Ch 3 Stoich - C h a p te r 3 : S to i c h i o m e tr y...

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8/18/09 GT 6e Zumdahl Chapter 3 1 Chapter 3: Stoichiometry Stoichiometry : (Greek stoicheion, “element or part,” + metron , “measure”) The study of the numerical relationships of chemical formulas and reactions.
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8/18/09 GT 6e Zumdahl Chapter 3 2 Chapter 3 Stoichiometry 3.1 Atomic Masses 3.2 The Mole 3.3 Molar Mass 3.4 Percent Composition of Compounds 3.5 Determining the Formula of a Compound 3.6 Chemical Equations 3.7 Balancing Chemical Equations 3.8 Stoichiometric Calculations: Amounts of Reactants and Products 3.9 Calculations Involving a Limiting Reactant
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8/18/09 GT 6e Zumdahl Chapter 3 3 Atomic Masses 19 th Century Chemists calculated relative atomic masses 1961 modern system of atomic masses: 12 C is assigned a mass of exactly 12 atomic mass units (amu) and the masses of all other atoms are relative to this standard Mass spectrometer – accurate method to compare masses of atoms 13 12 mass C 1.0836129 mass C = M + e (70 eV) M + + 2e M + lower mass ions
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8/18/09 GT 6e Zumdahl Chapter 3 4 Non-integer Atomic Masses Protons and Neutrons have nearly the same mass, and electrons have comparatively small masses. Why the non- integer atomic masses?
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8/18/09 GT 6e Zumdahl Chapter 3 5 Isotopes of Cl: MASS abund. Halflife Particle, Energy Decay Product(s) Isotopic Mass 0 47 200 nsec B-/B- n,14.700 Ar-47 / Ar-46 46.987976 046 0.22 sec B-/B-n,6.900 Ar-46 / Ar-45 45.984111 045 400 msec B-/B-n,10.800 Ar-45 / Ar-44 44.979710 044 0.43 sec B-/B- n,3.920 Ar-44 / Ar-43 43.978539 043 3.3 sec B-,7.950 MeV Ar-43 42.974202 042 6.8 sec B-,9.430 MeV Ar-42 41.973172 041 38.4 sec B-,5.730 MeV Ar-41 40.970649 040 1.35 min B-,7.480 MeV Ar-40 39.970413 039 55.6 min B-,3.442 MeV Ar-39 38.968008 038 37.24 min B-,4.917 MeV Ar-38 37.968010 037 24.23% Stable 36.9659 036 3.01E+5 yr B- /EC,10.413 Ar-36 / S-36 35.9683 035 75.77% Stable 34.9688 034 1.5264 sec EC,5.492 MeV S-34 33.97376 033 2.511 sec EC,5.583 MeV S-33 32.97745 032 298 msec EC/ECa/ECp,12.6 85 S-32 / Si-28 / P-31 31.985688 031 150 msec EC/ECp,11.9 80 S-31 / P-30 30.9924 17 35.45 Cl Chlorine
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8/18/09 GT 6e Zumdahl Chapter 3 6 Mass Spectrometry and Isotopes Mass Spectrometer accelerates ions (or molecular ions) in an electric field and then separates those ions by relative mass in a magnetic field Mass Spectrometer Separation of Chlorine 0 20 40 60 80 100 35 37 Relative Mass Relative Amount 17 35.45 Cl Chlorine
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8/18/09 GT 6e Zumdahl Chapter 3 7 • The mole is defined as the number of carbon atoms (isotope 12 C) in exactly 12 grams of pure 12 C. • How many atoms is this? • We can have a mole of anything, it just represents a quantity. • What is the mass of 1 carbon atom? Atoms and the Mole
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8/18/09 GT 6e Zumdahl Chapter 3 8 Mole is an abbreviation of “gram mole cular weight” The mass, in grams, of a mole of atoms of an element is numerically equal to the relative atomic mass of that element (relative to carbon) We frequently will express atomic and molecular masses with the units g/mol Moles and Mass
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8/18/09 GT 6e Zumdahl Chapter 3 9 Molar Mass Relative Molecular Mass of a molecule equals the sum of the relative atomic masses of all of the atoms making up the molecule.
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Ch 3 Stoich - C h a p te r 3 : S to i c h i o m e tr y...

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