1. Review of Topics Learned:
1. Calculate the molar mass of:
A. magnesium sulfate
B. silver (I) bromide
2. What is the percent composition of oxygen in calcium hydroxide?
3. What is the empirical formula for a compound which contains g of iron, g of sulfur and g of oxygen?
4. Given the following data, find the correct molecular formula 24.3 % C, 4.1 % H, 71.6 % Cl, molecular formula mass = g.

2. 1/30: Pre-AP
Find your mole poster and start working on it. You will have 15 minutes to complete the poster
When finished, stack it on the side table and pick up the molar mass worksheet.
You will need a calculator, something to write with, and a periodic table (You have been given multiple ones over the year, use one of these)
HW: Molar mass worksheet.

3. Counting Atoms

4. Relating Mass to Number of Atoms
How can the mass of an element from the periodic table be related to the actual number of atoms that are present in a sample?
Use:
The mole
Avogadro’s number
Molar mass

5. The Mole
Definition-the amount of substance that contains as many particles as there are atoms in exactly 12 g of carbon-12.
Huh?
If you weighed exactly 12 g of carbon-12 and counted every single atom in your pile, the number of atoms present is defined as 1 mol.
Think of it like exactly 12 eggs are in 1 dozen.

6. Avogadro’s Number So how many carbon-12 atoms would be in that pile?
X 1023
Rounded to X 1023
This number is “nicknamed” Avogadro’s number after the Italian scientist Amedeo Avogadro.
A mole of any substance contains X1023 particles, just like 1 dozen of any substance contains 12 particles.

7. If every person on earth (5 billion) counted continuously at 1 atom per second, it would take 4 million years for all atoms in one mole to be counted!

8. The mass of 1 mole of a pure substance is called the molar mass
Equality that relates number of grams in a mole
Molar mass is equal to the atomic mass of an element
The unit for atomic mass is grams per mole (g/mol)

9. CONCEPTUAL WARM-UP (write your answer on a piece of scratch paper): The pictures below show a mole of water and a mole of gold. 1. Determine the mass (g) of each. Also determine the number of atoms in the gold and the number of molecules in water.

10. Now try this one… 1. How many grams AND how many atoms are in the mole of silver (left pic)? 2. How many grams and atoms are in the mole of carbon (right pic)?

11. Atoms, Moles, & Molar Mass can be used as conversion factors!
When performing conversion between atoms, moles, and grams (molar mass), remember: A M G

12. When using masses from the periodic table, round to two decimals for all calculations!

13. Conversion Example 1 : M-G
What is the mass, in grams, of 2.67 mol of the element copper, Cu?
Given: 2.67 mol Cu
Unknown: ? g Cu

14. Conversion Example 2: A-M
How many moles of oxygen, O, are in 2,000,000 atoms of oxygen?
Given: 2,000,000 atoms O
Unknown: ? mol O

15. Conversion Example 3 A-M
Convert 5.00 X molecules of chlorine gas to moles

16. Conversion Example 4 G-A
How many atoms are in 5.8 gram of copper?

17. Conversion Example 5 A-G
Determine the mass in grams of X 1020 molecules of CO2

18. The remainder of the period:
You will be timed for 8 minutes at each station.
You have this time to answer the question as a group. Write your OWN answers down on a piece of paper.
When time is up: switch to the number FOLLOWING the one you started on .
HW for tonight: the review for the test and the AMG practice problems you picked up from side table.

19. Molar Mass Used to Determine Percent Composition
Molar mass-the mass of one mole of a compound 19

20. Why % composition?
When a new compound is made or discovered, it is analyzed to determine its % composition.
From this info, its empirical formula can be determined. 20

21. Percentage Composition
Percentage by mass of each element in a compound
Percentages should always total very close to 100! Always check! 21

22. Percentage Composition Example 1
Find the percentage composition of sodium nitrate.
Formula of sodium nitrate: NaNO3
Molar mass of NaNO3=85.00 g/mol
Total 100% 22

23. Percentage Composition Example 2
Find the percentage composition of silver sulfate.
Formula of silver sulfate: Ag2SO4
Molar mass of Ag2SO4= g/mol
Total % 23

24. Empirical Formula Simplified formula for a compound
For an ionic compound, empirical formula is the compound’s formula unit because we always simplify the formula
Calcium sulfide: Ca2S2CaS
For a molecular compound, may not represent actual number of atoms present in a molecule
Molecular formula: B2H6
Empirical formula: BH3 24

25. C2H6 CH3 Empirical Formula
Smallest whole number ratio of atoms in a compound
C2H6
reduce subscripts
CH3 25

26. How do you calculate empirical formula?
1. Write down the mass or % of each element given in the problem
2. Divide that number by the mass on the periodic table
3. Divide each number by the smallest number determined in step 2
4. IF you have a number in step 3 that isn’t a whole number (ex. 2.5), then multiply subscripts by 2, 3, or 4 to get whole #’s. 26

27. Empirical Formula Example 1
A compound consist of 75% carbon and 25% hydrogen by mass. Determine the empirical formula for this compound
75 g
1 mol
12.01 g
= 6.24 mol N
= 1 C
6.24 mol
25 g
1 mol
1.01 g
= mol O
= 4 H 27

28. Empirical Formula Example 2
Find the empirical formula for a sample of 25.9% N and 74.1% O.
25.9 g
1 mol
14.01 g
= 1.85 mol N
= 1 N
1.85 mol
74.1 g
1 mol
16.00 g
= 4.63 mol O
= 2.5 O 28

29. Empirical Formula Example
N1O2.5
Need to make the subscripts whole numbers
 multiply by 2
N2O5 29

30. Pre-AP 2/5 Pick up the paper from the side table
Today we will review all topics learned so far in this unit (empirical formula, molar mass, percent composition)
WE will learn how to calculate molecular formula from an empirical formula AND THEN POSSIBLY TAKE A QUIZ (if time permits)
HW: empirical flight project is due Monday.

31. CH3 C2H6 Molecular Formula
“True Formula” - the actual number of atoms in a compound
CH3
empirical
formula ?
C2H6
molecular
formula 31

32. How do you calculate molecular formula?
1. Find the empirical formula.
2. Find the empirical formula mass.
3. Divide the molecular mass by the empirical mass.
4. Multiply each subscript by the answer from step 3. 32

33. Molecular Formula Example
The empirical formula for ethylene is CH2. Find the molecular formula if the molecular mass is 28.1 g/mol.
empirical mass (CH2) = g/mol
28.1 g/mol
14.03 g/mol
= 2.00
(CH2)2  C2H4 33

34. Review of Topics Learned:
1. Calculate the molar mass of:
A. magnesium sulfate
B. silver (I) bromide
2. What is the percent composition of oxygen in calcium hydroxide?
3. What is the empirical formula for a compound which contains g of iron, g of sulfur and g of oxygen?
4. Given the following data, find the correct molecular formula 24.3 % C, 4.1 % H, 71.6 % Cl, molecular formula mass = g.

35. General pathway to solve problems
Mass of each element
Percent composition of compound
Empirical formula for compound
Molecular formula for compound 35

36. Molecular Formula Example
A sample of a compound with a molar mass of g/mol is found to consist of 0.44 g H and 6.92 g O. Find its molecular formula.
5.98 % H, % O
Empirical formula: HO
Molecular formula: (HO)2=H2O2 36