1. The Mole
Q: how long would it take to spend a mole of $1 coins if they were being spent at a rate of 1 billion per second?

2. Background: atomic masses
Look at the “atomic masses” on the periodic table. What do these represent?
E.g. the atomic mass of C is 12 (atomic # is 6)
We know there are 6 protons and 6 neutrons
Protons and neutrons have roughly the same mass. So, C weighs 12 u (atomic mass units).
What is the actual mass of a C atom?
Answer: approx. 2 x grams (protons and neutrons each weigh about 1.7 x10-24 grams)
Two problems
Atomic masses do not convert easily to grams
They can’t be weighed (they are too small)

3. The Mole With these problems, why use atomic mass at all?
Masses give information about # of p+, n0, e–
It is useful to know relative mass
E.g. Q - What ratio is needed to make H2O?
A - 2:1 by atoms, but 2:16 by mass
It is useful to associate atomic mass with a mass in grams. It has been found that
1 g H, 12 g C, or 23 g Na have 6.02 x 1023 atoms
6.02 x 1023 is a “mole” or “Avogadro’s number”
“mol” is used in equations, “mole” is used in writing; one gram = 1 g, one mole = 1 mol.
Read 4.3 (167-9). Stop after text beside fig 2.
Do Q1-6. Challenge: 1st slide (use reasonable units)

4. The Mole: Answers
A mole is a number (like a dozen). Having this number of atoms allows us to easily convert atomic masses to molar masses.
6.02 x 1023
3.00 x 6.02 x 1023 = x 1023 or 1.81 x 1024
(note: there are 3 moles of atoms in one mole of CO2 molecules. In other words, there are 5.42 x 1024 atoms in 3.00 mol CO2)
3.01 x 1023
a) 1.43 kg  12 = kg per orange
b) 1.01 g  6.02 x = 1.68 x 10 –24 g

5. A: It would take 19 million years
Mollionaire
Q: how long would it take to spend a mole of $1 coins if they were being spent at a rate of 1 billion per second?
A: $ 6.02 x 1023 / $
= 6.02 x 1014 payments = 6.02 x 1014 seconds
6.02 x 1014 seconds / 60 = x 1013 minutes
1.003 x 1013 minutes / 60 = x 1011 hours
1.672 x 1011 hours / 24 = x 109 days
6.968 x 109 days / = x 107 years
A: It would take 19 million years

6. Comparing sugar (C12H22O11) & H2O
Same
1 gram each
1 mol each
volume?
No, they have dif. densities.
No, molecules have dif. sizes.
mass?
Yes, that’s what grams are.
No, molecules have dif. masses
# of moles?
No, they have dif. molar masses
Yes.
# of molecules?
No, they have dif. molar masses
Yes (6.02 x 1023 in each)
# of atoms?
No, sugar has more (45:3 ratio) No

7. Molar mass The mass of one mole is called “molar mass”
E.g. 1 mol Li = 6.94 g Li
This is expressed as 6.94 g/mol
What are the following molar masses?
S SO2
Cu3(BO3)2
32.06 g/mol
64.06 g/mol
g/mol
Calculate molar masses (to 2 decimal places)
CaCl2
(NH4)2CO3 O2
Pb3(PO4)2
C6H12O6
Cu x 3 = x 3 =
B x 2 = x 2 =
O x 6 = x 6 =
308.27

8. Molar mass The mass of one mole is called “molar mass”
E.g. 1 mol Li = 6.94 g Li
This is expressed as 6.94 g/mol
What are the following molar masses?
S SO2
Cu3(BO3)2
32.06 g/mol
64.06 g/mol
g/mol
Calculate molar masses (to 2 decimal places)
CaCl2
(NH4)2CO3 O2
Pb3(PO4)2
C6H12O6
g/mol (Ca x 1, Cl x 2)
96.11 g/mol (N x 2, H x 8, C x 1, O x 3)
32.00 g/mol (O x 2)
g/mol (Pb x 3, P x 2, O x 8)
g/mol (C x 6, H x 12, O x 6)

9. Converting between grams and moles
If we are given the # of grams of a compound we can determine the # of moles, & vise-versa
In order to convert from one to the other you must first calculate molar mass
g = mol x g/mol
mol = g  g/mol
This can be represented in an “equation triangle” g
mol
g/mol
g= g/mol x mol
0.25
HCl
53.15
H2SO4
3.55
NaCl
1.27 Cu
Equation
mol (n) g
g/mol
Formula
36.46
9.1
98.08
0.5419
mol= g  g/mol
58.44
207
g= g/mol x mol
63.55
0.0200
mol= g  g/mol

10. Simplest and molecular formulae
Consider NaCl (ionic) vs. H2O2 (covalent) Cl Na Cl H O Na H O H O Cl Cl Na Na
Chemical formulas are either “simplest” (a.k.a. “empirical”) or “molecular”. Ionic compounds are always expressed as simplest formulas.
Covalent compounds can either be molecular formulas (I.e. H2O2) or simplest (e.g. HO)
Q - Write simplest formulas for propene (C3H6),
C2H2, glucose (C6H12O6), octane (C8H14)
Q - Identify these as simplest formula, molecular
formula, or both H2O, C4H10, CH, NaCl

11. For more lessons, visit www.chalkbored.com
Answers
For more lessons, visit
Q - Write simplest formulas for propene (C3H6),
C2H2, glucose (C6H12O6), octane (C8H14)
Q - Identify these as simplest formula, molecular
formula, or both H2O, C4H10, CH, NaCl
A - CH2
A - H2O is both simplest and molecular
C4H10 is molecular (C2H5 would be simplest)
CH is simplest (not molecular since CH can’t form a molecule - recall Lewis diagrams)
NaCl is simplest (it’s ionic, thus it doesn’t form molecules; it has no molecular formula) CH
CH2O
C4H7