1. Chapter 1: Stoichiometric relationships

2. 1.2: The mole concept Note: You should review naming
Use the chemistry help page on website for some review videos
Click image!

3. Avogadro’s number and relative atomic mass
Avogadro’s # (L or NA) = 6.02x1023 = 1 mol
Relative Atomic mass (Ar)
The weighted average of the different isotopes that exist in nature
Has NO units!
Ar= weighted average of 1 atom of element
1/12 mass of one atom of Carbon-12
Isotope Carbon-12 is the international reference point for measuring atomic (and therefore molecular and molar) masses
Carbon-12 has a value of exactly 12
1/12 of an atom of Carbon-12 has a value of exactly 1

4. Mole conversion examples
How many formula units are in 0.5 moles of NaCl?
How many grams are in 5.0 moles of hydrogen perioxide?
How many moles are in 0.3 g of Iron(IV)Oxide?
How many atoms are in 2.4 moles of water?

5. Relative molecular/formula mass and molar mass
Relative Molecular/formula mass (Mr)
The sum of the weighted average atomic masses in a compound
Has NO units!
Mr of H2O = H + H + O where H = 1.01 and O = 15.99
Mr of H2O = = 18.01
Molar mass (M)
The mass of 1 mole of a substance
Units are g mol-1
n = number of moles (mol)
m = mass in grams (g)
M= molar mass (g mol-1)

6. Mole conversion examples
How many moles are in 52 grams of ice?
How many grams are in 3 moles of dry ice?
What is the molar mass of a sample that is has 5 grams and 0.25 moles?
If the previous sample was made of only one atom, what might the identity of that element be?

7. Mole ratios – compounds
1 mole of a substance is 6.02x1023
So if we have 1 mol of Na2SO4, then we have:
1 mol of S atoms
2 mol of Na atoms
4 mol of O atoms
If we have 2 mol of H2O, then we have:
4 mol of H atoms
2 mol of O atoms
If we have 0.5 mol of FeO2, then we have:
0.5 mol of Fe atoms
1 mol of O atoms

8. Mole ratios – equations
Use the following equation:
2H2 + O2  2H2O
If we have 1 mol of O2:
We need 2 mol of H2 to make 2 mol of H2O
If we have 2 mol of O2:
We need 4 mol of H2 to make 4 mol of H2O
If we have 1 mol H2:
We need 0.5 mol of O2 to make 1 mol of H2O
If we need to make 5 mol H2O:
We need 5 mol H2 and 2.5 mol O2

9. Empirical formulas The simplest ratio of atoms in a compound
MgO CH4 C2H6O7
Empirical means “experimental”
What is the empirical formula for:
C2H6
Ag2N6O2
N3O9
Si4O10

10. Empirical formulas
How to calculate Empirical Formulas from experimental data:
A sample contains 63.5 g Ag, 8.2 g N and g O. What is the empirical formula of the compound?

11. Empirical formulas – easy
Tetraethyl lead, a gasoline additive, is found to contain g lead, g carbon, and g hydrogen. What is its empirical formula?

12. Empirical formulas – medium
An oxide of chromium is found to have the following % composition: 68.4% Cr and 31.6% O. What is the empirical formula?

13. Empirical formulas – Hard
g of an organic compound is known to contain g of carbon, g of hydrogen, g of oxygen and the rest is nitrogen. What is the empirical formula of the compound?

14. Molecular formulas from empirical formulas – easy
An empirical formula is determined to be NO2 and the molar mass is 92.5 g mol-1. What is the Molecular Formula?

15. Molecular formulas from empirical formulas – medium
A sample with molecular mass of 170 g mol-1 contains 63.5 g Ag, 8.2 g N and 28.3 g O. What is the molecular formula of the compound?

16. Molecular formulas – hard
A 10g sample of a compound contains 4.00g C, 0.667g H, and the rest is Oxygen. Find the empirical and molecular formulas. The MW is 180.

17. Empirical formulas: hydrates
What happens when something hydrated is dehydrated?
Hydrate: compound that has water bound
Ex: copper sulfate pentahydrate (CuSO4∙5H2O) and copper sulfate trihydrate (CuSO4∙3H2O)
Ex: Na2CO3∙10H2O MgSO4∙7H2O
Anhydrous: water has been removed from hydrate
Ex: anhydrous copper sulfate (CuSO4)
Ex: Na2CO3 MgSO4

18. Empirical formulas: hydrates - easy
barium chloride dihydrate = ___________
What is the percent composition of water in the compound above?
36.04 / x 100 = 14.6%
Magnesium sulfate heptahydrate = _____________
If 125 grams of the compound above is completely dehydrated, how many grams of anhydrous magnesium sulfate will remain?
100 – = % magnesium sulfate
x 125 = 61.1 grams

19. Empirical formulas: hydrates – medium
A 20g sample of a hydrate of nickel sulfate (NiSO4) lost 9.63g of water when heated. Determine the hydrate’s formula.

20. Empirical formulas: hydrates - hard
A hydrate containing copper, sulfur, oxygen, and water lost 9g upon heating. Originally the hydrate had weighed 25g. Analysis of the anhydrous substance revealed that the 6.4g of Cu, 3.2g of S, and 6.4g of O were present. Find the formula of the hydrate.
Ermahgerd!!!!.....whaaaat???

21. A hydrate containing copper, sulfur, oxygen, and water lost 9g upon heating. Originally the hydrate had weighed 25g. Analysis of the anhydrous substance revealed that the 6.4g of Cu, 3.2g of S, and 6.4g of O were present. Find the formula of the hydrate.

22. A hydrate containing copper, sulfur, oxygen, and water lost 9g upon heating. Originally the hydrate had weighed 25g. Analysis of the anhydrous substance revealed that the 6.4g of Cu, 3.2g of S, and 6.4g of O were present. Find the formula of the hydrate.

23. Empirical formulas: Percentage composition
Percentage composition by mass can be calculated from the empirical formula!
What percentage by mass of hydrogen (H) is in water?
What is the percentage by mass of N and O in NO3?
What is the percentage by mass of H, S and O in H2SO4?

24. Empirical formulas: Combustion analysis
What are the products of the combustion of a hydrocarbon?
CH4 + O2  CO2 + H2O
For the amount of carbon in the original hydrocarbon, this is equal to the number of CO2 molecules formed.
For the amount of hydrogen in the original hydrocarbon, the water reflects this value.

25. A gram sample of an organic compound was combusted in oxygen producing grams of CO2 and grams of H2O. In addition it was found that the compound contained 27.59% oxygen. What is the empirical formula of the compound?

26. A 12 g sample of a smelly compound was tested by combustion analysis
A 12 g sample of a smelly compound was tested by combustion analysis. The products were g of CO2, g of H2O, and grams of N2O5. Further analysis showed that oxygen was NOT present in the molecule. What is the empirical formula of the compound?

27. Empirical formulas: Combustion analysis
A g sample of a hydrocarbon that contains oxygen, caproic acid, is combusted producing 0.512g CO2 and g H2O. The molar mass of the acid is 116g mol-1 what is the molecular formula for caproic acid?