Masses and moles
Not that kind of mole
Re-mem-mem
Re-mem-mem-member…
19
39.0983
K
Potassium
Average atomic
mass, in amu/atom
Re-mem-mem
Re-mem-mem-member…
19
39.0983
K
Potassium
Assume the most common isotope has
39 p+n (19p and 20n)—but there are
some heavier ones.
And now, for something completely
different.
• Def:
1 mole=6.02 x
Not that kind
of mole
23
10
particles
As a conversion factor
• 2.7 moles Ar = _?_atoms Ar
• 1.5 x 1021 molecules H2O=__?__moles H2O
.
As a conversion factor
• 2.7 moles Ar = _?_atoms Ar
2.7 moles Ar x 6.02 x 1023 atoms Ar =
1 mole Ar
• 1.5 x 1021 molecules H2O=__?__moles H2O
1.5 x 1021 molecules H2O x 1mole H2O =
6.02 x 1023molecules H2O
As a conversion factor
• 2.7 moles Ar = _?_atoms Ar
2.7 moles Ar x 6.02 x 1023 atoms Ar =
1 mole Ar
1.6 x 1024
atoms Ar
• 1.5 x 1021 molecules H2O=__?__moles H2O
.0025
1.5 x 1021 molecules H2O x 1mole H2O = moles H20
6.02 x 1023molecules H2O
6.02 x 1023
6.02 x 1023
• Avogadro’s number.
• Amadeo Avogadro.
• He suggested that there is a number.
• The number is larger than he expected.
The greatest conversion of all time!
1 amu X 6.02 x 1023 = 1 gram
atom X 6.02 x 1023
mole
• Avogadro’s number is also the conversion
from amu’s to grams.
• Both sets of units define the mole.
What is the mass?
• .0582 mol Ni
• 12.0 mol Ne
• 4.80 x 10 25 atoms Xe
• 1.24 x 10 21 atoms Au
What is the mass?
• .0582 mol Ni
• 12.0 mol Ne
• 4.80 x 10 25 atoms Xe
• 1.24 x 10 21 atoms Au
Convert
to moles
first!
What is the mass?
• .0582 mol Ni
3.42 g Ni
• 12.0 mol Ne
242 g Ne
• 4.80 x 10 25 atoms Xe
10500 g Xe
• 1.24 x 10 21 atoms Au
.406 g Au
What is the mass?
• 2.4 mol He
• 9.03 x 10 23 atoms K
How many moles?
• 18.3 g Sr
• 4.8 g Ar
• 4.03 x 10 23 formula units of iron (III) oxide
• 7.24 x 10 21 molecules sulfur hexaflouride
How many moles?
• 18.3 g Sr
.209 mol Sr
• 4.8 g Ar
.12 mol Ar
• 4.03 x 10 23 formula units of iron (III) oxide
.669 mol Fe2O3
• 7.24 x 10 21 molecules sulfur hexaflouride
.012 mol SF6
How many moles?
• .130 g Ag
• 1.42 x 10 24 molecules nitrogen trichloride
Pop quiz
• If 1 mole of hydrogen atoms (H) has a
mass of 1.0078 g, what is the mass of 1
mole of hydrogen molecules (H2)?
Pop quiz
• If 1 mole of hydrogen atoms (H) has a
mass of 1.0078 g, what is the mass of 1
mole of hydrogen molecules (H2)?
• I hope you answered “Twice that mass.”,
or 2.0156 g
Formula masses
• If I give you a formula, you add the
masses of the atoms represented to get
the formula mass.
• The units are grams/mole
What is the formula mass of…
•
•
•
•
•
LiCl
BaF2
K2SO3
Fe2(Cr2O7)3
Na2HPO4 • 7H2O
What is the formula mass of…
•
•
•
•
•
Gold (I) fluoride
Lithium oxide
Cobalt (II) cyanide
dinitrogen trisulfide
tetraphosphorus hexoxide
PS
• The subscripts in a formula can be read:
K2SO3
There are two
There are two
potassium atoms or moles of potassium
in a formula unit
in a mole of
of potassium
potassium sulfite
sulfite
PS
• The standard molar volume for a gas is:
22.4L/mol
22.4L/mol
at STP
STP =standard temperature and pressure
= 273k, 1.00 atm
PS
22.4 L
is about
Mole conversions
Mole conversions
Mass
Moles
Mole conversions
Mass
Moles
Use the formula mass
Mole conversions
Mass
Moles
FM in grams = 1 mole
Mole conversions
Particles
Moles
Mole conversions
Particles
Moles
Use Avogadro’s number
Mole conversions
Particles
6.02 x 10
Moles
23
particles = 1 mole
Mole conversions
Volume
of a gas
at STP
Moles
Mole conversions
Volume
of a gas
at STP
Moles
Use the molar volume
Mole conversions
Volume
of a gas
at STP
Moles
22.4 L gas at STP = 1 mole
Mole conversions
Particles
Use
Avogadro’s
number
Use the
molar
volume
Volume of a
gas at STP
Moles
Use the
formula
mass
Mass
Styrene: an organic molecule, C8H8
1. What is the molecular weight of styrene?
2. What is the empirical formula of styrene?
3. How much does 1.000 mole of styrene
weigh?
4. How much does 1.54 pmole of styrene
weigh?
5. How much many moles in 9.67 kg of
styrene?
6. How many moles in 84.6 mg of styrene?
Styrene: an organic molecule, C8H8
1. What is the mass % of C in styrene?
2. What is the mass % of H in styrene?
3. An unknown material is recovered from
the Delaware River. Results from
analysis of it are Carbon 92.26%
Hydrogen7.74% Is it styrene?
4. The molecular weight of this compound is
78.11 grams per mole. What is its
molecular formula?