1. THE MOLE Unit 2: Quantities in Chemical Reactions
SCH3U
Miss Richardson
THE MOLE Unit 2: Quantities in Chemical Reactions

2. How many are there? 52cards = 1 deck 24 bottles = 1 case
2 shoes = 1 pair
12 eggs = 1 dozen
52cards = 1 deck
24 bottles = 1 case

3. How many (atoms) are there?
6.022 x 1023 carbon atoms = 1 mole

4. Amedeo Avogadro The mass of a single atom is incredibly small.
determined that any quantity of matter must contain an enormous number of atoms, ions, molecules, etc.
he showed that 12.01g of carbon contains 6.02 x 1023 atoms
Why is 12.01g a significant quantity?

5. Amedeo Avogadro Further investigations showed consistency:
A sample of NaCl has an average atomic mass of amu ( )
There are x 1023 molecules in g of NaCl

6. Avogadro’s Number
The quantity x 1023 is known as Avogadro’s number (NA) and is equal to 1 mole of a substance.
Eg: 1 pair of eggs = 2 eggs
1 dozen eggs = 12 eggs
1 mole of eggs = x eggs

7. Counting in Chemistry monatomic elements = atoms eg: Fe(s), S(s)
diatomic particles = molecules
eg: O2(g), F2(g), Cl2(l)
molecular compounds = molecules
eg: H2O(l), SO2(g)
ionic compounds = formula units
eg: NaCl(s), LiOH(g)

8. The Mole
The number of moles of a substance can be determined using this formula:
Where: n = number of moles.
N = number of particles
NA = Avogadro’s Constant = x 1023

9. Finding Number of Particles
Example:
An airbag contains 3.65 mol of hydrazine (N2H4(l))
How many molecules are there?
N = n x NA
N = 3.65 mol x x 1023 molecules
1 mol
= x 1024 molecules
= x 1024 molecules

10. Finding Number of Particles
Example:
An airbag contains 3.65 mol of hydrazine (N2H4(l))
How many molecules are there?
2.20 x 1024 molecules
How many atoms are there?
x 1024 molecules x 6 atoms
1 molecule
= x 1025 atoms
= x 1025 atoms

11. Molar Mass
When testing a product, chemists need to be sure the correct number of molecules (or moles of molecules) of the active ingredient are present.
To do this, we need a way to relate mass of a substance to the number of particles present.
molar mass = mass of 1 mole (or x particles) of any substance.

12. Calculating Molar Mass
molar mass = mass of 1 mole (or x particles) of any substance.
Where: m = mass of a substance (g)
n = #of moles of a substance (mol)
M = molar mass (g/mol)

13. Molar Mass - Example
What is the molar mass (M) of magnesium chloride, MgCl2?
Step 1: Find atomic masses on periodic table
MMg = g/mol MCl = g/mol
Step 2: Add atomic masses, accounting for number of each atom
MMgCl2 = MMg + MCl2
= (2x35.46) = g/mol

14. Particles, Mass and Moles