Chemistry
The Mole: MAC NOTES:






The mole is the base unit in the metric system to measure the amount
of a substance.
Conversion factors are equalities with different units; they can be
inverted, based on the needs of a problem.
Avogadro’s conversion factor, 1 mol./6.02 X 1023 particles, is used to
change from moles to a particle count and vice versa. Common
particles in chemistry are atoms, ions, molecules, formula units.
The molar mass conversion factor, 1 mol./grams of a pure
substance—either as an element or compound—is used to change
from moles to mass in grams and vice versa.
The two conversion factors can be used together to solve problems
starting with particles and ending in mass and vice versa.
Number sense: Molar mass values are rounded to the hundredths
place; most final answers have three significant digits; don’t forget 1
your units and labels when working problems!
Chemistry
The Mole: MAC NOTES:
Determining the Molar Mass of Compounds:




Step ONE: Determine the molar mass of each element
in the compound using a periodic table (average atomic
mass in grams, rounded to the 100th place).
Step TWO: Multiply this molar mass per mole by an
element’s subscript the if there is more than one mole
(a subscript applies to the element to its LEFT)
Step THREE: Use a subscript OUTSIDE a bracketed part
of a chemical formula as a multiplier of the number of
moles for each element INSIDE the bracket only.
Step FOUR: Sum the molar masses of each element. 2
Chemistry
The Mole: MAC NOTES:
Determining Percent Composition:

Step ONE: Find the molar mass of the compound.
Step TWO: Calculate the mass of EACH element in the
compound.
 Step THREE: Divide the mass due to each element by the
total molar mass of the compound and multiply by 100.

Determining Chemical Formulas:
 An
empirical formula is the smallest whole-number ratio of
moles that make up a compound.
 A molecular formula is the actual whole-number ratio of
moles that make up a compound. They can be the SAME.
3
Chemistry
The Mole: MAC NOTES:
Determining Chemical Formulas CONT.:
 An
1.
2.
3.
A
1.
2.
3.
empirical formula determination:
Convert percentage or mass date per element in the compound
into moles using the molar mass conversion factor.
Divide all mole values by the smallest of the mole values.
If the resulting moles per element can NOT be rounded—such as
0.25; 0.33; 0.50; or 0.75—then use an appropriate multiplier of all
mole values (i.e, 2, 3, or 4) to make ALL whole numbers.
molecular formula determination:
Determine the molar mass of the empirical formula.
Divide the molar mass of the molecular formula (a given) by the
molar mass of the empirical formula to get ‘n’ (a multiplier).
Use ‘n’ to multiply the empirical formula subscripts by to get the
actual number of moles for each element in the compound.
4