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List as many
Ex:
counting terms as  Pair = 2
you can.
 Dozen = 12
 Score = 20
A counting term is a  Gross = 144
word that
 Mole = 6.02 x 1023
represents a

specific number
CH 7 The Mole and
Chemical Compounds
Avagadro’s Number
The mole
Mole Conversions
Percent Composition
Empirical Formula
The mole – like a dozen
only bigger
Equal to the
number of
atoms in 12.0g
of carbon-12.

1 Mole = 6.02 x 1023
particles
Also known as:
Avagadro’s Number
After Italian physicist
Amadeo Avogadro
Chemistry particles
An atom
Na, Li, He
A molecule
O2 , H2O , CCl4
A formula unit
(this is what you call a
“molecule” of an ionic substance)
NaCl, MgO, H2SO4
Conversions
A conversion factor is a form of the
number 1. Multiplying by it only
changes the units.

Multiply using the conversion factor
with the units you WANT on the top.

How many eggs in 5 dozen?

How many score in 90 years?

How many atoms are there in 2.0
mol of sodium?

How many atoms in 3.5 mol of
sodium?

How many molecules are there in
2.5 mol of sulfur dioxide?

How many atoms are there in 2.5
mol of sulfur dioxide?
Label each of the following
atom, molecule, or formula unit (F.U.),
or ion
Sodium Metal: Na
 Oxygen gas: O2
 Water: H2O
 Sodium Chloride: NaCl
 Iron (III): Fe3+
 Phosphorus Trichloride: PCl3
 Methane: CH4

Solve on Whiteboard, show work

How many atoms are there in 0.02mol of
Iron?

How many atoms are there in 0.02mol of
Water?

How many moles are there in 9.03x 1024
molecules of water?
How many moles are there in 9.03x
1024 molecules of water?
“molecular weight”
“molar mass”
The mass of one mole of an element or
compound.
Determine the mass using the atomic mass
from the periodic table. (numerically equal to
atomic mass)
atomic weight
molar mass
Sodium
22.99 amu
22.99 g
Magnesium
24.30 amu
g
How to calculate molar mass
Use the atomic
mass from the
periodic table.
2. Add up the atomic
masses for each
element in the
compound.
NaCl =
22.99g + 35.45g
58.44 grams/mole
1.
Ex. H2O
2 Hydrogens x 1.0g
+
1 Oxygen
x 16.0g
18.0 grams/ mole
Find the molar mass of the
following compounds

CO2

LiF

Na2S

HCl

KClO
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What is the molar mass of
Sulfur Trioxide

S = 1 x 32.1
O = 3 x 16.0
80.1 g/mol
Find the molar mass of
Acetic Acid
HC2H3O2
What is the mass of 2 moles of acetic
acid?
Writing/abbrevieating:Mole
Mole
 mol
n

(don’t read this as “molecule”)
2.0 moles of Carbon = 24.02g
2.0 mol Carbon = 24.02g
2.0 n Carbon = 24.02g
Determine the molar mass
NH3
14+1+1+1 = 17 g/mol
What is the mass of
3 moles of NH3
3mol x 17 g/mol = 51g
Determine the mass of

1.75mol Uranium

0.7mol SF6
Determine the mass of
1.
2.
3.
4.
0.720 mol Be
2.40 mol N2
4.52x10-3 mol C20H42
5.08 n Calcium Nitrate
Find the number of moles in
1. 5.00g of Hydrogen gas (H2)
2. 11.0 g of methane (CH4)
3. 333g of Tin (II) Fluoride
Converting #Particles to Mass
1.
2.
Divide the number of particles by
Avagadro’s # to get moles.
Multiply the #moles by molar mass to
get grams
Find the mass of 2.44 x 1024 atoms of
Carbon.
Calculate the mass slates
path: Particles  Moles  Mass
5.3 x 1023 atoms of Molybdenum (Mo)
1.299 x 1026 ions of Nitrate (NO3-)
6.12 x 1014 formula units of Rhenium
Oxide (ReO2)
Calculate the # of Particles slates
path: Mass  Mole  Particles
How many atoms in 54.3g of Cobalt (Co) ?
How many molecules in 245g of Oxygen gas
(O2)?
How many molecules in 0.0923g Hydrgen
Fluoride gas (HF)?
Molar Volume of a gas
Molar volume of a gas
The volume of 1 mole of a gas
(any gas)
at Standard Temperature and Pressure
(STP) is 22.4 Liters.
[the volume of 45 water bottles]
The standard conditions (STP) are:


Temp: 0 C
Pressure: 1.0 atmosphere
Calculate the volume of the
following @ STP:

2.0 moles of
Oxygen

3.5 moles of
oxygen

3.5 moles of
Carbon Dioxide
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
In a 10.O gram Oreo
cookie, the cream has
a mass of 2.0 grams.
What is the %
composition (by
mass) of the cookie?
Calculate % Composition
*from lab data
1.
2.
3.
4.
Add the masses of each
element to find the total
mass.
Divide the mass of one
element by the total mass,
multiply by 100 (then add %
sign)
Repeat step 2, for each
element
Add up all the %s to make
sure they = 100%
An 8.2 gram piece of Mg combines
with 5.4 grams of Oxygen.
What is the % composition?
1.
Add the masses to find the total.
2.
Divide the mass of one element by the
total mass. Multiply by 100 (add %)
3.
Repeat for other elements.
4.
Do the %’s add to 100?
Calculate % composition
*from the chemical formula

What is the
percent
composition
of Propane,
C3H8 ?
1.
Assume you have 1 mole of the substance.
2.
Determine molecular mass of the substance.
3.
Divide the mass of one element by the
molecular mass. Multiply by 100. (add ‘%’)
4.
Repeat for other elements in the substance.
Do the %s add to 100?
5.
Determine the percent composition
Of water.

Warm Up

Determine the % Composition of MgCl2

If you have 100g of magnesium chloride
how many grams of magnesium are
there?

If you have 84g of magnesium chloride
how many grams of magnesium are
there?
Empirical Formulas:
The empirical formula may or may not
give the actual formula.
For any compound, its empirical formula
is the lowest whole number ratio of
elements.
Empirical Formula form
molecular formula
Compound
Chemical Formula
Empirical Formula
(lowest whole
number ratio)
Hydrogen
Peroxide
H2O2
HO
Glucose
C6H12O6
C? H? O?
Acetic Acid
C2H4O2
Ammonia
NH3
Empirical Formula

Use lab data to determine ratio of
elements.
Calculating empirical formula
*from lab data (% comp data)
The % composition is 20.1% Hydrogen and
79.9% Carbon.
Determine the empirical formula.
1. Assume 100g total (easy conversion from %)
So:
20.1g of Hydrogen
79.9g of Carbon
2. Determine the
number of moles
of each element.
Convert the grams
of each element
to a number of
moles.

20.1 g H /1.01 g/mole
_____ moles of
Hydrogen

79.9 g C / 12.01 g/mole
____moles of Carbon
C H
Subscripts must be
whole numbers.
3. Divide each
amount of moles by
the smallest
number.

C

H
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What is the empirical formula for
Oxalic Acid?
H2C2O4

Empirical formula is the lowest
whole number ratio of elements in a
compound.
A chemical compound has the
empirical formula CH2O
The molar mass of the compound is
180g/mol
What is the molecular formula?