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Chalk Talk
Application
Problem:
How can you determine the number of molecules (formula units) of chalk required to write your
name?
Materials:
one piece of chalk metric
balance
Procedure:
Obtain a piece of chalk from your instructor. Assuming that the composition of the chalk is
calcium carbonate (CaCO3) determine the number of molecules of chalk required to write your
name on the blackboard.
Summing Up:
1. Explain the procedure which you will use in determining the number of molecules of chalk
required to write your name. Be specific!
2. Prepare a data table and record your data and calculations. Be sure to include units on all of
your numbers.
3.
Explain the logic of your calculations. Be specific. Why was each step performed? Is it
necessary to know the number of molecules in 1 mole?
Teacher Notes Chalk
Talk
Application
Lab setup
Calculations
Reliability
Interest
Lab time
Process skills
easy
easy
excellent
excellent
-1 class
Interpreting data
moderate
moderate
good
good
1 class
difficult
difficult
fair
fair
+1 class
Experimenting
Objective;
By completing this activity students will be able to determine the number of molecules (formula units) of chalk
required to write their name.
Teaching Strategies;
If students are not sure how to approach this problem, encourage them to think about the exploratory
activity in which they counted objects indirectly. This should get them started on the right track.
Summing Up;
1. To determine the number of molecules in your name, first weigh a piece of chalk. Write your name on the
blackboard and then reweigh the chalk. The difference in the masses is the mass of chalk required to
write your name. The number of molecules can then be calculated.
2. Sample data table:
Massofchalkbeforewriting=
Massofchalkafterwriting=
Mass of chalk in your name =
Calculations: # of molecules =
6.02 x 1023 molecules
1 mole
X 1 mole X mass of chalk in your name
100 g
3. As can be seen in the above calculations, by canceling out units, the number of molecules of chalk can be
determined. The conversion factor of the number of molecules in one mole is needed to provide the
link betweenthemassofchalkandthenumberofmoleculesinonemoleofchalk.