MadSci Network: Chemistry

Re: How did Avagadro determine the number of molecules in a mole?

Date: Fri Jan 15 14:29:08 1999
Posted By: Dan Berger, Faculty Chemistry/Science, Bluffton College
Area of science: Chemistry
ID: 916345476.Ch

How did Avagadro determine the number of molecules in a mole?

Also, what are some other methods for determining Avagadro's number?

Amadeo Avogadro never determined "his number," but Avogadro's Law, postulated in 1811, was based on the 1809 work of Joseph Louis Gay-Lussac. Avogadro's Law states that, so long as temperature and pressure are equal, an equal volume of any gas will contain the same number of molecules.

Avogadro's Law was ignored until 1858, when Stanislao Cannizaro proved it experimentally by using it to determine accurate atomic weights.

Avogadro's number can be determined experimentally by observing the actual mass (usually via the momentum) of a "single" atom or molecule, then comparing that to the mass of one gram-molecular-weight (or mole of the same substance.

Methods of determining Avogadro's number are briefly listed here and here.

  Dan Berger
  Bluffton College

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