Homework Answers Page 104, Questions 13

1
Homework AnswersPage 104, Questions 1-3

• 24µ
• 20.00g 3.33 6.00g? argon is 3.33 times
  heavier than carbon. If carbon is 12µ then argon
  is 3.33 x 12µ 40.0µ
• Divide each actual mass by 13.9gStir
  rod 1.00100 mL beaker 3.61250 mL
  flask 5.38Dish 1.68Graduate 4.72

2
The Meaning of the Chemical Equation
e.g.
2 C(s) O2(g) ? 2 CO(g)

• two atoms of carbon must react with one molecule
  of oxygen to produce two molecules of carbon
  monoxide.
• We can use any multiple of these proportions.

e.g.
4 C(s) 2 O2(g) ? 4 CO(g)
200 C(s) 100 O2(g) ? 200 CO(g)
2 doz C(s) 1 doz O2(g) ? 2 doz CO(g)
The chemist uses moles.
2 moles C(s) 1 mole O2(g) ? 2 moles CO(g)
3
The Mole

• The mole is the chemists dozen
• One mole of anything is 6.02 x 1023 of that thing

e.g.
One mole of cookies is 6.02 x 1023 cookies
5 moles of atoms is 5(6.02 x 1023) 3.01 x 1024
atoms
How long would it take to count to 1 mole?
(6.02 x 1023) (10s) (1min) (1h) (1d) (1y)
(1century) (50 ) (60
s)(60min)(24h)(365d) (100 y)
3.82 x 1013 centuries 38.2 trillion
centuries!!
4
Molar Mass
Molar mass of a compound / element / molecule is
the mass in grams of 1 mole of the particles that
make up the substance.
The molar mass is equivalent to the formula mass
(amu) with units changed to grams
H2O
1 mol of H2O 18.0 g
6.02 x 1023 molecules of H2O
Fe
1 mol of Fe 55.8 g
6.02 x 1023 atoms of Fe
5
Conversion
Involving Moles, Atoms Molecules and Mass
Example How many wheels are there in 12 dozen
bikes? (unitary rates)
? Wheels 12 dozen bikes x 12 bikes x
2wheels 1dozen bikes 1 bike
288 wheels
Example How many Fluorine molecules (F2) are
there in 4.00 mol of fluorine gas
? Molecule F2 4.00 mol F2 x 6.02 x 1023
molecules F2 1 mol F2
2.41 x 1024 molecules F2
6
Lets take it one step further
Example How many atoms of F are in 4.00 mol of
F2?
? atoms F 4.00 mol F2 x 6.02 x 1023 molecules
F2 x 2 atoms F 1 mol F2 1 molecule F2
4.82 x 1024 atoms F
Example How many atoms are equal to 5.00 x 10-7
mol of Au?
? Atoms of Au 5.00x 10-7 mol Au x 6.02 x 1023
atoms Au 1 mol Au
3.01x 1017 atoms Au
Example What is the mass (in grams) of 1 atom of
fluorine?
?g for 1 atom F 1 atom F x 1 mol F
x 19.0 g 6.02 x 1023 atoms 1 mol F
3.16x 10-23 g