Labratory preparation of hydrogen
In the laboratory, [ H2 is usually prepared by the reaction of acids on metals such as zinc with Kipp's apparatus.
Zn + 2 H+ ? Zn2+ + H2
Aluminium can also produce H2 upon treatment with bases:
2 Al + 6 H2O + 2 OH- ? 2 Al(OH)-
4 + 3 H2
The electrolysis of water is a simple method of producing hydrogen. A low voltage current is run through the water, and gaseous oxygen forms at the anode while gaseous hydrogen forms at the cathode. Typically the cathode is made from platinum or another inert metal when producing hydrogen for storage. If, however, the gas is to be burnt on site, oxygen is
desirable to assist the combustion, and so both electrodes would be made from inert metals. (Iron, for instance, would oxidize, and thus decrease the amount of oxygen given off.) The theoretical maximum efficiency (electricity used vs. energetic value of hydrogen produced) is in the range 80–94%.[75]
2 H2O(l) ? 2 H2(g) + O2(g)
In 2007, it was discovered that an alloy of aluminium and gallium in pellet form added to water could be used to generate hydrogen. The process also creates alumina, but the expensive gallium, which prevents the formation of an oxide skin on the pellets, can be re-used. This has important potential implications for a hydrogen economy, as hydrogen can be produced on-site and does not need to be transported ]
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Asked 4/18/2012 12:57:27 PM
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