Ch2(9)-3(6)Sep8Fa08a

Ch2(9)-3(6)Sep8Fa08a - CHEM 109 General Chemistry...

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CHEM 109 General Chemistry University of Nebraska FALL 2008 8 September 2008 Announcements: UTAC Sessions: Avery 119: 6pm Tues or 4pm Thurs OR Burnett 103 5pm Wed
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Counting Atoms: The Counting Atoms: The Mole Mole _____: the amount of substance that contains as many elementary entities (atoms, molecules, or other particles) as there are atoms in exactly 12 g of 12 C ____________________ But how many atoms are there in 12 g of 12 C? Well, using a mass spectrometer, it was determined that 1 atom of 12 C = 1.992646 x 10 -23 g So, let’s do the math…
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The Mole (aka Avogadro’s Number) The Mole (aka Avogadro’s Number) Avogadro’s number is a conversion unit: “items” = molecules, atoms, students, bugs, etc… The symbol is N A = 6.022 x 10 23 “items”/mol
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Molar Mass Molar Mass We must take into account all the isotopes of each element and their percent abundance . Molar mass of an element is a weighed average of the masses of all the isotopes of one element. Once calculated, it is the mass of ___________________________ of that element.
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Example The mass spectral analysis of an iron sample gives the following data. Calculate the molar mass of iron (Fe). 54 Fe 53.940 g/mol 56 Fe 55.935 g/mol 57 Fe 56.935 g/mol 58 Fe 57.933 g/mol
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Molar Mass Molar Mass The molar mass (g/mol) of an element is always numerically equal to its weighted average atomic mass (in amu). A mole can be thought of as a unit of measure, similar to a dozen 1 dozen eggs means 12 eggs; 1 dozen cookies means 12 cookies Both have the same number but different masses Atomic mass versus Molar mass
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Mole and Mass Relationships Substance Weight of 1 atom Pieces in 1 mole Weight of 1 mole hydrogen 1.008 amu 6.022 x 10 23 atoms 1.008 g carbon 12.01 amu 6.022 x 10 23 atoms 12.01 g oxygen 16.00 amu 6.022 x 10 23 atoms 16.00 g sulfur 32.06 amu
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Ch2(9)-3(6)Sep8Fa08a - CHEM 109 General Chemistry...

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