c161l6_09_15 - Chapter 3 Stoichiometry: Chemical...

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Chapter 3 Chapter 3 Stoichiometry: Chemical Calculations
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Isotopes Isotopes W Different “varieties” of the same element W Which element is determined by Z, the number of protons W Which isotope is which is determined by A W All isotopes of the same element have very similar chemical properties
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Isotopic mass and Natural Abundance Isotopic mass and Natural Abundance W Atomic mass is the average of the isotopic masses W A = Σ f i a i is the natural abundance of isotope i a i is the mass of isotope i W Need another equation 1 = Σ
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Example Example W Boron has 2 isotopes: 10 B with mass 10.0129u 11 B with mass 11.0093u W What is the natural abundance of 10 B? W Solution 10.81 = f 10 (10.0129) + f 11 (11.0093) 1 = f + f 10.81 = f(10.0129) + (1-f)(11.0093) f= 0.1991 or 19.91%
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The mole W Individual atoms are in general too tiny to work with W Need a larger unit We buy eggs by the dozen Paper by the ream (about 500 sheets) Factories use the “hundred-count” Chemistry uses the mole
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This note was uploaded on 04/06/2011 for the course CHEMISTRY 161 taught by Professor Seigel during the Fall '10 term at Rutgers.

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c161l6_09_15 - Chapter 3 Stoichiometry: Chemical...

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