Homework AnswersPage 104, Questions 1-3

1. 24µ2. 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

3. Divide each actual mass by 13.9g:Stir rod: 1.00100 mL beaker: 3.61250 mL flask: 5.38Dish: 1.68Graduate: 4.72

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)

• The mole is the chemist’s 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?

= 3.82 x 1013 centuries= 38.2 trillion centuries!!

(6.02 x 1023) (10s) (1min) (1h) (1d) (1y) (1century) (50 ) (60 s)(60min)(24h)(365d) (100 y)

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

1.008g x 2H16.00gO

Total: 18.02g Molar Mass

1 mol of H2O = 18.0 g= 6.02 x 1023 molecules of H2O

Fe 55.8gFe

1 mol of Fe = 55.8 g= 6.02 x 1023 atoms of Fe

Example: What is the molar mass of:

H2OH2O

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 2wheels1dozen 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

Let’s take it one step further

Example: How many atoms of F are in 4.00 mol of F2?

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 Au1 mol Au

= 3.01x 1017 atoms Au

? atoms F = 4.00 mol F2 x 6.02 x 1023 molecules F2 x 2 atoms F1 mol F2 1 molecule F2

=4.82 x 1024 atoms F

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