This document provides instructions for a lab experiment on determining the number of moles of chalk used to write a student's name. The purpose is to review the mole concept and introduce proper lab report writing. Students are instructed to weigh a piece of chalk before and after writing their name, calculate the mass of chalk used, and determine the number of moles of calcium carbonate. The lab report sections include the purpose, hypothesis, materials, procedure, results, analysis, calculations, and conclusion.

1. Name: ________________________
Moles of Chalk Lab
This lab is designed to help you review the concept of the mole which
will be on your upcoming test, but it is also an introduction to how I
expect you to write up lab reports for future labs we will be doing the
second half of the year.
Purpose: The purpose section of a lab is where you tell the reader your reason
for doing the lab in the first place. For example, many researchers for
drug companies have as their purpose that they want to cure AIDS or
some other disease. This section should be three or four sentences long.
If it’s too short, it won’t be clear why you’re doing the lab. If it’s too long,
you’re doing too much work and the reader will probably just skip over it.
Write your purpose: ________________________________________________
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Hypothesis: If _____________, then _______________. (The hypothesis is a
one-line sentence where you discuss how you’ll solve the problem at
hand. The statement after “if” is the independent variable. The
independent variable is whatever you’ll do to solve the problem. The
statement after “then” is the dependent variable, because what happens
will depend on what you did in the first place. Generally, the dependent
variable will be that the problem you mentioned in the purpose will be
solved.)
Write your hypothesis: ______________________________________________
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Materials: Your materials list must be VERY complete. You need to indicate
how much of each material will be used in the experiment so you know
what you’ll need. If you plan on arranging some of the equipment into a
more complex setup (for example, if you’re going to heat something over
a Bunsen burner, you’d need a ring stand, wire gauze, etc.), draw it as
well as mentioning the equipment used. It’s never a bad idea to leave a
couple of extra lines at the end of this section so you can add more things
that you’ve forgotten when you started your lab.
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2. Write your materials: _______________________________________________
________________________________________________________________
Procedure: This is a very clear, step-by-step list of things you plan on doing
during the experiment. Each step should be short (one phrase or
sentence). Again, it’s not a bad idea to leave a few blank lines at the end
of this section to add things that you may have forgotten.
Your procedure: Weigh a piece of ordinary chalk and write your name
on the blackboard. Weigh the chalk again, and determine the
number of moles of calcium carbonate that were used.
Results: This is the section where you write down all of your raw data. It should
consist of quantitative (numerical) data arranged in charts, as well as
qualitative (non-numerical) data written out as sentences. The results
section will most likely be long, so make sure you leave plenty of room. A
good rule of thumb when writing the results section is that if you’re not
sure if what you’ve seen is a result, write it down. Your results section
can never be too long!
Weight of chalk before writing your name: _______________
Weight of chalk after writing your name: _______________
Grams of chalk required to write your name: _______________
Molecular weight of calcium carbonate: _______________
Analysis: This is where you explain the meaning of your results. If you need to
make a graph or a chart, use the data you took in the results section to
make the proper charts here. If you need to explain why something
happened, you need to write it here. If calculations are required, they
belong here. The analysis section is the part of a lab where you explain
why your hypothesis is right or wrong, based on the data you’ve taken.
Like the results section, if you’re in doubt about whether or not to write
something here, include it!
Calculations (be complete!):
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3. I needed _______________ moles of calcium carbonate to write my
name on the blackboard.
Conclusion: The conclusion section needs to have the following:
• A one-line sentence that either says that the hypothesis is right or the
hypothesis is wrong. For example, if you proved the hypothesis that “If I poke
myself in the eye, then my eye will hurt”, this first sentence would be “When I
poked myself in the eye, it hurt.”
• If the hypothesis didn’t work, an explanation of what you think went wrong.
These should be specific suggestions (I should have heated the mixture to
550 C), not general suggestions (I should have heated it more).
• A brief error analysis section. You should list at least two things that could
have caused errors in the lab as well as ways you can prevent those errors in
the future. The errors you mention should be errors that you can do
something about, not mystical errors that probably didn’t happen.
Write your conclusion: ______________________________________________
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4. Moles of Chalk Lab – Teacher Materials
Materials:
• One piece of chalk for each student (these can be reused from class to
class)
• As many balances as you can find
Doing the lab:
Students really enjoy this lab because it’s easy to do and easy to conceptualize
what’s going on. There’s not really much to doing the lab, as the instructions are
listed on the student handout page.
Grading this lab is pretty easy – if I were you, I would just check to make sure
that the students put the weights of the chalk before and after writing their names
in the appropriate blanks (including units). To grade whether they got it right or
not, I’d just check to see if the final answer was right – if it is and they’ve shown
some work, it’s probably safe to assume that they know what they’re doing. If
they get the wrong answer, go back and check their work to assign partial credit.
If they get the right answer but don’t show their work, give no credit for their
answer, whether it’s right or wrong!
Because the molar mass of calcium carbonate is 100. g/mol, the number of
moles of calcium carbonate will be equal to the mass of chalk used to write their
names divided by 100. For example, if it took 0.500 grams of chalk to write their
name, the number of moles of calcium carbonate used would be 0.500 g / 100. g/
mol = 0.00500 mol. As you might imagine, answers will vary depending on how
hard the student writes, the length of their name, etc.
Modifications:
• Many classrooms use dry-erase boards rather than chalkboards. If this is
true where you live, you may want to try using “sidewalk chalk” and have
them write their name on the pavement outside. Sure, it sounds a little
childish, but kids seem to really enjoy it.
• A bad modification to this lab is to extend it so students calculate the
number of “molecules” of calcium carbonate as well as the number of
moles. Ionic compounds don’t exist as discrete molecules, making this
modification scientifically invalid.
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