What is a mole in chemistry?
The SI unit for measuring the
____________________________
____________________________
What is Avogadro’s Number?
The atomic mass of one atom of
carbon-12 is 12 amu.
Avogadro found that ___________
of carbon-12 had ______________
The unit symbol is _____________
atoms.
__________________ became
One mole is equal to
____________________________
known as ____________________
____________________________
which equals one mole!
____________________________
That works for everything!
Since particles of matter are so
small, we can’t count them even if
we could count that high.
If we have one mole of calcium,
how many atoms of calcium do we
have?
Moles are used to convert mass in
_________________ to
____________________________
If we have 6.02x1023 atoms of
potassium, how many moles do we
have?
Particles of Matter
Particles of Matter continued
Particles of Matter continued
Formula Unit: Representative
Atom: Representative particle of
Molecule: Representative particle
particle of ___________________
____________________________
of __________________________
____________________________
____________________________
____________________________
Formula units are described by
Atoms are indicated by an
Molecules are described by
____________________________
____________________________
____________________________
Examples:
Examples:
Examples:
NaCl represents one formula unit
of ________________________
commonly called table salt.
H2O represents one water molecule
Ion: Representative particle of

How many H atoms?

How many O atoms?

How many total atoms?

How many atoms of Na?

How many atoms of Cl?

How many total atoms?
____________________________
____________________________
Ions are indicated by an
____________________________
____________________________
Na(HCO3) represents one formula
C12H22O11 represents one sugar
molecule

How many C atoms?

How many H atoms?

How many O atoms?

How many total atoms?
Examples:
unit of ______________________
common name is baking soda.

How many Na atoms?

How many H atoms?

How many C atoms?

How many O atoms?

How many total atoms?
How to Determine Molar Mass
Molar mass of an element is ________________
___________________________ of the element
from the periodic table, but the units are different.
The unit for molar mass is _____________________

The molar mass of potassium is ______________
zinc is __________________________________
Oxygen can be rounded to __________________
Molar mass of a compound requires a ____________
_________________; this is often called formula
mass.

The mass of _________________________ in
the formula is _____________ together in the
ratios as of the _____________________; the
unit is in _____________________________.
Let’s do examples inside using the mole map!
3) Find the empirical formula of the compound by finding
the ratio of the number of moles of elements.
How are molecular and empirical formulas determined from a
percent composition calculation?


An empirical formula is a chemical formula with the lowest
whole-number ratio of elements in a compound.

A molecular formula is the actual chemical formula of a
compound.

Review: Empirical formulas are reduced versions of the
molecular formula. In a practical sense, this means that we
should divide the number of moles of each element by the
smallest answer for number of moles. Since the smallest
number is “7.14 moles”, we’ll divide both values by 7.14.
carbon:
7.14 ÷ 7.14 = 1
hydrogen: 14.3 ÷ 7.14 = 2
Empirical formulas are reduced versions of the molecular
formula. For example, a compound that has an empirical
formula of CH2O may have a molecular formula of C2H4O2,
C3H6O3, C4H8O4, etc.

Empirical formula:

Handy hint: If the problem gives you the empirical
formula, you can start at the next step!
Steps 1-3 for Calculating Empirical Formulas and Steps 4-5 for
Calculating Molecular Formulas
4)

Once you have a percent composition of a chemical compound,
it’s possible to figure out the molecular formula. Here’s how,
using the example of a compound with a molar mass of 28
grams/mol in which the percent composition of the components
are as follows:
o C: 85.7%
o H: 14.3%
1)
Assume you have 100 grams of the chemical. This serves to
convert the percentages into grams.
5)
Divide the molar mass of the compound in the problem by
the molar mass of the empirical formula.

For our compound, the molar mass of the compound is

For the empirical formula, CH2, the molar mass is

Divide as instructed in step 4 above
Multiply the subscripts in the empirical formula by the
number you found in step 4 to find the molecular formula.
In our example, we now have
2)
Figure out how many moles of each element you have in the
compound.
NOTE: Sometimes the empirical formula and molecular formula are
the same.
What does the percent composition of a
compound represent, and how is it calculated?

The percent composition of a compound
represents the percentage of each element in a
compound by mass.
o

Percent composition is calculated by dividing the
mass of a single element in one mole of a
compound by the molar mass of the compound
and multiplying by 100 to make a percentage.
o
Example using water, what is the percent
composition of H and O?
o
o
H2 mass
o
O mass