1. Flashback
In your notes … answer the following question to the best of your ability:
1.) How many atoms would there be in one mole?
2.) What would be the mass of one mole of Carbon atoms?
3.) What would be the mass of 2 moles of H2O?

2. The Mole By: Ms. Buroker Microscopic world of atoms
Macroscopic world of the lab
The Mole
Honors Chemistry:
Section 3.3 & 7.4 in your book!

3. What is the Mole? * commonly abbreviated mol
The mole is the SI base unit used to measure the amount of a substance.
* commonly abbreviated mol
The mole can be defined as the number equal to the number of carbon atoms in grams of carbon.

4. Avogadro’s Number
One mole of something consists of x 1023 units of that substance. 1 mol = x 1023 particles
Molecules
Formula Units
(Ionic Compounds)
Atoms

5. Average atomic mass of this element Number of atoms in this sample
1 mole of any element has a mass in grams that is equal to its average atomic mass
Silver (Ag)
Lead (Pb)
Average atomic mass of this element
107.9 amu
207.2 amu
Mass of this sample
107.9 g
207.2 g
Number of atoms in this sample
6.022 x 1023 atoms

6. Molar Mass
The molar mass of an element is the mass in grams of one mole of any pure substance.
At this point, we need to make sure you can easily go back and forth between moles, grams, and particles.
Example:
Molar Mass of Nitrogen is equal to the atomic mass in grams… 14.00g.

7. Formula Weight or Molecular Mass
The molar mass of an ionic compound or molecule is equal to the sum of the mass (in grams) of the elements involved.

8. Mole Relationship and Compounds
A chemical formulas tell us the number of atoms that make the compound … but, it can also tell us something about the number of moles of atoms in the compound!
For example: CaCl2
1 calcium atom
In 1mol of CaCl2, there is 1mol of calcium
2 chlorine atoms
In 1mol of CaCl2, there are 2moles of chlorine

9. Let’s Practice!!
Determine the number of moles of chloride ions in 2.50mol ZnCl2
5.00mol Cl-
Calculate the number of moles of each element in 1.25mol glucose (C6H12O6)
7.50mol C
15.0mol H
7.5mol O

10. Some Vocabulary …
Percent Composition: The percent by mass of each element in a compound.
Empirical Formula: The formula with the smallest whole number ratio of the elements.
Molecular Formula: The formula which specifies the actual number of atoms of each element in one molecule or formula unit.

11. Percent Composition Mass of element Mass of compound X 100 = Examples:
Percent by
Mass
Mass of element
Mass of compound
X 100 =
Examples:
Sodium hydrogen carbonate, also called baking soda, is an active ingredient in some antacids used for the relief of indigestion. Determine the percent composition of sodium hydrogen carbonate.

12. EMPIRICAL FORMULAS Example: Hydrogen peroxide empirical formula: HO
Empirical formulas may or may not be the same as the molecular formula …
Example: Hydrogen peroxide
empirical formula: HO
molecular formula: H2O2

13. How Do I Find the Empirical Formula?
1.)Find the number of moles of each element.
* If given percent composition- assume g
2.) Calculate the simplest ratio of moles of the elements by dividing each number of moles by the smallest whole number ratio.
* If the number are not whole, then multiply by the smallest number that will produce a ratio of whole numbers.

14. Multiply the numbers in the empirical formula by the value of “n”
MOLECULAR FORMULAS
Experimentally determined molar mass
Mass of Empirical Formula n =
Multiply the numbers in the empirical formula by the value of “n”
Molecular formula = (empirical formula) n