At the end of the lesson students should be able to:
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.
This lesson can be completed in one extended block.
The lesson starts with a challenge question which the students will answer at the end of the lab as a check out exercise.
Your favorite game store is running a contest where you must guess the number of Acme brand candy corn pieces that are in a sealed fish bowl. You only have 20 minutes before the contest ends, and the owner says you can do anything except open the bowl. The store next door is a general store that carries normal household items and the same fish bowl and candy corn. Create a procedure that lets you determine the number of candy corn in the bowl without counting them manually. (There just isn’t enough time!)
Average mass of small paper clip = mass of 20 small paper clips – mass of plastic tray / 20
(Calculated mass of small paper clips – Actual mass of small paper clips / Calculated mass of small paper clips) X 100.
Record this number on your data chart in the appropriate column. Students will notice that the actual mass is very close to the calculated mass and that it was much quicker to calculate the mass than to count out 100 paper clips and weigh them.
(100 – Actual number of small paper clips / 100) X 100.
Record these numbers on your lab sheet in the appropriate column. Students will notice that this quicker method is still fairly accurate.
Given the time and materials, a good tie in to a robotics program might be for the students to design and execute a robot to count out metal BBs or a simular product.
Now ask the students to answer the challenge question and turn the answer in as an "exit ticket."
Your favorite game store is running a contest where you must guess the number of Acme brand candy corn pieces that are in a sealed fish bowl. You only have 20 minutes before the contest ends and the owner says you can do anything except open the bowl. The store next door is a general store that carries normal household items and the same fish bowl and candy corn. Create a procedure that lets you determine the number of candy corn in the bowl without counting then manually. (There just isn’t enough time!)
Sample Lab Report Questions
John Tracey, teacher of physics and chemistry, currently at Mount Olive High School
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