Hydrogen : Nascent Hydrogen

Hydrogen being set free in a chemical reaction is often more reactive than hydrogen gas.

Expt. 8. - A little ferric chloride is added to a mixture of zinc and sulphuric acid which is evolving hydrogen; the ferric salt is rapidly reduced to a ferrous salt, as may be found by the appropriate tests:

FeCl₃ + H = FeCl₂ + HCl.

No such change is produced by bubbling gaseous hydrogen through the solution.

Zinc and dilute sulphuric acid also reduce potassium chlorate to potassium chloride, as may be found by the addition of silver nitrate.

It is usually supposed that the activity of such hydrogen, sometimes called nascent (new-born), i.e., in the act of liberation from its compounds, is due to the hydrogen being in the atomic state. Another theory is that the hydrogen is given off under a great pressure; hydrogen gas under pressure readily reduces some metallic salts (e.g., AgNO₃) in solution. It appears, however, that the nature of the chemical action producing the hydrogen is also of importance, because potassium chlorate is not reduced by sodium amalgam, which reduces nitrites to hyponitrites. Zinc reduces nitrites to ammonia in presence of alkali. Zinc amalgam is often more effective than zinc alone especially if a trace of copper salt is added, and "couples" composed of zinc with copper or iron are used for reduction purposes. Hydrogen for reducing purposes may be liberated in alkaline solution by zinc or aluminium, and in neutral (aqueous) solution by copper-zinc couple or amalgamated aluminium. Gaseous hydrogen in presence of platinum or palladium black, or especially colloidal palladium, is a good reducing agent for solutions. At higher temperatures, hydrogen gas in presence of finely divided nickel is used to produce solid fats from liquid oils, the oil taking up hydrogen. Hydrogen liberated by electrolysis at a cathode, especially of amalgamated lead, is a reducing agent.

The atomic character of nascent hydrogen is made probable by the following experiment. A stream of oxygen is allowed to bubble through a liquid around a cathode at which hydrogen is being liberated. Hydrogen peroxide is formed. Langmuir found that atomic hydrogen unites directly with oxygen to form hydrogen peroxide:

H + O₂ + H = HO-OH.

Protein crystallography
Chemistry guide
Hydrogen
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