Amount of substance
L.O.:
Avogadro constant and the mole.
 Calculate the number of moles in a
given sample.
 Calculate the number of atoms
and/or molecules in a given sample.
Homework: worksheet 2.1
You are chemist. Your job is to produce
substance C.
A + B -> C
(A Mr=20, B Mr =40)
You need 1B per each 1A. How can you count
the molecules?
If I use 20 g of A, how
many grams of B do I
need?
Ar of Hydrogen?
There is 6.022 x 1023 atoms of hydrogen in 1g of
hydrogen atoms.
What is the weight of 6.022 x 1023 atoms of
carbon-12?
Avogadro number= number of atoms in 12 g of
carbon-12.
The mole
Mole = The amount of substance that contains
6.00 x 1023 particles.
1 mole of hydrogen weights 1 g.
1 mole of helium atoms weights________.
1 mole of H2O molecules weights________
The relative molecular mass of a substance in
grams contains one mole of molecules
1 mole of water = 18g
2 moles of water = 32 g
How many moles are there in 64.2 g of sulfur?
(Ar S =32.1)
Molar mass, Mr is the mass per mole of a
substance. The units of molar mass are g mol-1
You can find the molar mass by adding together
al the relative atomic masses for each atom
that makes up a formula unit.
M (CO2)
Determine the molar mass of the following
compounds.
26) KF
27) NaOH
28) Ca3N2
29) MgSO4
30) CH3CO2CH2NH2
31) Ca(OH)2
32) Al2(SO4)3
33) K(NH4)2PO4
Relative Mass
How can we relate the three properties we have just learned about:
mass, m;
molar mass, M; and
amount of substance, n?
m
n
M
m
OR
n
M
What do these equations actually mean?
For example: what is the mass of
1 mole of iron?
Ar = 56 g = mass of 1 mole
What is the mass of 1 mole of
water?
Mr = 18g = mass of 1 mole
Determine the mass of each of the
following:
1) 35.1 mol of K
2) 1.04 mol of Cu
3) .0250 mol of Au
4) 1.90 X 10-2 Mol Of U
How many moles are there in 36 g
of water?
36g/18g in a mole = 2 moles
Determine the number of moles in each of
the following:
1) 23.5 grams of Co
2) 216 grams of Ag
3) .0759 g of W
4) 467.1 kg of K
In one mole of anything, there are
ALWAYS 6.023 x 1023 particles
How many atoms are there in 56 g of iron?
56g/56 g in a mole = 1 mole
6.023 x 1023 atoms in 1 mole = 6.023 x 1023
atoms in 56 g
In one mole of anything, there are
ALWAYS 6.023 x 1023 particles
• How many molecules are there in 36 g of
water?
36g/18g in one mole = 2 moles
6.023 x 1023molecules in one mole x 2 moles
= 12.046 x 1023 molecules in 36 g of water.
Amount of substance
L.O.:
Avogadro constant and the mole.
 Calculate the number of moles in a
given sample.
 Calculate the number of atoms
and/or molecules in a given sample.