Mr. Chapman
Chemistry 20
Converting from grams to moles
Need: Moles and Mass worksheet.

To convert from grams to moles,
we multiply the number of grams
by the molar mass of the
compound or element.

To convert from moles to grams,
we multiply the number of moles
by the molar mass of the
compound or element.
EVERY MOLE OF SODIUM
HAS A MASS OF 22.990 g.
22.990 g of SODIUM
CONTAINS 6.022x1023
atoms of sodium

An empirical formula of a compound is the smallest,
whole number ratio of atoms in a compound.

For example, the molecular formula for glucose is
C6H12O6. The empirical formula for glucose is CH2O.

We can find the empirical formula for a compound if
we know the mass percentage of each element in
the compound.
1.
Find the empirical formula of a compound
that is 48.38% carbon, 8.12% hydrogen, and
53.5% oxygen by mass.
Note: As with most stoichiometry problems (which
we will learn about), it is necessary to work in
moles. The ratio of the moles of each element
will provide the ratio of the atoms of each
element.

Get the mass of each element by assuming a
certain overall mass for the sample (100 g is a
good mass to assume when working with
percentages).

Convert the mass of each element to moles of
each element using the atomic masses.

Find the ratio or the moles of each element by
dividing the number of moles of each by the
smallest number of moles.

Use the mole ratio to write the empirical
formula.

What is the empirical formula of a compound
that is 75% carbon and 25% hydrogen?