Transcript Slide 1

Moles
Mole:
A)
B)
C)
D)
A small blind burrowing furry rodent
A spy
A skin condition
6.02 x 10 23
Mole:
A)
B)
C)
D)
A small blind burrowing furry rodent
A spy
A skin condition
6.02 x 10 23
6.02 x 10 23
is called Avogadro’s Number
and a Mole
This is COLLECTIVE NOUN
What is the collective noun name for 12?
A dozen
Working with collective nouns
• A Dozen is easy to work with because the
number 12 is a small number.
•
•
•
•
Two dozen
= 2 x 12 = 24
A half dozen
= 12/2 = 6
163.67 dozen
= ????
163.67 x 12
= 1964.04
(lots of eggs, or donuts or whatever…!)
Working with collective nouns
• A Mole is easy to work with because the
number 6.02 x 10 23 is a
number.
•
•
•
•
Two moles = 2 x (6.02 x 10 23 )= 12.04 x 1023
A half mole = (6.02 x 10 23 )/2 = 3.01 x 1023
163.67 moles = ????
163.67 x (6.02 x 10 23 ) = 985.3 x 1023
(lots and lots of eggs, or donuts or
whatever…!)
Review: Working with exponents
2 x (6.02 x 10 23 )= 12.04 x 1023
= 1.204 x 1024
163.67 x (6.02 x 10 23 ) = 985.3 x 1023
= 9.853 x 1025
Where did the Mole come from?
A Mole is defined as the number of atoms of
Carbon in 12.000 grams of carbon.
(did somebody really count these out?)
Why 12 grams of Carbon?
Remember: The amu is based on Carbon-12
One carbon atom has a mass of 12 amu
But who can work with one carbon atom???
Why 12 grams of Carbon?
It just so happens that…
One carbon atom has a mass of 12 amu
One MOLE of carbons atoms has a mass of
12 grams
Grams are easy to work with !
But this magic doesn’t just work for
Carbon!
The atomic mass (in grams) of any atom is
the mass of one MOLE of that element
The gram formula mass of any compound is
the mass of one MOLE of that compound
Since chemists are unbelievably
lazy….
MOLE
is often abbreviated as
MOL
Moles and GFM
Since the gram formula mass is the mass of one
mole, we can write this mathematically as:
GFM =
grams per mole
= grams/mole
= grams
mole
Moles and GFM
So,
for Na, with a GFM of 23 g
There are 23 grams per mole of Na
= 23 grams/mole
= 23 grams
mole
Moles and GFM
So,
for NaCl, with a GFM of 58 g
There are 58 grams per mole of NaCl
= 58 grams/mole
= 58 grams
mole
Converting grams to Moles
This formula is in Table T;
# of moles = given mass
gram formula mass
Converting grams to Moles
# of moles = given mass
gram formula mass
How many moles of Na are in 333 g of Na?
# of moles = 333g
23g/mole
# of moles = 14.48 g/g/mole
= 14.48 moles
You try it!
How many moles are there in 678 grams of
NaCl?
# of moles = 678 grams
GFM
# of moles = 678 grams NaCl
58.5 g/mol
GFM of NaCl = 23 + 35.5
= 58.5g/mol
= 11.6 mole NaCl
Converting Moles to Grams
This formula is NOT in Table T, but you can
get it by rearranging the grams to mole
formula
Grams = # of moles x GFM
Grams = # of moles x grams
mole
Converting Moles to Grams
Grams = # of moles x GFM
How many grams are there in 6.37 moles of
Na?
Grams = 6.37 moles x 23 grams Na
mole
Grams = 147 grams Na
You try it!
Grams = # of moles x GFM
How many grams are there in 106.8 moles
of NaCl?
Grams = 106.8 moles x 58.5 grams/mol
= 6248 grams NaCl
Mole Relationships in chemical
equations
A recipe calls for:
To make double the
amount:
2 cups flour
4 eggs
1/2 cup chocolate chips
4 cups flour
8 eggs
1 cup chocolate chips
Mole Relationships in chemical
equations
A recipe calls for:
To make half the
amount:
2 cups flour
4 eggs
1/2 cup chocolate chips
1 cups flour
2 eggs
1/4 cup chocolate chips
You can write this as a chemical
reaction (all cooking is!)
2 cups flour + 4 eggs + ½ cup chips
2
4
.5
1 cake
1
These numbers show the RATIOS of ingredients in the
recipe that make it come out right
If you know the correct ratios, you can double, triple or
halve the recipe easily.
2 cups flour + 4 eggs + ½ cup chips
2
4
.5
1 cake
1
Suppose you only have 3 eggs ? How much flour will you need?
4 eggs (original recipe)
3 eggs (new recipe)
= 2 cups flour (original recipe)
X cups flour (new recipe)
Cross multiply and solve for x
4X = 2x3
X= 6
4
X = 1.5 cups flour
2 cups flour + 4 eggs + ½ cup chips
2
4
.5
1 cake
1
Suppose you only have 3 eggs ? How many cups of chips
will you need?
4 eggs (original recipe)
3 eggs (new recipe)
= .5 cups chips (original recipe)
X cups chips (new recipe)
Cross multiply and solve for x
4X = .5 x 3
X = 1.5
4
X = .375 cups chips
2 cups flour + 4 eggs + ½ cup chips
2
4
.5
1 cake
1
Suppose you only have 3 eggs ? How many cakes can you make?
4 eggs (original recipe)
3 eggs (new recipe)
= 1 cake (original recipe)
X cakes (new recipe)
Cross multiply and solve for x
4X = 1 x 3
X= 3
4
X = .75 cakes
In balanced chemical equations..
the coefficients in front of the formulas can
be interpreted two ways:
as numbers of molecules (easy to visualize)
Or
As number of moles (practical in the lab)
4 NH3 + 5O2
4NO + 6H2O
How many moles of water will be produced if 3 moles
of ethane are burned?
2 C2H6 + 7 O2
2
7
4 CO2 + 6 H2O
4
6 (original)
3
?
?
2 moles ethane (original)
3 moles ethane (new)
2X = 3 x 6
X = 18/2
=
X (new)
6 moles water (original)
X moles water (new)
X = 9 moles water
You try: How many moles of carbon dioxide will be produced?
How many moles of oxygen gas will be needed?