Transcript 5-1-mole-concept - St John Brebeuf

Unit V: The Mole Concept
Chemical Calculations
Atoms and molecules are extremely small.
If they are so small and so light, how can we weigh them?
We weigh large numbers of them.
Avogadro took 1.00 g of the smallest atom (H) and determined how
many H atoms there are in 1.00 g of H.
He found that:
1.00 g H
= 6.02 x 1023 atoms = 1.00 mole
This is called Avogadro’s number
1 dozen donuts = 12 donuts
1 century
1 millennium
1.00 mole
= 100 years
= 1000 years
= 6.02 x 1023 particles
The mole is a large number of particles
Particle
Atom
element
Cu
6.02 x 1023 at
1 mole
Molecule
covalent
CH4
6.02 x 1023 molecules
1 mole
Formula Unit
ionic
NaCl
6.02 x 1023 FUs
1 mole
1. Convert 2.5 x 1025 at C to moles
2.5 x 1025 at
x
1 mole
6.02 x 1023 at
=
42 moles C
2. Convert 16.3 moles CO2 to molecules
16.3 moles
x
6.02 x 1023 molecules
1mole
= 9.81 x 1024 molecules
3. Convert 8.9 x 1024 molecules CO2 to moles
8.9 x 1024 molecules
x
1 mole
=
6.02 x 1023 molecules
15 moles CO2
4. Convert 28 moles NaCl to Formula Units
28 moles
x
6.02 x 1023 FU
1mole
= 1.7 x 1025 FUs
1.
CO2
m
2.
KCl
fu
3.
C
at
4.
AgNO3
fu
5.
NH4CH3COO
fu
6.
O2
m
7.
Os
at
Determining Avogadro’s Number
Electrolysis Apparatus
Ampmeter
Power Supply
Stop Watch
Determining Avogadro’s Number
Produce a volume of hydrogen gas while measuring the time and
electrical current.
Volume of H2
Time
Current
10.0 mL
80.7 s
0.913 amp
Background information
1 amp is defined as the number of coulombs per second.
There are 6.24 x 1018 electrons in a coulomb.
The density of H2 is 0.07871 g/L.
It takes 1 electron to make 1 H atom
1. Calculate the number of atoms of H, starting with the time.
80.7 s x 0.913 coul x 6.24 x 1018 el
s
1 coul
x 1 at H
1 el
= 4.5976 x 1020 at
2. Calculate the number of grams H starting with the volume of H.
10.0 mL x
1L
1000 mL
x
0.07871 g
1L
= 7.871 x 10-4 g H
3.
Divide the atoms of H by the grams of H to get the number of H
atoms in a gram which is Avogadro’s number.
4.5976 x 1020 at
7.871 x 10-4 g H
=
5.84 x 1023 at/ 1 gram H
=
5.84 x 1023 at/ 1 mole
https://www.youtube.com/watch?v=PvT51M0ek5c
Avogadro’s Hypothesis: Equal volumes of different gases, at the
same temperature and pressure, contain the same number of particles.
V.1 AVOGADRO’S HYPOTHESIS
• Avogadro’s hypothesis: Equal volumes of different gases contain the
same number of particles (at the same temperature and pressure).
• If 1L of gas A reacts with 1L of gas B, then the formula for the
compound is AB
• If 2 L of gas A reacts with 1L of gas B, then the formula for the
compound is A2B
• If 2 L of gas A reacts with 3L of gas B, then the formula for the
compound is A2B3
• Questions: p. 78 #2-5
• Describe each particle as an
atom, molecule or a formula unit. •
• 1.
CO
•
• 2.
KI
•
• 3.
Ne
•
• 4.
FeC2O4
•
• 5.
NaSO4•10H2O
•
• 6.
H2
•
• 7.
Li
8.
SO3
9.
RbCl
10.
CaCO3
11.
Ag
12.
NH3
13.
Cl2
14.
Se