01 Molar Mass.notebook
March 28, 2017
Quan es in
Chemical Reac ons
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01 Molar Mass.notebook
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Quan ta ve Analysis
Quan ta ve analysis involves the measurement of the
characteris cs or proper es of ma er using a number.
(e.g. the block has a mass of 3.25 kg)
In par cular we need to be able to "count" the atoms and
molecules that are involved in chemical reac ons.
Molecules are too small to count, but there are ways to
relate mass of a substance to the number of molecules
allowing us to easily count the number of par cles.
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01 Molar Mass.notebook
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Ra os in a Chemical Equa on
2H2 (g) + O2(g) ---> 2H2O(g)
the two gases must react in a ra o of H2 : O2 = 2:1
for gases at the same temperature and pressure equal
volumes of gas contain the same number of par cles
therefor we need only half the volume of oxygen to react
with all the hydrogen
for a small pop bo le that means:
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01 Molar Mass.notebook
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Demo: Hydrogen Rocket
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Test Tube
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2
3
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drops of Cu2+
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12
20
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drops of CO32-
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28
20
12
4
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01 Molar Mass.notebook
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01 Molar Mass.notebook
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Pb(NO3)2(aq) + 2KI(aq) ---> PbI2(s) + 2KNO3(aq)
Pb
NO
I
NO
I
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01 Molar Mass.notebook
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of particles in a Mole (6.02x10 23 particles). The number is
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23
6.02 x 1023
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01 Molar Mass.notebook
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Mass of Atoms
The mass of any atom is determined by the number of
protons and neutrons found in the atom.
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1.67x10-27kg = 1 amu
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A natural sample of an element contains a mixture of isotopes
of that atom. We use a weighted average to determine the
mass of an atom
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Cl
37
76%
Cl
24%
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01 Molar Mass.notebook
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Example 1
In any naturally occuring carbon sample will contain 98.9%
carbon-12 atoms and 1.1% carbon-13 atoms. What is the
average atomic mass of carbon?
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01 Molar Mass.notebook
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Molecular and Formula Unit Mass
The mass of a molecule (or a formula unit) is found by
adding up the masses of all of the individual atoms in
the molecule.
eg. water, H2O
H2O mass = 2(Hmass) + (Omass)
= 2 (1.01u) + (16.00u)
= 18.02 u
e.g. sodium sulfate, Na2SO4
Na2SO4 mass = 2(Namass) + (Smass) + 4(Omass)
= 2 (22.99u) + (32.07u) + 4(16.00u)
= 142.05 u
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Rela ng Mass to Number of Par cles
CH4(g) + H20(g) ---> 3H2(g) + CO(g)
par cles
molecular mass
dozens
moles
molar mass
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01 Molar Mass.notebook
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Molar Mass
molar mass is the mass in grams of 1 mole or 6.02 x 1023
en es of that substance
for an element the molar mass is equal to the atomic
mass expressed in grams/mole
Au
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for a compound the molar mass is the sum of the elements
in a compound each mul plied by their subscripts
Al2O3
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01 Molar Mass.notebook
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Determine the following Molar Masses:
(a) carbon dioxide, CO2
(b) iron(III) oxide, Fe2O3
(c) iron(III) chloride heptahydrate
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01 Molar Mass.notebook
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Calcula ons Involving Molar Mass
we can use the following rela onships to solve problems
involving moles
# of par cles
moles
mass
How many moles of sodium carbonate are in 25.6 g?
write the first term in the ra o so that contains both of
the units from the ques on
write the given quan ty and a variable in the next term of
the ra o
write a final term that contains a known rela onship for
the units involved
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01 Molar Mass.notebook
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Example 1
How many moles are in 10 grams of water?
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01 Molar Mass.notebook
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Example 2
A can of coke contains 40.0 g of sucrose. How many molecules
of sucrose in the can?
# of par cles = moles = mass
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Example 3
What mass of glucose (C6H12O6) is in a 1.0 L of human blood if a
litre typically contains 4.0 mmol of glucose?
# of par cles = moles = mass
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How many molecules are there in 24 grams of FeF3?
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How many grams are in 2.3 x 1024 atoms of silver?
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