UNIT 5 – Stoichiometry & The Mole
Chapter 10 – Chemical Quantities
Chapter 12 – Stoichiometry
Chapter 10
Chemical Quantities
Anything in black letters = write it in
your notes (‘knowts’)
Some similar but slightly different terms…
Atomic Mass - mass of an atom (a.m.u.)
1 C atom = 12.011 a.m.u.
Molecular Mass - mass of a molecule (a.m.u.)
1 CO2 molecule = 12.011 + 2(15.999)
= 44.009 a.m.u.
Formula Mass - mass of a formula unit (a.m.u.)
1 MgO formula unit = 24.305 + 15.999
= 40.304 a.m.u.
10.3 – Percent Composition
Percent Composition of a Compound
mass due to atom(s)
=
x 100
total mass of compound
Example: calculate the percent composition of
oxygen in K2CrO4
Example: calculate the percent composition of
oxygen in K2Cr2O7
ASSIGNMENT:
Chapter 10 Worksheet #1
10.1 – The Mole
A mole is a number of particles
1 mole = 6.02 x 1023 particles
Avogadro’s Number
A particle can be an atom,
molecule, formula unit, ion, etc
Mole is abbreviated as mol – no joke!
Mole – latin for large structure
How big is Avogadro’s Number?
If you could travel at the speed of light,
it would take you more than 100 billion
years to travel 6.02 x 1023 miles.
6.02 x 1023 baseballs would cover the
Earth to a height of several hundred
miles.
How big is Avogadro’s Number?
A computer that can make 200 million
counts per second would need almost
100 million years to count up to 6.02 x 1023
A stack of paper with 6.02 x 1023
sheets would be so tall that it would
reach from here to the sun—not just
once but more than a million times!
How big is Avogadro’s Number?
If 6.02 x 1023 dollars were divided among
the 7 billion people on Earth, we would
have enough money that each of us could
spend a million dollars every minute, night
and day, for as long as we lived an still
have more than half of it left.
…but where would we put all those dollars?
What is the point of a mole?
What is the point of a dozen?
To count large numbers of particles easier.
Yes, the mole was created to make things EASIER!
You will have to be able to measure an amount of
matter and convert to moles of that substance.
The number of moles really tells you the number of
particles (atoms, molecules or formula units).
Atomic Mass – mass of an atom (a.m.u.)
Molecular Mass – mass of a molecule (a.m.u.)
Formula Mass – mass of a formula unit (a.m.u.)
6.02 x 1023
Molar Mass – mass of 1 mole of particles
measured in grams
The molar mass (in grams) equals the
particle’s mass (in a.m.u.)
Examples…
1 atom Na = 22.99 a.m.u.
6.02 x 1023 Na atoms (1 mol) = 22.99 g Na
1 formula unit NaCl = 58.44 a.m.u.
6.02 x 1023 NaCl formula units (1 mol) = 58.44 g NaCl
1 molecule H2O = 18.0 a.m.u.
6.02 x 1023 H2O molecules (1 mol) = 18.0 g H2O
We will rarely talk about 6.02 x 1023
because it is large and inconvenient.
Just say ‘1 mole’ instead of ‘6.02 x 1023’
The molar mass is used as a
conversion factor between grams
and moles.
Remember conversion factors???
Conversion factors are equalities that can
be used to convert from 1 unit to another.
12 inches = 1 foot
60 sec = 1 min
know any others…?
Conversion factors are set up so that
units will cancel.
Example: Convert 20.5 inches into feet.
12 inches = 1 foot
1 foot
_________
20.5 inches x
= 1.708333… feet
12 inches
= 1.71 feet
“Multiply by the top, divide by the bottom.”
Converting from moles to grams
Molar mass of MgO
40.304
g MgO
_________
2.2 mol MgO x
1 mol MgO
= 88.669 g MgO
= 89 g MgO
Converting from grams to moles
Molar mass of MgO
1 mol CaCl2
_____________
10.1 g CaCl2 x
110.986 g CaCl2
= 0.0910 mol CaCl2
ASSIGNMENT:
Chapter 10 Worksheet #2
How to convert from grams to moles
you need to calculate the molar mass, then use it as a
conversion factor
How to convert from moles to grams
you need to calculate the molar mass, then use it as a
conversion factor
If you ever need to know the number of particles…
use 1 mole = 6.02 x 1023
as a conversion factor
EXTRA STUFF BEYOND THIS SLIDE…
Say that an egg has a mass of 10 grams and bowling ball
has mass of 5 kg
Quantity
4 dozen eggs
4 mol eggs
4 dozen bowling balls
4 mol bowling balls
Mass
Apples can be measured in three different ways
•
At a fruit stand, they are often
sold by the count.
•
In a supermarket, you usually
buy apples by weight or mass.
•
At an orchard, you can buy
apples by volume.
By count: 1 dozen apples = 12 apples
By mass: 1 dozen apples = 2.0 kg apples
By volume: 1 dozen apples = 0.20 bushel apples
Example: Use conversion factors to calculate
how many apples are in 1 bushel?
By count: 1 dozen apples = 12 apples
By mass: 1 dozen apples = 2.0 kg apples
By volume: 1 dozen apples = 0.20 bushel apples
“Multiply by the top, divide by the bottom.”
Example: What is the mass of 90 average-sized
apples if 1 dozen apples have a mass of 2.0 kg?
“Multiply by the top, divide by the bottom.”