What are the Special forms of Hydrogen
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What are the Special forms of Hydrogen
Aug 26, 2022, 16:45 IST
Special forms of Hydrogen:
i) Nascent hydrogen: Freshly prepared hydrogen is known as nascent hydrogen and is more reactive than ordinary hydrogen.
ii) Atomic hydrogen: When hydrogen is passed through an electric arc established between two tungsten filaments, hydrogen is dissociated into atoms. This form of hydrogen is known as atomic hydrogen. Reducing power of atomic hydrogen is more than that of nascent hydrogen.
iii) Active hydrogen: It is obtained by subjecting molecular hydrogen to silent electric discharge at ordinary temperature and 0.5 mm pressure. It has great chemical activity and its half life period is similar to that of atomic hydrogen.
iv) Occluded hydrogen: It is more active than ordinary hydrogen. Hydrogen adsorbed by certain metals e.g., Pd, Pt, Fe, Co, Ni etc., is known as occluded hydrogen. One volume of finely divided metals adsorb the following volumes of hydrogen. Pd black = 870, Pt = 49.5; Au = 3, Fe = 15.7, Cu = – 4.5, Al = 2.7. Colloidal Pd takes up 2050 volumes of H 2 than itself. Occlusion decreases with rise in temperature. Order of occlusion Colloidal Pd > Pt > Au > Ni
v) Ortho and para hydrogen (Allotropes): When the spins of the two protons (nuclei) are parallel in the hydrogen molecule, it is known as ortho hydrogen (s = 1). When the spins of the two protons (nuclei) are antiparallel, it is known as para hydrogen (s = 0). Orthoform is more stable than para and para form always tends to revert in orthoform, still orthoform has not been isolated in the pure form. When ordinary H 2 is passed over activated charcoal at 20K in quartz vessel. The charcoal adsorb only para H 2 . The charcoal consists of about 99.8%, para form and may be kept for a week in glass vessel at room temperature without any appreciable change to orthoform. Thus at room temperature ordinary H 2 is an equilibrium mixture of 75% ortho and 25% para hydrogen. At low temperature, the percentage of para form increases.
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