Unit 06
The Mole Theory
Ch. 4 and 7
Dimensional Analysis
● just converting one thing to another
Problem 1:
How many seconds are in a day?
sec
day
What do we know?
Conversion factors: the numerator and denominator are equal
Let’s solve.
×
×
= 86,400 sec
1 day
Dimensional Analysis
Problem 2:
You're throwing a pizza party for 15 and figure each person
might eat 4 slices. How much is the pizza going to cost you?
You call up the pizza place and learn that each pizza will cost
you $14.78 and will be cut into 12 slices. You tell them you'll
call back. How much money is the pizza going to cost you,
which in math terms is: cost (in dollars) per party, or just
$/party
14.78 x 4 x 15 = $73.90
12
party
How do you measure matter?
- Counting (dozen, 3/$1, 6 pack)
- Mass ( 1 lb, 4 oz, 57g)
- Volume (liter, gallon, pint,
quart)
In chemistry- this is all measured by a
measuring unit called the mole.
Mass of a Mole
Molar Mass- the mass of a mole of any
element or compound (in grams)
o Also called:
o
oFormula mass – sum of the atomic masses of
all the atoms in a formula of a compound
How to determine molar mass The
atomic mass expressed in gramsrounded to whole number (ones place)
 Examples:
 C = 12g
 Cl = 35g
 O = 16g
 F = 19g
How to determine molar massFor compounds- Add together all the
atoms that make up the compound
 Examples:
• SO3 =


1 S atom
32g
3 O atoms
+
16g + 16g + 16g
=
80g
How to determine molar massWhat is the gram formula mass of
ammonium carbonate (NH4) 2CO3?
 Take inventory:

◦
◦
◦
◦
NHCO-
2 × 14 = 28
8 × 1 = 8
1 × 12 = 12
3 × 16 = 48
96g
Number of particles in a Mole
1 mole = 6.02 × 10 23 representative particles
(also called Avogadro’s Number)
What is a representative particle?
How the substance normally exists:
1. Atom- rep. particle for most elements
2. Molecule- rep. particle for covalent
compounds and diatomic molecules
“BrINCl HOF”
3. Formula unit- rep. particle for ionic
compounds
Converting from moles –› particles
Analogy:
1 dozen = 12 eggs
Conversion Factors:
1 dozen or 12 eggs
12 eggs
1 dozen
For moles and particles:
1 mole = 6.02 × 1023 rep particles–
therefore
Conversion Factors
1 mole
6.02 × 1023 particles
23 particles
6.02
×
10
OR
1 mole
How to solve mole problems:
How many moles are in the number of molecules?
Sample problem: 1.25 × 1023 atoms Mg
1. Determine known and unknown.
Known: 1.25 × 1023 atoms Mg
Unknown: moles
2. Determine the conversion factor(s) needed.
1 mole
6.02 × 1023 particles
or
6.02 × 1023 particles
1 mole
3. Multiply the known by the appropriate conversion
factor(s) so units cancel.
1.25 × 1023 atoms Mg 1 mole
6.02 × 1023 atoms
4. Calculate answer
2.08 × 10-1 moles or .208 moles
The Mole and Avogadro’s Number
1.) How many molecules are in 2.0
moles?
6.02  1023
2.0 mole molecules
1 mole
= 1.20  1024
molecules
The Mole and Avogadro’s Number
1.) How many moles are in
6.02 × 1023 particles?
6.02 × 1023 particles
1 mole
6.02 × 1023 particles
= 1 mole
Mole – Mass Relationship

Use the following conversion factors:
1mole
or
molar mass
molar mass
1 mole
(we have to calculate the molar mass of the substance)
Moles  Grams
Ex.) How many grams are in 9.45 moles of N2O3?
Known: 9.45 moles of N2O3
Unknown: mass (grams) of N2O3
Step 1: calculate the molar mass of N2O3
N = 2 x 14 = 28
O = 3 x 16 = 48
76g
Step 2: solve
9.45 moles
1
x 76g
=
1 mole
718.2 g N2O3
Mass  Moles

Ex.) Find the number of moles in 92.2g of
Fe2O3?


Known: mass of Fe2O3 is 92.2g
Unknown: moles of Fe2O3

Step 1: Find the molar mass of Fe2O3
Fe = 2 x 56 = 112
O = 3 x 16 = 48
160g

Step 2: Solve
92.2g x 1 mole = 0.576 mole Fe2O3
1
160g
Molar Conversion Examples
the mass of 2.1  1024
molecules of NaHCO3.
 Find
2.1  1024
molecules
1 mole
84 g
6.02  1023 1 mole
molecules
= 293.02 g NaHCO3
Volume of a Mole of Gas
The Volume of a gas varies with a change
in temperature or pressure.
 Measured at standard temperature
and pressure (STP)

 0°C at 1 atmosphere (atm)

1 mole of any gas occupies a volume of
22.4L
Conversion Factors:
1mole
OR
22.4 L
22.4 L
1 mole
Volume  Moles

Ex.) Determine the volume, in liters, if 0.60
mole of SO2 gas at STP.
known: 0.60 mole
unknown: volume
Start with the known and then use the correct
conversion factor to solve for the unknown.
0.60 mole x 22.4 L = 13.44 L SO2
1
1 mole

All the conversion factors you need
to know!

Representative Particles
1 mole
6.02 × 1023 particles

Mass
1 Mole
Molar mass

OR
6.02 × 1023 particles
1 mole
OR
Molar Mass
1 Mole
Volume
1 mole
22.4 L
OR
22.4 L
1 mole
Your clothing labels have
Percent Composition.
Percent Composition

The percent by mass of each element in a
compound

Information needed:
◦ Formula of the compound
◦ Mass of the elements and the compound
% mass = mass grams of element
molar mass (g) of compound
× 100
Calculating Percent Composition

Calculate the percent carbon in C3H8
- Find the molar mass
C = 3 x 12 = 36g
H = 8 x 1 = 8g
44g

% C = mass(g) of carbon X 100
mass of C3H8
% C = 36g X 100
44g
% C = .818181 X 100
% C = 81.8 or 82%

Now, calculate the percent hydrogen in C3H8
%H = 8g X 100
44g
%H = .181818 X 100
%H = 18.2 or 18%