201-Chapter3-lectures

# 201-Chapter3-lectures - Chapter 3 Mass Relationships in...

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1 Chapter 3 Mass Relationships in Chemical Reactions By definition: 1 atom 12 C “weighs” 12 amu Atomic mass is the mass of an atom in atomic mass units (amu) 1 amu = 1.661 E -27 kg = 1.661 E -24 grams The average atomic mass is the weighted average of all of the naturally occurring isotopes of the element . Calculation of Average Atomic Mass Ex: Chlorine exists in two isomeric forms: 35 Cl and 37 Cl. The abundance of each isomer is 75.771 % and 24.229%, respectively. The masses of each isomer are 34.9688 amu and 36.9659 amu based on Mass Spectral analysis of 35 Cl and 37 Cl. Naturally occurring lithium is: 7.42% 6 Li (6.015 amu) 92.58% 7 Li (7.016 amu)

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2 The mole (mol) is the amount of a substance that contains as many elementary entities as there are atoms in exactly 12.00 grams of 12 C. 1 mol = N A = 6.0221415 x 10 23 = 6.022 x 10 23 Avogadro’s number ( N A ) The Mole (mol): A unit to count numbers of particles. Molar mass is the mass of 1 mole of substance in grams 1 mole 12 C atoms = 6.022 x 10 23 atoms = 12.00 g 12 C 1 12 C atom = 12.00 amu For any element: atomic mass (amu) = molar mass (grams) Ex: How many atoms are in 0.551 g of potassium (K) ? Sum of the atomic masses for the atoms in a molecule or chemical formula
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## This note was uploaded on 02/10/2011 for the course CHEM 201 taught by Professor Griffen during the Fall '09 term at Bunker Hill.

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201-Chapter3-lectures - Chapter 3 Mass Relationships in...

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