Atomic Hydrogen
Langmuir
,in 1915, obtained atomic hydrogen by dissociating on a hot filament of
tungsten or platinum. The dissociation of molecular hydrogen is an
endothermic process.
The
atomic hydrogen is stable only for a fraction of a second and
immediately reverts back to its molecular form, liberating a large
amount of energy.
Atomic
hydrogen is extremely reactive, being more reactive than ordinary,
nascent, or adsorbed oxygen. When it is passed over metals or
non-metals, it forms hydrides at normal temperatures, excepting for
nitrogen, to which it does not react.
Atomic
hydrogen is an extremely powerful reducing agent, reducing oxides
chlorides and sulphides of some metals like Ag, Hg, Cu etc. to metals at
ordinary temperature.Nascent Hydrogen
The
hydrogen gas, which is just liberated as a result of a chemical is
called nascent hydrogen or newly born hydrogen. It is obtained by
passing dihydrogen gas at atmospheric pressure through an electric arc
between two tungsten rods. The electric arc maintains a temperature
around 4000 - 4500°C. As the molecules of dihydrogen gas pass through
the electric arc, these absorb energy and get dissociated into atoms as
nascent hydrogen. It is more reactive than ordinary hydrogen and its
colour is not discharged. (pink in colour). For example, if ordinary
hydrogen is passed through acidified KMnO4
it does not get decolourised. However, if zinc pieces are added to the
same solution, bubbles of hydrogen rise up through the solution and the
colour is discharged due to the reduction of KMnO4 by nascent hydrogen.
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