How was the precise value of a mol determined?
The mole (abbreviated mol) is the unit chemists use to keep track of large numbers of atoms, ions, and molecules. The unit was invented to provide a simple way of reporting the huge numbers — the “massive heaps” — of atoms and molecules in visible samples. Chemists have defined a unit that gives a count of the number of atoms in a massive heap of atoms of a prticular size: 1 mole is the number of atoms in exactly 12g of Carbon 12. The mass of C12 was determined to be 1.9926e-23 g, using mass spectrometry. In order to determine the number of C12 atoms in the 12g pile, 12g is devided by the mass of a single atom, giving us the Avogadro constant of 6.022e23 atoms per mole. (source Atkins & Jones (1998) Chemistry: molecules, matter, and change. Third Ed. New York: W.H. Freeman and Co. p.
