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8. Show by argument that the reciprocal of Avogadro's constant is the gram equivalent of 1 atomic mass unit. Solution:
By definition one gram atomic weight of 12C is 12 gfmol. Thus the mass of one atom of 12Cis M r~C) = Na12g/mol = "12 g/atom. atoms/mol N:
But by definition, one atom of 12Chag a magsof 12 u. Therefore, 9. How many atoms of 234Uare there in 1 kg of natural uranium? Solution:
From Table A.3, the natural abundance of 234Uin uranium is found to be f(234U) = 0.0055 atom-%. A mass m of uranium contains [m/ A(U)]Na uranium atoms. Thus, the number of 234Uatoms in the mass m = 1000g are = 1.392 X 1020 atoms. 10. How many atoms of deuterium are there in 2 kg of water? Solution:
Water is mostly H2O, and so we first calculate the number of atoms of hydrogen N(H) in a mass m = 2000g of H2O is N(H) = 2N(H2O) = 2 = 1.34 X 1026atoms of H. From Table A.4, the natural isotopic abundance of deuterium (D) is 0.015 atom-% in elemental hydrogen. Thus, the number of deuterium atoms in 2 kg of water is N(D) = 0.00015 x N(H) = 2.01 X 1022 atoms. July 24, 2002 ...
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