Each group of students will relate the time and effort required to count out by hand a large number of small objects to the time and effort required to count the same sample using only the mass of the sample. The group will then be asked to determine the number of objects in a different sample as a check in exercise. The students can then apply what they have learned in the lab to solve the challenge question that was posed at the beginning of the lab.
How does this relate to atoms, atomic weight, molar mass and moles?
Each atom has an average atomic weight. This is the decimal number on the periodic table. The average mass of a paper clip is like the atomic weight of an atom.
To get the average mass of a compound, chemists add up the atomic weights of the individual atoms. For example, water has a formula of H2O. One mole of water has the mass of the mass of two hydrogen atoms and one oxygen atom.
Water = 18 g/mole = 1 Hhydrogen (1 g/mole) + 1 Hydrogen (1 g/mole) + 1 Oxygen (16 g/mole)
I can tell how many moles of water I have by determining the mass of the water and then dividing by the mass of one mole. Therefore 180 grams of water would be 10 moles of water.
180 grams / 18 grams/mole
There are many tutorials available on the internet. One you can check out is:
An interesting site that is also worth checking out is:
Before implementing this lesson, you should figure out the average mass of one large paper clip. You will provide this number to students in Step 9 of the procedure.