1. The Mole & Chemical Formulas

2. The Mole
Mole, abbreviated mol, is the SI (metric) base unit to measure the amount of a substance
It is called Avogadro’s number in honor of Italian physicist Amedeo Avogadro, who discovered one mole of gas in 1811
x 1023 representative particles
602,000,000,000,000,000,000,000

3. Use of the Mole One wouldn’t use this unit for everything
A mole of marbles would cover the surface of the Earth down to approximately 6 kilometers
Although a mole of $1.00 bills would be nice!
It is used to measure the amount of molecules in a substance

4. Conversion Recall 5,280 feet = 1 mile
How many miles would you have in 12,369 feet?
It is the same system of proportions except now its…
1 mole = 6.02x1023
So, if you had 2.5 moles of H2O, how many atoms of water do you have?

5. Recall Determine the number of atoms in 2.75 moles of Zn?
If you had 9 moles of Cu(OH), how many molecules are present?
Lets change it up!
How many moles of H2SO4 if you had 2.11x1024 molecules?

6. Mass & The Moles
A dozen oranges won’t have the same mass a dozen watermelons
But you do have exactly the same amount of each 12
Since they have different compositions, their mass will be different as well
Thus, the mass of 1 mole of silver nitrate (AgNO3) will be different than 1 mole of oxygen gas (O2)

7. Periodic Table Recall
The atomic masses on the periodic table are not whole numbers
They are weighted averages of the masses of all naturally occurring isotopes of each element
Knowing this and using this new idea…
Carbon – 12 is the standard atom used to determine the number of representative particles per mole
We can calculate the molar mass or mass in grams of one mole of any pure substance (g/mol)!

8. So What Does This Mean? Periodic Table Transitions** You Try!
Carbon has a mass of 12
Thus 12 g of carbon = 1 mole of Carbon
Manganese (Mn) has an atomic mass of amu
55 g of Mn = 1 mol Mn
You Try!
3 mol Mn = ? g Mn
136 g Pb = ? Mol Pb
Challenge*
How many grams of gold are found in 7.65x1022 Au atoms?
This works for compounds as well as single elements
1.00 g H2O = ? Mol H2O
1.00 g H2O = ? Molecules H2O

9. Percent Composition
Percent Composition: The percentage by mass of each element in a compound
It is determined by gravimetric and volumetric analyses for solids and liquids, respectively
Example:
100 g of an unknown substance has two elements: X & Y
X has 55 g and y has 45 g of the total 100
(55 g of element X / 100 g cmpd.)*100% = 55%
(45 g of element Y / 100 g cmpd.)*100% = 45%

10. Percent Composition
If you know the compound in question, you can calculate the percent composition for the known atoms
Example: g/mol H2O
Hydrogen (H) – g
Oxygen (O) – g
g * 2 Hydrogen in water = 2.02 g
(2.02 g H / g H2O) * 100 = 11.2 % H
16.00 g O * 1 Oxygen in water = g
(16.00 g O / g H2O) * 100 = 88.8 % O
So, water is 11.2% Hydrogen and 88.8% Oxygen
Try 8.00 g of Cu(OH)

11. Empirical Formula
After you have identified the compound and its percent composition, you can find the formula of the compound
First, you must find the smallest whole number ratio of the moles of the elements in the compound
It provides the subscripts for the chemical formula
Empirical formula is the lowest whole number ratio of the elements
CH2O … C2H4O2 … C3H6O3 … C4H8O4 … C5H10O5 … etc.
MOST IMPORTANT FACT
* Empirical formula DOES NOT have to match actual molecular formula
Example: HO is the empirical formula for hydrogen peroxide, H2O2, but HO is not hydrogen peroxide!

12. Empirical Formula
You can assume the mass of the compound is 100 g if they give you percent composition.
So if % is Sulfur (S) and 59.95% is Oxygen (O), then there is g S and g O
Then simply convert to moles:
40.05 g S * 1 mol S = mol S
g S
59.95 g O * 1 mol O = mol O
g O
So the molar ratio is 1.249:3.747 for S:O atoms
This will produce integers but we want whole numbers
How do we simplify?
Take the smaller number and divide it and everything else by that number.
1.249/1.249 = /1.249 = 3
1:3 Ratio so for every one S, there is three O.
SO3

13. Practice Problems Ni: 34.4%, S: 37.5%, O: 28.1%
C: 69.7%, H: 14.0%, N: 16.3%
C: 60.6%, H: 8.14%, P: 31.3%

14. Molecular Formula
Knowing what you know about building compounds, percent composition and empirical formulas…
Realize that hundreds of different substance have the same percent composition and empirical formula
It is possible because they have different molecular formulas
This specifies the actual number of atoms of each element in one molecule or formula unit of the substance

15. Molecular Formula
To determine the molecular formula, the molar mass of the compound must be determined through experimentation and compared with mass represented by the empirical formula
Example: Acetone has a molar mass of g/mol while its empirical formula is CH or g/mol
Since the mass of the molecule is g/mol, divide it by the empirical mass of g/mol
26.04 g/mol / g/mol = 2.00
Thus the molecular formula has to have twice as many carbon and hydrogen atoms than the empirical formula, or C2H2
(Empirical Formula)*n = Molecular Formula