Zumdahl+Chapter+3+Lecture+Notes

Zumdahl+Chapter+3+Lecture+Notes - Chapter 3 Stoichiometry...

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8/26/07 Zumdahl Chapter 3 1 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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8/26/07 Zumdahl Chapter 3 2 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 = Mass of 13 C = 13.003 amu M + e (70 eV) M + + 2e M + lower mass ions
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8/26/07 Zumdahl Chapter 3 3 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 3 1
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8/26/07 4 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 35 Cl contains 17 protons and 18 neutrons 37 Cl contains 17 protons and 20 neutrons 1 1 + 2 2 + ... + n n Average Relative Atomic Mass = A P A P A P Chlorine = 35.45
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8/26/07 Zumdahl Chapter 3 5 Atoms Avogadro’s Number is the number of 12 C atoms in exactly 12 grams of carbon N 0 = 6.0221420 X 10 23 The mass, in grams, of Avogadro's number of atoms of an element is numerically equal to the relative atomic mass of that element (relative to carbon) = mass of atom C
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8/26/07 6 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 relative molecular mass of CO = 2 mass CO molecule 2
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8/26/07 Zumdahl Chapter 3 7 Moles A mole measures the chemical amount of a substance Mole is an abbreviation of “gram mole cular weight” One mole of a substance equals the amount that contains Avogadro's number of atoms or molecules. One mole = Molar mass (M) of that element or molecule, expressed in grams For example, the Molar Mass (M) of carbon dioxide ( CO 2 ) is M = (1*12) + (2 * 16) = 44 = 44g/mole = 1 mole
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8/26/07 Zumdahl Chapter 3 8 Molecules of isoamyl acetate have the formula C 7 H 14 O 2 . Calculate (a) how many moles and (b) how many molecules are present in 0.250 grams of isoamyl acetate.
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