1. The Mole: A measurement of Matter
Chapter 10
Chemical Quantities
Section 10.1
The Mole: A measurement of Matter

2. What is a Mole? 6.02 X 1023 is called Avogadro’s number
A mole (mol) of a substance is 6.02 X 1023 representative particles of that substance.
Usually atoms or molecules.
6.02 X 1023 is called Avogadro’s number

3. Converting Number of Particles to Moles
Av.
number
Molecules or atoms
e.g.
How many moles of magnesium in 1.25 X atoms of magnesium
= mol Mg
Page 291: #3 & 4
Moles - Particles

4. Converting Moles to Number of Particles
e.g. How many atoms are in 2.12 mol of propane (C3H8)?
Number of atoms = 2.12 x 6.02 x x 11
= 1.4 x atoms
Page: 292 #5 & 6

5. The mass of a Mole of an Element
The mass of a mole of an element is its molar mass.
How can you calculate the molar mass of a compound?
To calculate the molar mass of a compound:
1. Find the number of grams of each element.
2. Add the masses of the elements in the compound.
e.g. what is the molar mass of calcium oxide?
Chemical formula = CaO,
Ca = 40, O = 16
Molar mass = = 56g
Page: 296, #7 & 8

6. Moles – Atoms Number of Moles Avogadro’s Number If atoms Atoms or
Molecules
Particles
Number of Moles
Avogadro’s
Number
If atoms
Multiplies by number of atoms

7. Section 10.2
Mole – Mass
&
Mole – Volume
Relationships

8. Converting Mass to Moles
e.g. How many moles of iron(III) oxide are contained
in 92.2g of pure Fe2O3?
Mass = 92.2g
Molar mass = 2x x16 = 159.6g/mol
Number of moles = 92.2/159.6 = mol Fe2O3
Page: 299, # 18 & 19
Moles - Mass

9. Converting Moles to Mass
Mass = number of Moles x molar mass
e.g. What is the mass of 9.45 mol of aluminum oxide?
Chemical Formula = Al2O3
Number of moles = 9.45 mol
Molar mass = 2x27 + 3x16 = 102g Al2O3
Mass = x 102 =964g Al2O3
Page: 298, # 16 & 17

10. The volume of a Mole of an Element
The volume of a mole of an element is called molar volume
The molar volume of a gas at STP is 22.4 L
Standard Temperature and Pressure
To calculate the volume of a gas at STP:
Volume of gas = Number of Moles x 22.4
e.g. Determine the volume of 0.6 mol sulfur dioxide gas at STP.
Volume of SO2 = 0.6 x 22.4 = 13.4 L SO2
Page: 301, #20 & 21
Moles - Volume

11. Calculating Molar Mass from Density
Molar mass = density at STP x molar volume at STP
e.g. The density of a gaseous compound carbon and oxygen is found
to be 1.964g/L at STP. What is the molar mass of the compound?
Molar mass = x 22.4 = 44g/mol
Page: 302, #22 & 23
Moles - Density

12. Moles – Mass
Mass
Number of Moles
Molar

13. Moles – Volume
Volume
Number of Moles
22.4

14. Moles – Density
Molar mass
Density
22.4

15. Section 10.3
Percent Composition and Chemical Formulas

16. The percent composition is the relative amounts of the elements in a compound.
The percent by mass of an element in a compound is the number of grams of the element divided by the mass in grams of the compound, multiplied by 100
Calculating Percent Composition from Mass Data
e.g. When a 13.6 g sample of a compound containing only magnesium and oxygen.
5.4 g of oxygen is obtained. What is the percent composition of this compound?
Mass of compound = 13.6 g
Mass of oxygen = 5.4 g
Mass of magnesium = 13.6 – 5.4 = 8.2 g
Page 306, # 32 & 33

17. Calculating Percent Composition from the Chemical Formula
e.g. Propane (C3H8) is one of the compounds obtained from petroleum.
Calculate the percent composition of propane.
Mass of C in C3H8 = 36 g
Mass of H in C3H8 = 8.08 g
Molar mass of C3H8 = g/mol
Page: 307, # 34 & 35

18. Empirical Formula
The empirical formula of a compound shows the smallest whole-number ratio of the atoms in the compound.
It shows the kinds and lowest relative count of atoms or moles of atoms in molecules or a compound.
An empirical formula may or may not be the same as a molecular formula. For example, the lowest ratio of hydrogen to oxygen in hydrogen peroxide is 1:1
So the empirical formula of hydrogen peroxide is HO
The actual molecular formula of hydrogen peroxide has twice the number of atoms as the empirical formula.
The molecular formula is (HO) x 2 or H2O2
Notice that the ratio of hydrogen to oxygen is still the same.
The molecular formula tells the actual number of each kind of atom present in a molecule of the compound.
For carbon dioxide, the empirical and molecular formulas are the same – CO2

19. e.g. A compound is analyzed and found to contain 25.9% nitrogen and
74.1% oxygen. What is the empirical formula of the compound?
25.9% N % O
Step 1. Assume that you have 100 g of the compound,
25.9 g g
Step 2. Divide each by its atomic mass.
1.85 mol
4.63 mol
Step 3. Divide each by the smallest number of moles.
1.85
4.63
1.85
1.85 1
2.5
Multiply all by 2
The empirical formula is N2O5
Page: 310, # 36 & 37

20. Molecular Formula
is the same as the empirical formula or it is a simple whole-number multiple of its empirical
Once you determined the empirical formula of a compound, you can determine its molecular formula, but you must know the compound’s molar mass and empirical formula mass.
e.g. Calculate the molecular formula of a compound whose molar mass
is 60 g/mol and empirical formula is CH4N
Empirical formula = CH4N
Molar mass = 60 g/mol
Molecular formula = C?H?N?
Step 1. Calculate the empirical formula mass
Empirical formula mass = 1x12 + 4x x14 = g/mol
Step 2. Divide the molar mass by the empirical formula mass
60 = 2
30.04
Step 3. Multiply the formula subscripts by this value (factor)
Molecular formula = 2 x CH4N = C2H8N2
Page: 312, # 38 & 39
Table page: 311