1. Chemical Composition

2. Chemical Composition
The identities, and relative numbers, of the elements that make up any particular compound
Example: H2O
H – Hydrogen
2 atoms
O - Oxygen
1 atom

3. Counting Atoms by Grams
Atoms are extremely small so we use a larger number
Mole (mol) = x 1023
Avogadro’s number
Can specify a mole of anything
Example: Atoms, Ions, Molecules

4. Conversions How do we convert from atoms to moles???
1 mol = x 1023 atoms
Example:
You have 3.5 moles of helium. How many atoms do we have?

5. Molar Mass Molar Mass Example of Molar Mass of Elements
The mass of 1 mol of atoms of an element
This number is equal to the element’s atomic mass in atomic mass units
Example of Molar Mass of Elements
Copper
Atomic Mass of amu
Therefore, 1 mole of copper atoms has a mass of g/mol

6. Conversions cont. How do we convert between Grams and Moles? Example:
Calculate the number of moles of sulfur in 57.8 g of sulfur.
Conversion factor: 1 mol S = g S
Therefore:

7. Finding Atoms
How many aluminum atoms are there in an aluminum can with a mass of 16.2 grams?
Conversion Factor:
26.98 g Al = 1 mol Al
1 mol Al = x 1023 Al atoms

8. Molar Mass of Compounds
To calculate the molar mass:
Add the masses of each element of the compound to get the total
Example:
CO2
Carbon – g
Oxygen – g
Therefore:
12.01 g + 2(16.00g)
44.01 g

9. Conversions cont.
How do we convert between grams and moles of a compound?
1. Calculate the molar mass of the compound
2. Find conversion factors
3. Solve

10. Example Calculate the mass (in grams) of 1.75 mol of water.
Molar Mass of H2O = 2(Atomic Mass of H) + 1(Atomic Mass of O)
= 2(1.01g/mol) + 1(16.00g/mol)
= g/mol