Moles
Mass
There is also a connection between 1 mole
of a substance and mass of any element or
compound.
 Use Molar Mass to convert between moles
& mass.
 Mass Unit = grams

Moles

Mass
Conversion Factor:
 1 mol = molar mass (grams)
EXAMPLES: Moles to Mass
1.
How many grams are in 5.42 moles of NaCl?
2.
How many moles are in 83.6 grams of H2O?
EXAMPLES: Mass to Moles
3.
How many grams of tin are in 7.9 moles of tin?
4.
How many grams are in 3.34 moles of Na2CO3?
Percent Composition
 The
purpose of
percent composition
is to allow a scientist
to determine the
percent of an
element in a whole
compound.
Example #1
 What
is the percent composition of
chlorine in KCl?
 Step
1:
 Find
the weight of the compound by using
the molar mass
 (1
x 39.098) + (1 x 35.453)
 Molar
Mass of KCl = 74.551 g
Example #1 Continue
 What
is the percent composition of chlorine
in KCl?
 Step
2:
 Find
the weight of the PART you want by
using the molar mass.
 Cl
= 35.453
Example #1 Continue
 What
KCl?
 Step
is the percent composition of chlorine in
3:
 Use the percent composition formula
(MEMORIZE) & round answer to 3 significant
figures.
 Formula:
 Work:
(Part/Whole) x 100
%Cl = (35.453 / 74.551) x 100
 Answer
with correct sig figs: %Cl = 47.6%
Example #2
 What
is the percent composition of
oxygen in KMnO4?
Example #3
 Find
the Percent Composition of Mg in
MgCl2?
Example #4
 What
is the percent composition of each
element in Fe(NO3)3?
Notebook Set Up
Turn to next BLANK LEFT & RIGHT page.
Left Page
Right Page
Chewing Gum
Lab
Moles to
Mass/Percent
Composition
Student Notes
Notebook Set Up
Turn to next BLANK LEFT & RIGHT page.
Left Page
Mole
Worksheet #3
Right Page