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Lecture 23

CHEM-C 101 Lecture Notes - Lecture 23: Molar Mass, Carbon-12, Unified Atomic Mass UnitPremium

1 pages106 viewsFall 2018

Course Code
CHEM-C 101
Kimberly Arnold

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Chapter 9: Stoichiometry and the Mole
The Mole
Relates the number of atoms or molecules to grams
Abbreviation is “mol”
Individual atoms cannot be counted because of their extremely small size
o Conversions are similar to “12 items=1 dozen”
1 mol= 6.022 x 1023 items
o This number is very large, but the atoms or molecules are very small
o Examples to show how small a mole is:
1 mole of sugar molecules can fit in your hand
1 mole of water molecules is barely a sip of water
If you counted all the grains of sand on earth, you wouldn’t get to 1 mole
Avogardo’s Number
Number of atoms/molecules in 1 mole
6.022 x 1023
Conversion factors
o 1 mole of something or
The definition of the mole is based on the isotope carbon-12
o Exactly 12 grams of carbon-12 contains exactly one mole of carbon-12 atoms
o 12 grams C-12=1 mole C-12
Molar Mass
The molar mass of an atom is the mass of one mole of the atom
To determine the molar mass, you replace the units of “amu” with “grams” to find the
mass of 1 mole
For example, a hydrogen atoms atomic mass is 1.0079 amu, so 1 mole of hydrogen =
1.0079 grams of hydrogen
This method works for all the elements
6.022 x 1023 of something
6.022 x 1023 of something
1 mole of something
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