Mole, Molar Mass, Conversions, and % Composition
Mole:
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6.02 x 1023 particles (atoms, molecules, etc.)
Abbreviation: mol
Also known as Avogadro’s #
SI unit used to measure the amount of a substance
The # of carbon atoms in exactly 12g of pure carbon-12
Particle (atoms, molecules, ions, etc.) to Mole Conversions & Mole to Particle Conversions
Conversion factors:
6.02 x 1023 particles
1 mole
=
______1 mole_____
6.02 x 1023 particles
number of moles x 6.02 x 1023 particles = number of particles
1 mole
number of particles x _____1mole______ = number of moles
6.02 x 1023 particles
Example:
3.50 moles sucrose x 6.02 x 1023 molecules sucrose = 2.11 x 1024 molecules sucrose
1 mole sucrose
2.11 x 1024 molecules sucrose x _________1 mole_________ = 3.50 moles sucrose
6.02 x 1023 molecules sucrose
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`The molecular formula of a compound tells us the mole ratio of its component
atoms
Example: CCl2F2
This tells us there is 1 mole of C atoms and 2 moles Cl atoms and 2 moles F atoms in
every mole of CCl2F2
Molar Mass:
 The mass in grams of one mole of any pure substance
 For an element it is equal to its average atomic mass and has units g/mol
 Example: Iron has molar mass of 55.845 g/mol
i.e. 1 mole of iron has a mass of 55.845g
Mass to Mole Conversions and Mole to Mass Conversions
Conversion Factors:
grams
mole
=
mole
grams
Number of moles x mass in grams = mass in grams
1 mole
mass in grams x number of moles = # of moles
mass in grams
Example:
3.00 moles Cu x 63.546 g Cu = 191g Cu
1 mole Cu
191 g Cu x 1 mole Cu = 3 moles Cu
63.546 g Cu
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For a compound it is equal to the sum of the average atomic mass of all its particles
Example: K2CrO4 is equal to
2 moles K x 39.10g K = 78.20 g K
1 mole K
1 mole Cr x 52.00 g Cr = 52.00 g Cr
1 mole Cr
4 moles O x 16.00g O = 63.00 g O
1 mole O
Molar Mass of K2CrO4 = 78.20 g K + 52.00 g Cr + 63.00 g O = 194.20g K2CrO4
Mass to Particle Conversions and Particle to Mass Conversions
 To convert mass to particles - convert from mass to moles then from moles to
particles (See above)
 To convert from particles to mass – convert from particles to moles then from moles
to mass (See above)
% Composition or percent by mass (element)
 Percent by mass = mass of element in 1 mole of compound x 100%
Molar mass of compound
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Percent composition is the mass percents of the elements present
Example: HNO3
1 mole of H, 1 mole of N, and 3 moles of O per mole of HNO3
First find molar mass of each element:
1 mole H x 1.01 g H = 1.01 g H
1 mole H
1 mole N x 14.01 g N = 14.01 g N
1 mole N
3 moles O x 16.00 g O = 48 g O
1 mole O
Molar mass: 1.01g + 14.01g + 48g = 63.02g HNO3
% mass H = 1.01 g/mol H x 100% = 1.6% H
63.02 g HNO3
% mass N = 14.01 g N x 100% = 22.2% N
63.02 g HNO3
% mass O =
48.00g O x 100% = 76.1% O
63.02 g HNO3