1. What does the little number below each
Element mean?
What are its’ units?
amu/atom

2. one amu is defined as 1/12th
What is an amu
one amu is defined as 1/12th of
12C

3. Average atomic mass or atomic weight is determined by a mass spectroscope.
example: Analysis of a sample of carbon was found to have the following isotopes
12C – %
13C – %
14C – %
What is the atomic weight of Carbon

4. 12C – (11.999) (.973) =
13C – (12.998) (.026) =
14C – (13.966) (.0010) =

5. How high could you stack a mole of sheets of paper?
How much is a mole?
How high could you stack a mole of sheets of paper?

6. How much would a mole of iron weigh? Could you lift it?
Look on the back inside cover for amu and mole
x 1023 atoms of Fe
55.85 amu
x g*
=55.85 g
1atom of Fe
1 amu

7. What is the Mole?
One mole is equal to the number of carbon atoms in exactly grams of C-12: 6.02 x 1023 atoms

8. The Shopping Mole x g/ mole 22.4 L / mole
# of atoms or molecules
6.02 x atoms or molecules/mole
Mole
x g/ mole
22.4 L / mole
Mass of atom
or molecule
volume of gas
The Shopping Mole

9. Calculate the numbers of atoms of cesium found in 3.57 moles of cesium
Calculate the numbers of atoms of cesium found in 3.57grams of cesium
Calculate the mass of 4.82 x 1023 atoms of cesium

10. 1. Calculate the mass of 4.65 moles of (NH4)2S
Calculating the molar mass of a compound (NH4)2S
1. Calculate the mass of 4.65 moles of (NH4)2S
2. Calculate the numbers of atoms of nitrogen found in 3.57grams (NH4)2S
3. Calculate the mass of nitrogen in 3.76 x 1024 formula units of (NH4)2S

11. Determining Percent Composition of Compounds
Given the compound: Al(HPO3)3
What are the percent compositions of each of the atoms from which the above compound is constructed?
Mass of Aluminum= 1 mol Al
26.9 grams
= 26.9g Al
mole of Al
Mass of hydrogen = 3 mols H
1.01 gram
= H
mole of H
266 g
Al(HPO3)3
Mass of Phosphorus = 3 mols P
30.9 gram
= g P
mole of P
Mass of oxygen = 9 mols O
16.0 gram
= 144 g O
mole of P

12. 10.1% Mass percent of Al: 1.13% Mass percent of H: 34.8%
mass of Al
26.9 g
10.1% =
x 100 =
Mass percent of Al:
mass of Al(HPO3)3
266 g
mass of H
3.03 g
x 100
1.13% =
Mass percent of H: =
mass of Al(HPO3)3
266 g
mass of P
92.7 g
34.8%
x 100
Mass percent of P: = =
mass of Al(HPO3)3
266 g
mass of O
54.1%
144 g = =
x 100
Mass percent of O:
266 g
mass of Al(HPO3)3

13. Empirical formula
A compound is composed of Cl 71.65% and C 24.27% and H 4.07% what is the empirical formula? The Molar mass is 98.96g/mole, what is the molecular formula?

14. 0.255 g isopropyl alcohol is combusted
Determining the Empirical Formula of a Compound Using Combustion Analysis
Combustion Analysis
0.255 g isopropyl alcohol is combusted
mass difference of H2O absorber = g
mass difference of CO2 absorber = g

15. mass difference of H2O absorber = 0.306 g
mass difference of CO2 absorber = g
1 mole CO2
12 g C
grams of C: g CO2
= 0.153g C
44 g CO2
1 mole CO2
1 mole H2O
2.02 g H
grams of H: g H2O
= g H
18 g H2O
1 mole H2O
grams of O: g g g H = g

16. Assume that the empirical formula for the compound is C3H8O
1 mol C 1
C: g C
= 2.97
= mol C
12 g C
0.0043
1 mol H 1
H: g H
= 7.91
= mol C
0.0043
1.01 g H 1
1 mol O
O: g O
= 1.00
= mol O
0.0043
16 g O
Assume that the empirical formula for the compound is C3H8O

17. Ascorbic acid (Vitamin C) contains 40. 92 percent C, 4
Ascorbic acid (Vitamin C) contains percent C, 4.58 percent H, and percent O by mass. What is the empirical formula of ascorbic acid?
Ethylene glycol, the substance used in automobile antifreeze, is composed of 48.7 % C, 9.7 percent H, and 51.6 percent O by mass. Its molar mass is
62.1 g/mol. (a) What is the empirical formula of ethylene glycol? (b) What is the molecular formula

18. So What is Stoichiometry?
mass of A in g mole 3(moles C) C g = mass C
A g 1(moles A) mole
1A + 2B → 3C + 4D

19. Na2SO3(aq) + 2AgNO3(aq)  Ag2SO3(s) + 2NaNO3(aq)
If 3.4 g of silver nitrate is mixed w/ excess sodium sulfite, what would be the theoretical yield for silver sulfite?
in moles
in formula units
in L at STP
in grams

20. Na2SO3(aq) + 2AgNO3(aq)  Ag2SO3(s) + 2NaNO3(aq)
If 3.4 g of silver nitrate is mixed sodium sulfite, how many grams of sodium sulfite would you need to react completely?

21. Na2SO3(aq) + 2AgNO3(aq)  Ag2SO3(s) + 2NaNO3(aq)
If 4.5 g of sodium sulfite is mixed w/ excess silver nitrate, what would be the theoretical yield for silver sulfite?
What would be the percent yield if 4.1g was produced in the lab?

22. Na2SO3(aq) + 2AgNO3(aq)  Ag2SO3(s) + 2NaNO3(aq)
If 4.3 g of silver nitrate is mixed w/ 3.2g sodium sulfite, what would be the theoretical yield for silver sulfite?
How much of the excess reagent is left over?

23. Using Stoichiometry in the Laboratory
Na2SO3(aq) + 2AgNO3(aq)  Ag2SO3(s) + 2NaNO3(aq)
20 ml
0.12 M
20 ml
0.35 M
1. How many grams of silver sulfite would be produced?
2. What would be the molarity of the sodium nitrate?