With a partner weigh a piece of ordinary chalk on an electronic lab balance. Record the mass to the nearest 0.001 g. Use that same piece of chalk to draw a picture appropriate to decorate the room. Weigh the chalk again and determine the number of moles of calcium carbonate that were used. (Chalk is the chemical compound called calcium carbonate).
Weight of chalk before drawing: _______________
Weight of chalk after drawing: _______________
Grams of chalk required for your drawing: _______________
Chemical formula of calcium carbonate: _______________
Molar mass of calcium carbonate: _______________
Moles of chalk required for your drawing: _______________
Calculations (be complete!):
I needed __________ moles of calcium carbonate for my drawing.
Write this result on the bottom edge of your drawing along with your names. Then tell your teacher you're ready to hang it up. Each individual student must hand in this sheet with correct calculations to receive credit for this lab.
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General Chemistry Moles of Chalk Lab - Teacher Materials
One piece of chalk for each student (these can be reused from class to class)
As many balances as you can find, with the best precision available.
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, grade according to your usual method of dealing with such things.
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.
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. If you don't feel comfortable with letting the kids outside, you can also have them write their names on the back of their lab sheet.
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. It is valid to modify the lab so that students calculate the number of ions present in their names, but I'm not sure why you'd want to.