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Atomistry » Vanadium » Physical Properties » Atomic Weight | ||
Atomistry » Vanadium » Physical Properties » Atomic Weight » |
Atomic Weight of Vanadium
The early investigations into the atomic weight of vanadium provide a very interesting example of the application of Mitscherlich's Law of Isomorphism. Berzelius in 1831 obtained the value 68.5 by (a) reducing vanadic acid in hydrogen at a red heat, (b) reconverting the reduced oxide to vanadic acid. Berzelius assumed in his calculations that the formula for vanadic acid was VO3. In 1868 Roscoe pointed out that the following minerals had been shown by Rammelsberg to be isomorphous, but were not at that time represented by analogous formulae:
Roscoe carried out the first reliable determinations of the atomic weight of vanadium. He used three methods:
In 1914 Briscoe and Little again analysed vanadium oxytrichloride, using Methods (b) and (c). The ratio VOCl3:3Ag was studied in detail and gave an atomic weight of 50.950; two measurements of the ratio VOCl3:3AgCl gave an atomic weight of 50.952. The investigators state, in reviewing the possible sources of error, that the figures are likely to prove a trifle low. Hence the atomic weight of vanadium lies between 50.95 and 50.96, and the higher number is most probably the more correct. This value is in good agreement with a determination carried out in 1910 by McAdam, who employed a totally different reaction. A known weight of anhydrous sodium metavanadate was heated in a stream of hydrogen chloride gas and chlorine; the residual sodium chloride was fused and weighed. From the ratio NaVO3:NaCl an atomic weight of 50.960 was obtained. The International Committee on Atomic Weights adopted the value 51.0 in 1911. This was altered to 50.96 in 1925 and to 50.95 in 1929. The atomic number of vanadium is 23. |
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