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THE MOLE
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MEASURING MATTER 3 ways to measure things: count: 1 dozen = 12 apples
mass: 1 dozen = 2 kg of apples volume: 1 dozen = 0.20 bushel (for typical wicker basket) We need to measure ATOMS!
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IMPOSSIBLE, IMPRACTICLE!
MASS OF 1 CARBON ATOM 1 amu = one proton or one neutron = 1.66 x g carbon has 12 protons & neutrons mass of one C atom = x g IMPOSSIBLE, IMPRACTICLE!
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MASS OF 1 CARBON ATOM One atom cannot be weighed.
Can we weigh many atoms and still compare one atom to another? …
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Mass ratio ( 2 : 7 ) is always
MASS RATIO: He vs. N 1 atom He = 4 amu N = 14 amu 2 atoms 8 amu 28 amu 10 atoms 40 amu 140 amu 100 atoms 400 amu 1400 amu Mass ratio ( 2 : 7 ) is always the same!
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AVOGADRO’S NUMBER 1 carbon atom = 12.01 amu
?? atoms = grams of carbon ANSWER: x 1023 atoms! Avogadro’s number: number of atoms whose mass in grams = mass of one atom in amu
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AVOGADRO’S NUMBER We call this number of “things” one MOLE:
6.02 x 1023 “things” = 1 mole just like 12 “things” = 1 dozen
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“THINGS”: REPRESENTATIVE PARTICLES
1 mole = 6.02 x 1023 representative particles 1 mole carbon = 6.02x1023 atoms 1 mole CO2 = 6.02x1023 molecules 1 mole NaCl = 6.02x1023 formula units
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THE MOLE AND MOLAR MASS 1 atom of hydrogen = 1.01 amu
6.02x1023 atoms of H = 1.01 grams 1 mole of H = 1.01 grams usually written as: g/mole This number is called the MOLAR MASS of hydrogen.
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MOLAR MASS In textbook: gram atomic mass gram molecular mass
gram formula mass ALL mean the same – the mass of one mole of a substance: MOLAR MASS
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MOLAR MASS carbon: MM = 12.01 g/mole 12.01 g = 1 mole = 6.02x1023atoms
magnesium: MM = g/mole 24.34 g = 1 mole = 6.02x1023atoms 1 mole = same number of atoms = different number of grams
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MOLAR MASS What is the molar mass of sulfur? 32.07 g/mole
What is the molar mass of SO3? 80.07 g/mole What is the molar mass of NaCl? 58.44 g/mole
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AMADEO AVOGADRO
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