Moles, Moles, Moles

Patricia A. Riley Lincoln Park High School
2001 N. Orchard Street Mall
Chicago IL 60614
(312) 534-8130 ext. 148

Objectives:

By the end of this lesson, 10th grade students will be able to:
1. define a mole and 2. measure out a mole by mass or volume.

Materials:

Teacher demonstration:
colored dot sticker
various stuffed moles, including one that can be ripped in half
cardboard mole labeled with "1 mole = 6.02 x 1023"
paper clips
test tubes each containing 1 mole of a common substance: Aluminum wire,
iron filings, water, sodium chloride (NaCl), etc.

Each pair of students:
60 paper clips solid aluminum blocks
balance metric ruler

Strategy:
1. Teacher has a sticker on her cheek and cuddles a stuffed mole in her
arms.
2. Write the word "mole" on the chalkboard. Ask the students what it
means. As students suggest the animal, toss the stuffed mole to the
side and say that is not a chemistry mole. Rip off the sticker and
throw it away when they mention the beauty spot/skin blemish. Compare
the chemistry mole to a dozen. Explain that it represents a set group
of things, 6.02 x 1023, just as a dozen is 12 things. Write this
value on the board both in scientific notation and expanded to show all
the zeros. Lean the cardboard mole against the chalkboard.
3. Scatter 36 paper clips on an overhead projector and ask a student to
come up and count them. Emphasize that a dozen is a method of counting
and grouping objects. Pick up three stuffed moles and explain that just
as you can have three dozen paper clips, so you can have three moles of
paper clips. Change the number of paper clips on the overhead to 42 and
repeat the exercise. Point out that there can be fractions of a mole.
Pick up a fourth stuffed mole that can be ripped in half and suddenly
rip it apart, while telling the class that there can be fractions of a
mole as well.
4. Hold up a test tube containing one mole of aluminum wire and ask the
class how many atoms of Al are in the tube. Hold up a test tube with
one mole of H2O and ask how many molecules of H2O are in the tube.
Repeat with the other test tubes. Remind the class that a mole is a
fixed number of things just as a dozen is.
5. Give each pair of students a bag of sixty paper clips. One student is
to count the paper clips as quickly as possible, while the other records
the time in seconds. Write the times on the chalkboard and then have
the students average them. Ask the students how long it would take them
to count out a mole of paper clips, helping them set up the proportions:

60 paper clips 6.02 x 1023 --------------- = ------------ recorded time X seconds and then solve for X. Have them then convert this answer into minutes, hours, days, and finally years; do not forget that a year is actually 365.25 days long, hence Leap Year. Is it reasonable to count out a mole of paper clips? Of anything? No! 6. Hold up the test tube containing a mole of aluminum atoms and tell the class that you only needed five minutes to put the mole of atoms into the tube. Repeat with the other tubes. How could this be done? Remind the class that the average atomic mass of an atom of each element is listed in the Periodic Table. Explain that a mole of each atom happens to have that same mass in grams. This is true since atomic masses are a comparison of each atom to the standard carbon-12 atom: Example: If 1 carbon-12 atom 12.00 amus ---------------- = ----------- 1 hydrogen atom 1.0079 amus then as long as we have equal numbers of each atom, the ratio of their weights must be the same. One mole of carbon-12 atoms just happens to weigh 12.00g, so one mole of hydrogen atoms must weigh 1.0079 grams: 6.02 x 1023 carbon-12 atoms 12.00 grams
--------------------------- = -------------
6.02 x 1023 hydrogen atoms 1.0079 grams

Ask again how to get a mole of aluminum atoms into a test tube in five
minutes. Answer: weigh it out! How much does a mole of Al weigh?
Have the students check the periodic table. Repeat with other familiar
elements.
7. Give each pair of students a solid aluminum block and a metric ruler.
Have them measure the length, width, and thickness and then calculate
the volume. What would be the volume of a mole of such blocks? What
assumptions would we have to make about the blocks in the mole? Could
we possibly use volume to measure out a mole quickly? Yes. The problem
is what is the volume of one atom of each element? Hold up any two of
the test tubes each of which contains a mole of a substance and have
students note the differences in the volume. Have them examine the
Periodic Table for atomic volumes; they are not listed.
8. Which method is easiest then for measuring out a mole: counting,
weighing, or using the volume? Take your pick!

Performance Assessment:
Each pair of students will be given a sample of copper, nickel, tin,
sulfur, or silicon and told that they have 10 minutes in which to measure out a
mole of their element. All samples will be in either pellet or powder form.
Students will have a balance, a metric ruler, a periodic table, weighing paper,
and spatula to work with. They must measure out their mole, show the teacher
the mole as it sits on the balance or metric ruler, and then write a brief
description of the method they used.