Notebook Setup
Assignment
Mass and the Mole CORNELL notes
Moles to Mass Example &
Mass to Moles Example
Mass to Atoms & Atoms to Mass Examples
Calculations Involving the Molar Mass of an
Element handout
Page
Number
51
52
53
54
Mass and the Mole
Learning Objectives
Relate the mass of an atom to the mass of a
mole of atoms.
Convert between number of moles and the
mass of an element.
Convert between number of moles and
number of atoms of an element.
Introduction
• Do eggs come in different sizes?
• Does the size of the eggs affect how many you
get if you buy a dozen eggs?
• A dozen always contains the SAME number of
eggs but a dozen eggs will have different
masses depending on the size of the eggs.
Introduction
• Does a dozen limes have the same mass as a
dozen eggs?
• Because eggs and limes differ in size and
composition, they have different masses.
NOTES START HERE
• For the same reason, one-mole quantities of two
different substances have different masses.
– Example: one mole of carbon and one mole of copper
have the SAME number of particles but different
masses
Molar Mass
• Molar mass is the mass in grams of one mole
of any pure substance.
• The molar mass of any element is numerically
equal to its atomic mass and has the units
grams/mol.
• The mass of an atom is also equal to the mass
in grams of one mole of the element.
Conversions Involving Mass
Real World Problem
• Imagine that our class bought jelly beans in
bulk to sell by the dozen at a candy sale. We
soon realize that it is too much work to count
out each dozen, so we decide to measure the
jelly beans by mass. We find that the mass of
1 dozen jelly beans is 35 g.
• What mass of jelly beans should you measure
if a customer wants 5 dozen jelly beans?
Problem Setup
1. Write the given and needed units.
2. Write a unit plan to convert the given unit to the
needed unit.
3. Write conversion factors that connect the units.
4. Set up the problem. Use conversion factors to
cancel the given unit and provide the needed
unit.
5. Calculate the answer. Multiply numbers that are
across from one another and divide numbers
that are underneath.
Real World Problem
Step 1: known 5 dozen
unknown # of jelly beans
1 dozen = 12 roses
Step 2: dozen  # of jelly beans
Step 3:
1 dozen = 12 jelly beans
1 𝑑𝑜𝑧𝑒𝑛
12 𝑗𝑒𝑙𝑙𝑦 𝑏𝑒𝑎𝑛𝑠
Step 4:
Step 5:
5 dozen
or
12 𝑗𝑒𝑙𝑙𝑦 𝑏𝑒𝑎𝑛𝑠
1 𝑑𝑜𝑧𝑒𝑛
12 jelly beans
1 dozen
60 jelly beans
Moles to Mass Example
Calculate the mass in grams of 0.0450 mol chromium
(Cr).
Mass to Moles Example
How many moles of calcium (Ca) are in 525 g Ca?
Mass to Atoms Example
How many atoms of gold are in a U.S. Eagle, a gold
alloy bullion coin with a mass of 31.1 g Au?
Atoms to Mass Example
A party balloon contains 5.50 x 1022 atoms of helium
gas. What is the mass, in grams, of the helium?
Summary
• The mass in grams of one more of any pure
substance is called its molar mass.
• The molar mass of an element is numerically
equivalent to its atomic mass.
• The molar mass of any substance is the mass in
grams of Avogadro’s number of representative
particles of the substance.
• Molar mass is used to convert from moles to
mass. The inverse of molar mass is used to
convert from mass to moles.