This document discusses quantitative chemistry concepts including the mole, Avogadro's constant, molar mass, and using moles to calculate the number of particles and mass of substances. Some key points covered are: - A mole is a unit used to count fundamental particles and represents 6.02x1023 particles. - The mole allows converting between large numbers of particles and more manageable units like grams. - Molar mass relates the mass of a sample of a substance to the number of moles it contains. - Problems use molar mass to calculate moles, particles, or mass given any two of those quantities.

1. IB Chemistry Power Points
Topic 1
Quantitative Chemistry
Lecture 1
www.pedagogics.ca
The Mole and Avogadro’s Constant

2. the Mole

3. A mole is a unit of quantity.
A mole is 6.02 x 1023 things.
6.02 x 1023 is known as Avogadro’s constant (NA)
÷ 6.02 x 1023
Number of
atoms,
molecules or
fundamental
units
Number of
moles (mol)
× 6.02 x 1023

4. The Mole
Consider one
molecule of water
How many molecules in
2000 cm3 of water?
6.7 x 1025 molecules

5. The Mole
6.7 x 1025 molecules is not a manageable
number. Consider:
We count eggs by the dozen
We measure long periods of time in
centuries.
We measure long distances in our
universe using light years.

6. The Mole
There are many ways of measuring large
quantities that utilize large units. The mole
is one such unit.
The mole is the SI unit for chemical
quantity used to count the particles in a
sample of pure substance.
One mole = 6.02x1023 particles.
“One mole of anything = 6.02x1023 units of that thing”

7. The Mole
How many
molecules of water
in 2000 cm3?
6.7 x 1025 molecules
Or 111 mol meaning 111 moles of water
molecules. This is a much more manageable
number.

8. How many atoms are in 0.065 mol of copper? 3.9 x 1022
How many molecules are in 0.065 mol of CO2? 3.9 x 1022
How many formula units are in 0.065 mol of NaCl? 3.9 x 1022
How many moles is 9.03 x 1023 atoms of copper? 1.5
How many moles is 9.03 x 1023 molecules of CO2? 1.5
How many moles is 9.03 x 1023 formula units of NaCl? 1.5

9. How many oxygen atoms are in 1.4 x 10-7 mol of oxygen gas (O2)?
(1.4 x 10-7) × NA = 8.428 x 1016 molecules of O2
2 atoms of oxygen per molecule so
final answer = 1.7 x 1017 atoms of oxygen (2 SF)
Given 1.76 x 1012 molecules of O2, how many moles of iron III oxide
(Fe2O3) can be assembled?
12
1.76 10 molecules O 2 atoms/molecule
2
23
6.02 10 3 atoms/molecule
12
1.95 10 moles Fe O 
2 3



 

10. Chemical Formulae

11. What are chemical formulae?
● short-hand notation
● tells us the types of elements in a compound
● gives the number of atoms of each type of
element in one molecule of the compound
H2SO4 sulphuric acid
4 atoms of oxygen
1 atom of sulfur
2 atoms of hydrogen
1 molecule of H2SO4

12. How many atoms?
C6H12O6 glucose
Mg(NO3)2 magnesium nitrate
Cu(SO4)2●5 H2Ocopper II sulfate
hydrate

13. Relative Formula/Molecular Mass (MR)
The average relative atomic mass (AR) for each element is
noted on the Periodic Table. For example AR for copper
is 63.55. Relative masses are based on 1/12th the mass of
a 12C atom.
The relative formula mass is the total mass of the atoms in
one molecule of a particular compound. For example H2SO4:
Hydrogen 2 atoms × 1.01 = 2.02
Sulfur 1 atom × 32.07 = 32.07
Oxygen 4 atoms × 16.00 = 64.00
MR 98.09

14. Molar Mass

15. Mass and the Mole: Why 6.02×1023?
Consider
1 atom of sulfur AR = 32.07 = 5.326×10-23 grams
Consider
1 mole of sulfur = 6.02×1023 atoms = 32.07 grams
1 mole = 6.02×1023 was chosen because this was then
number of carbon-12 atoms that has a mass of 12
grams.

16. Aluminum AR = 26.98
gram atomic mass = 26.98 g mol-1
Carbon dioxide (CO2) MR = 44.00
gram molecular mass = 44.00 g mol-1
Sodium chloride (NaCl)
Language issue
gram atomic mass
gram molecular mass
gram formula mass
MR = 58.44
gram formula mass = 58.44 g mol-1
MOLAR
MASS

17. We weigh chemical quantities in grams. The molar
mass value for a substance allows us to determine the
number of moles from a measured mass.
Consider 5.68 g of MgCl2
Molar mass of MgCl2 = 95.21 g mol-1
-1
5.68 g
=0.0597 mol
92.51 g mol
0.0597 moles of MgCl2 molecules or….
0.0597 moles of Mg atoms or….
0.119 moles of Cl atoms

18. Atoms combine to form compounds in chemical
reactions.
These combinations occur in whole number
ratios (chemical formulae) – it is the number of
each type of atom that is important (we count
numbers with MOLES)
We measure chemical quantities by MASS.
Molar mass is a very important aspect of
quantitative chemistry because it relates MASS
to MOLES (number of atoms)

19. ÷ 6.02 x 10 Number of 23
atoms,
molecules or
fundamental
units
MOLES
× 6.02 x 1023
MASS
× molar mass
÷ molar mass
molar
mass

20. How many mole are in 45.0 g of water? 2.50 mol
What is the mass of 1.75 mol of CO2? 77.0 g
How many moles of oxygen atoms are in
300 g of CaCO3?
9 moles
What is the mass of 9.03 x 1023 atoms of copper? 95.3 g
106 g of glucose (C6H12O6) is how many moles? 0.589 mol
What is the mass of the oxygen atoms in the previous
question?
56.5 g