1. The Mole – A measurement of matter
10-1 Notes
The Mole – A measurement of matter

2. Measuring Matter Chemistry is a quantitative science
We will be analyzing the composition of samples of matter and perform chemical calculations that relate quantities of reactants in a chemical reaction to the quantities of products
Ex: How many grams of H2 and N2 must be combined to make 200 grams of fertilizer (NH3)?
1st we must find a way to measure the amount of matter we have.
By counting how much matter, finding the mass, or finding the volume of matter

3. What is a Mole?
Review: Matter is composed of atoms, molecules, and ions
Particles that are much to small to count
We use a unit called a mole (mol) to count particles of matter
A mole of a substance is 6.02 x representative particles of that substance
Known as Avogadro’s Constant
see table 10.1
Ex. 1 mole of Na = 6.02 x 1023 atoms of Na

4. Mole Conversions How many moles of Mg are in 1.25 x 1023 atoms of Mg?
Use this conversion: 1 mol = 6.02 x 1023
Answer: mol Mg
Practice Problem # 3
How many atoms are in 2.12 mol of propane?
Conversion – moles  molecules  atoms
Answer: 1.40 x 1025 atoms
Practice Problem #5

5. The Mass of a Mole
Review: The atomic mass of an element is expressed in atomic mass units (amu).
The atomic masses are relative values based on the most common isotope of carbon.
The atomic mass of C is 12 amu which is 12 times heavier then H (mass of 1 amu)
Results in a constant 12:1 ratio
Therefore, 12 grams of C and 1 gram of H must contain the same number of atoms

6. The Mass of a Mole
The atomic mass of an element expressed in grams is the mass of a mole of the element
Ex. The molar mass of Carbon is 12 grams
Because 1 mole of any element contains x 1023 atoms, the number of atoms in 12 grams of Carbon = the number of atoms in 16 grams of Oxygen
Molar Mass is the mass of 1 mol of atoms of any element

7. The Mass of a Mole Step 1: Determine the formula for the compound
Step 2: Find the number of grams of each element in one mole of the compound
Step 3: Add the masses of the elements in the compound
This method is used for any type of compound

8. The Mass of a Mole Find the mass of 1 mol of Sulfur trioxide
SO3 = 1 sulfur atom and 3 oxygen atoms
1 atom sulfur x 32.1 amu = 32.1 amu
3 atoms oxygen x 16.0 amu (per oxygen) = amu
32.1 amu amu = 80.1 amu for Sulfur trioxide
Substitute grams for amu.
1 mol of SO3 has a mass of 80.1 grams
Practice Problem # 7

9. Mole-Mass and Mole-Volume Relationships
10-2 Notes
Mole-Mass and Mole-Volume Relationships

10. Mole-Mass Relationship
Use the molar mass of an element or compound to convert between the mass of a substance and the moles of that substance.
Mass (grams) = number of moles x (mass / 1 mole)
Ex. The molar mass of NaCl is 58.5 grams. What is the molar mass of 3 moles of NaCl?
3.00 mol NaCl x 58.5g/1 mol = 176 g
Sample problem 10.5

11. Mole-Mass Relationship
Suppose in the lab you were able to obtain grams of Na2SO4.
How many moles is this?
moles = mass x (1mol/mass)
moles of Na2SO4 = 10.0 grams x (1 mol/142.1 g)
moles of Na2SO4 = 7.04 x 10-2
Sample problem 10.6

12. Mole-Volume Relationship
The volumes of one mole of different solid and liquid substances are not the same
fig on page 295
The volumes of gases are much more predictable
In 1811 Avogadro stated that equal volumes of gases at the same temperature and pressure contain equal number of particles
Even though the particles that make up different gases are not the same size, they take up relatively the same space

13. Mole-Volume Relationship
The volume of a gas will vary depending on the temperature or the pressure
Increase in pressure = decrease in volume
The volume of a gas is usually measured at standard temperature and pressure (STP)
STP is at O oC and at a pressure of kPa or 1 atmosphere (atm)
At STP 1 mol of any gas occupies a volume of L
This is referred to as molar volume

14. Mole-Volume Relationship
To calculate volume of a gas at STP:
Volume of gas = moles of gas x (22.4 L/1 mol)
Determine the volume (Liters) of 0.60 mol SO2 at STP
You can also calculate molar mass from Density.
The density of a gas at STP is 22.4L/mol
Molar mass = STP x molar STP
Determine the mass of a compound that has a density of g/L at STP

15. Percent Composition and Chemical Formulas
10-3 Notes
Percent Composition
and Chemical Formulas

16. Percent Composition
The % composition of a compound consists of a % value for each different element in the compound
% composition from mass data
The % mass of an element is the # of grams of the element divided by the mass in grams of the compound, multiplied by 100
% mass of element =
mass of element x 100
mass of compound
Sample problem 10.9

17. Percent Composition % Composition from the Chemical Formula % mass =
Mass of element in 1 mol compound x 100
Molar mass of compound
Sample Problem 10.10

18. % Composition as a Conversion Factor
You can use % comp. to calculate the number of grams of any element in a specific mass of a compound
Multiply the mass of the compound by a conversion factor based on the % comp of the element in the compound.
Sample problem:
In we found in propane, the % comp of Carbon was 81.8%. What would the mass of Carbon be in an 82.0 g sample?

19. Empirical Formulas
The % comp. of any compound is the data we use to calculate the basic ratio of elements contained in a compound
The basic ratio that gives the lowest whole-number ratio of the atoms of the elements in a compound is called the empirical formula
An empirical formula may or may not be the same as a molecular formula
Example: The molecular formula for hydrogen peroxide is H2O2 the empirical formula is HO
Sample problem 10.11

20. Molecular Formulas
The molecular formula of a compound is either the same as its experimentally determined empirical formula, or it is a simple whole-number multiple of its empirical formula
To find the molecular formula you must first know the molar mass of the compound.
Sample Problem 10.12