Molecular/Formula Mass
The molecular mass is the atomic mass of all atoms within a molecule. The formula
mass is specific to ionic compounds. We will be using this molecular mass when
talking about the mole in later sections. To find the molecular mass, (or formula
mass in the case of ionic compounds..) we simply take the amount of atoms within
the compound for each element, and multiply that amount by the atomic mass of
that element.
Example: HC2H3O2 (acetic acid)
To calculate the molecular mass, we break the molecule into the individual elements
to see how many atoms of each element we have.
H-4
C-2
O-2
We then multiply that amount by the atomic mass of that element. You do not need
to use the entire atomic mass from the periodic table, the general rule is going two
past the decimal.
H-4(1.01amu)= 4.04 amu
C-2(12.01 amu) = 24.02 amu
O-2 (16.00 amu)= 32.00 amu
Now that we have the atomic mass of each individual part, we can add all parts
together to get the atomic mass of the molecule.
4.04amu + 24.02 amu + 32.00 amu = 60.06 amu
This value gives us the molecular mass for acetic acid. When we talk about this in
terms of the mole, we will call this value the molar mass. The molar mass of a
molecule is simply its total atomic mass, but instead of using the atomic mass unit,
we use the unit of grams to equate this value to a mole.
Use this example and the material covered in class Tuesday January 13th and
Wednesday January 14th to complete this blizzard bag assignment.