OB: moles class #3
Moles with gases,
moles → mass problems
and
moles → particles problems.
Reference tables and calculators
now. Lots of paper please.
Get ready to draw a shark
The mole in chemistry has many connections.
One mole = 6.02 x 1023 particles (atoms, molecules, FU’s, etc.)
One mole = the molar mass of an element
One mole = the molar mass of a compound
Now…
One mole of any gas = 22.4 liters of gas*
*the gas must be at what’s called standard temperature +
pressure which is on table A.
AKA: STP
That’s 273 Kelvin or 0°C
and one atmosphere pressure (normal)
Moles connect mass to volume to numbers of particles. It’s like a
universal math tool that you can use to make amazing connections.
On the next page you will draw a cool map, please use at least one half a
page and be neat. Copy everything especially the shark…
Chemistry
Vacationland
Mole
Island
Volume
Island
1 mole = 22.4 L of gas
Mole
Island
Particle
Island
Mass
Island
Stay on the islands or use the bridges only.
Pay the toll in both directions.
If you try to take a shortcut, the Mole Shark will eat you.
The biggest mole problem is only 2 steps.
Always use units.
Problem #1 today
How many liters of
helium gas are in 65.3 g
of helium?
(hint: start at the beginning)
Figure out where you
are starting, and
where you want to go,
stay on the bridges!
Volume
Island
No Shark Problems.
1 mole = 22.4 L of gas
STEP TWO
Mole
Island
Mass
Island
Particle
Island
65.3 g He
STEP ONE
How many liters of helium gas are in 65.3 grams of helium?
65.3 g He
1
How many liters of helium gas are in 65.3 grams of helium?
Using the map, start at mass island, go to mole island, then go on to volume island.
65.3 g He x 1 mole He
1
4 g He
= 16.3 moles He
16.3 moles He
22.4 L He
x
1
1 mole He
= 365 liters He
This is a 2 step problem, watch SF, go slow, use your units always.
Problem #2, if you find exactly
3.58 x 1024 atoms of aluminum,
how many grams do you have?
This is another 2 step problem, starting at particle
island, to moles, then a trip to mass island.
Problem #2, if you find exactly
3.58 x 1024 atoms of aluminum,
how many grams do you have?
3.58 x 1024 atoms Al x
1
1 mole Al
6.02 x 1023 atoms Al
=
3.58 x 1024 = 0.595 x 101 moles Al
6.02
1023
5.95 moles Al
one more step!
5.95 moles Al
1
x
27 g Al
1 mole Al
= 161 g Al
(3 SF)
The mole island map will be your handy guide through all
mole problems. No problems exist that can’t be figured out
with the map. Always use units, always write big enough to
cancel out, always go slowly, and you cannot go wrong.
Last problem for now: you are re-gifted a
present from your weird Uncle Al. He gives
you a canister that says it contains exactly
7.99 x 1022 molecules of nitrogen gas. What
does this gas weigh? (remember HONClBrIF twins!)
7.99 x 1022 molecules N2
1
X
7.99 x 1022 molecules N2
1
7.99
6.02
x
1022
1023
x
1 mole N2
6.02 x 1023 molecules N2
= 1.33 x 10-1 moles N2
1.33 x 10-1 moles N2 = 0.133 moles N2
0.133 moles N2 x 28 g N2
1 mole N2
1
= 3.72 g N2 gas
=
Next, we’ll do the Mole Lab.
Come on time, come with a calculator
and a smile.
Homework tonight… start reading the
Mole BASICS.
Peace, love and chemistry.