1. FORMULA MASS

2. 17.2 Conservation of mass
Lavoisier showed that a closed system must be used when studying chemical reactions.
When chemicals are reacted in a closed container, you can show that the mass before and after the reaction is the same.

3. 17.2 Formula mass
The sum of the atomic mass values of the atoms in a chemical formula is called the formula mass.

4. Atomic & Molecular Weights
Chemical formulas and chemical equations have quantitative significance. H2O means 2 atoms of hydrogen and 1 atom of oxygen. C3H8 + 5O2 → 3CO2 + 4 H2O means 5 moles of oxygen gas

5. Definitions:
Molecular Formula: the actual number of atoms of each element in the compound.
Molar mass: the mass of one mole of any substance
Atomic mass unit: amu
The number of amu’s in formula mass = molar mass in grams

6. 17.2 Molar Mass

7. Example Formula mass CaC03 = 100.09 amu 1 mole CaC03 = 100.09 g CaCO3
Which is the Molar Mass

8. 17.2 Avogadro’s Number
The Avogadro number was named in honor of Amedeo Avogadro who discovered that a mole of any gas under the same conditions has the same number of molecules.
Johann Josef Loschmidt, a German physicist, named and discovered the Avogadro number.
Loschmidt realized that a mole of any substance—be it a gas, liquid, or solid—contains 6.02 x 1023 atoms or molecules.

9. Avogadro’s Number
Avogadro’s number states that for one mole of any substance, whether element or compound, there 6.02x1023
particles present in the sample.
It is also the number of molecules in the formula mass of a compound when these masses are expressed in grams.
One set of 6.02x1023 atoms or molecules is also referred to as a mole of that substance.

10. Remember 1 gram = x1023 amu The atomic mass unit(amu) is assigned by assigning exactly 12 amu to the 12C isotope

11. 1 oxygen atom = 16.0grams
1mole of oxygen atoms=6.02x1023atoms=16.0grams
What Is a Mole?

12. Formula Weight & Molecular Weight
Formula Weight – Ionic Compounds Molecular Weight – Molecular/Covalent Compounds ****We tend to use interchangeably**** To find the Formula/Molecular Weight Simply find the sum of the atomic weights of each atom in the compound.