The Mole Theory

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?
• Lets 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 12 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 16g 16g 16g
80g
8
How to determine molar mass-

• What is the gram formula mass of ammonium
  carbonate (NH4) 2CO3?
• Take inventory
• N- 2 14 28
• H- 8 1 8
• C- 1 12 12
• O- 3 16 48
• 96g

9
Number of particles in a Mole
1 mole 6.02 10 23 representative particles
(also called Avogadros 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

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 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. 3. Multiply the
known by the appropriate conversion factor(s) so
units cancel.
4. Calculate answer 2.08 10-1 moles
or .208 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 Avogadros 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 Avogadros 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 1 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 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 x 76g 718.2 g N2O3
• 1 1 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 0.576 mole Fe2O3
• 1 160g

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
293.02 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)
• 0C 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

19
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

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 1 Mole

• Volume

1 mole OR 22.4 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
• 44g
• C .818181 X 100
• C 81.8 or 82

24

• Now, calculate the percent hydrogen in C3H8
• H 8g X 100
• 44g
• H .181818 X 100
• H 18.2 or 18