1. Objectives
To understand the definition of molar mass
To learn to convert between moles and mass
To learn to calculate the mass percent of an element in a compound

2. A compound is a collection of atoms bound together.
A. Molar Mass
A compound is a collection of atoms bound together.
1 mole of methane
1 mole of carbon and 4 moles of hydrogen
The molar mass of (“one mole of”) a compound is obtained by summing the masses of the appropriate number of moles of component atoms.

3. A. Molar Mass
For compounds containing ions the molar mass is obtained by summing the masses of the component ions. This is sometimes called the formula weight.

4. What is the Molar Mass of the following Compounds?
Na3N CS2 NH4Br C2H5OH H2SO3 H2SO4 MgSO4

5. A. Molar Mass
Calculations Using Molar Mass
Moles of a compound (g) =
Mass of a sample (g) = moles of sample (mol) x molar mass of compound (g/mol)
Number of atoms in moles of a sample = number of moles x number of atoms in formula x Avogadro’s number

6. Relationships Between Moles, Mass and Atoms
Avogadro’s Number 6.022x1023
Atomic Mass from Periodic Table
Moles
Atoms
Mass

7. Relationships Between Moles, Mass, Molecules and Atoms
Molar Mass using Periodic Table
Avogadro’s Number 6.022x1023
Molecules
Moles
Mass
Atoms
Molecular Formula

8. B. Percent Composition of Compounds
Percent composition consists of the mass percent of each element in a compound:
Mass percent =
What are the mass percentages of C, H and O in Ethanol?

9. Calculate the Mass Percent of These Compounds
LiBr CuOH SrSO4 C2H4O C6H12O6