1. Unit 06
The Mole Theory
Ch. 4 and 7

2. Dimensional Analysis ● just converting one thing to another
Problem 1: How many seconds are in a day? sec day What do we know? Let’s solve.
Conversion factors: the numerator and denominator are equal × ×
= 86,400 sec
1 day

3. 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
party

4. 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.

5. Mass of a Mole
Molar Mass- the mass of a mole of any element or compound (in grams)
Also called:
Formula mass – sum of the atomic masses of all the atoms in a formula of a compound

6. How to determine molar mass-
The atomic mass expressed in grams- rounded to whole number (ones place)
Examples:
C =
Cl =
O =
F =
12g
35g
16g
19g

7. How to determine molar mass-
For compounds- Add together all the atoms that make up the compound
Examples:
SO3 = 
1 S atom
3 O atoms
32g g g + 16g = 80g

8. How to determine molar mass-
What is the gram formula mass of ammonium carbonate (NH4) 2CO3?
Take inventory:
N × 14 = 28
H × 1 = 8
C × 12 = 12
O × 16 = 48
96g

9. Number of particles in a Mole
1 mole = 6.02 × representative particles
(also called Avogadro’s Number)
What is a representative particle? How the substance normally exists:
Atom- rep. particle for most elements
Molecule- rep. particle for covalent compounds and diatomic molecules “BrINCl HOF”
Formula unit- rep. particle for ionic compounds

10. 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 OR
6.02 × 1023 particles
6.02 × 1023 particles
1 mole

11. How to solve mole problems:
How many moles are in the number of molecules?
Sample problem: × 1023 atoms Mg
1. Determine known and unknown.
Known: × 1023 atoms Mg
Unknown: moles
2. Determine the conversion factor(s) needed.
3. Multiply the known by the appropriate conversion factor(s) so units cancel.
4. Calculate answer
2.08 × 10-1 moles or moles
1 mole
6.02 × 1023 particles
6.02 × 1023 particles
1 mole or
1.25 × 1023 atoms Mg
1 mole
6.02 × 1023 atoms

12. The Mole and Avogadro’s Number
1.) How many molecules are in 2.0 moles?
6.02  1023
molecules
1 mole
2.0 mole
= 1.20  1024
molecules

13. The Mole and Avogadro’s Number
1.) How many moles are in
6.02 × 1023 particles?
1 mole
6.02 × 1023 particles
6.02 × 1023 particles
= 1 mole

14. Mole – Mass Relationship
Use the following conversion factors:
1mole or molar mass
molar mass mole
(we have to calculate the molar mass of the substance)

15. Moles  Grams Ex.) How many grams are in 9.45 moles of N2O3?
Known: 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 x 76g = g N2O3
mole

16. 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 = mole Fe2O3 g

17. Molar Conversion Examples
Find the mass of 2.1  1024 molecules of NaHCO3.
2.1  1024
molecules
1 mole
6.02  1023
molecules
84 g
1 mole
= g NaHCO3

18. 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 L
22.4 L 1 mole

19. Volume  Moles
Ex.) Determine the volume, in liters, if 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 L = L SO2
mole

20. All the conversion factors you need to know!
Representative Particles
6.02 × 1023 particles
1 mole
1 mole
6.02 × 1023 particles OR
Mass
1 Mole OR Molar Mass
Molar mass Mole
Volume
1 mole OR L
22.4 L 1 mole

21. Your clothing labels have Percent Composition.

22. 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 × 100
molar mass (g) of compound

23. 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
% C = X 100
% C = 81.8 or 82%

24. Now, calculate the percent hydrogen in C3H8 %H = 8g X 100
%H = X 100
%H = 18.2 or 18%