absorbed by caustic soda or potash to obtain hydrogen.

  1. If water is electrolyzed, hydrogen can be collected at the cathode.



  1. It is a colorless, odorless gas.
  2. It is 0.069 times as heavy as air.
  3. It is almost insoluble in water.
  4. B.P = -253°C, M.P. = -259.4°C.
  5. Noble metals readily absorb hydrogen when finely divided.


  1. It is combustible, but does not support combustion.
2H2 + O2 2H2O
  1. Hydrogen and chlorine react explosively in direct sunlight.
H2 + Cl2 2HCl
  1. If hydrogen is passed through boiling sulfur, it forms hydrogen sulfide
H2 + S H2S
  1. Combines with nitrogen in the presence of catalysts to form ammonia.
N2 + 3H2 2NH3
  1. It reduces metal oxides
H2 + CuO H2O + Cu
H2 + PbO H2O + Pb
Fe2O3+ 3H2 3H2O + 2Fe


  1. As a fuel – in rockets, in torches. In electric arcs, it absorbs energy to split to atoms, and outside the arc it forms molecules releasing energy.
  2. In self-lighting jets – hydrogen is absorbed by finely divided metals, and heat is released, which is used to ignite fuel.
  3. In meteorological balloons.
  4. In the presence of catalysts, it is used to make petrol from coal.
  5. In the extraction of metals
WO3 + 3H2 W + 3H2O
  1. Hydrogenation of oils – If heated with oils to 150° - 200°C at 5 atmos. pressure in the presence of nickel, oils are hydrogenated to a semi-solid state.
  2. To make ammonia and hydrochloric acid by the direct combination of elements.

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