CINF 19 |
| The mole, the kilogram, and Avogadro's constant are entangled in their current definitions and, unlike other base units, based on artifacts. A study underway by metrologists re-defines these using an exact definition of Planck's constant in conjunction with either the “Josephson constant” or “Klitzing constant” of physics, both unknown or opaque to chemists. Unit definitions play a quintessential role in the ability of beginning students through professional practitioners to understand the quantitative nature of chemistry. Through discussions within the ACS Committee on Nomenclature, Terminology and Symbols, a proposal exists to define the mole as Avogadro's number (not Avogadro's constant) of anything -- exactly 6.0221418 X 1023 (an integer, no uncertainty!) -- from which the kilogram emerges by the long-standing premise that Avogadro's number of 12C has a mass of exactly 12 grams (no uncertainty). The proposal follows the philosophy behind the 1967 definition of the second, the time required for 9,192,631,770 periods of a specified 133Cs radiation. The speed of light is similarly defined as a certain (integer) number of m/s. |
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Past, Present and Future of the Kilogram
3:30 PM-5:10 PM, Sunday, April 6, 2008 Marriott Convention Center -- Blaine Kern C, Oral
Division of Chemical Information |