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More Class Lessons for Chemistry Topics 2000
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What Weighs More, An Ounce of Feathers or An Ounce of Gold? An Introduction to Conversions and Dimensional Analysis
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Summary:
The prepared PowerPoint presentation prompts students through a simple exercise identifying conversion factors and applying basic dimensional analysis to solve a problem.
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Grade Level: 10,11
Curricular Area:
Chemistry
Class Time Required:
This can be used as an opener or extended to one class period. (Estimated)
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| Standards: |
As described under the California Content Standards for Chemistry, students are to know and understand how to convert between units as needed to perform stoichiometry calculations. This is listed under item 3. Conservation of Matter and Stoichiometry which details that students know "how to determine molar mass of a molecule from its chemical formula and a table of atomic masses, and how to convert the mass of a molecular substance to moles, number of particles or volume of gas at standard temperature and pressure." To provide students with the skills to do such calculations, an understanding and practice of conversion between units and dimensional analysis should be mastered.
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| Learning and Teaching Activities: |
There is generally an extremely broad variety of pre-knowledge and experiences with basic mathematical conversions and dimensional analysis among both beginning Honors and Regular Chemistry students. These skills are basic and necessary for success in chemistry and require practice in a variety of scenarios. In the opener "What Weighs More, An ounce of feathers or an ounce of gold?" students will be aided in identifying equalities, writing them as conversion factors and applying these factors to a simple dimensional analysis problem.
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| Outcomes and Assessment: |
Upon completion of this initial activity, students will be able to successfully demonstrate an understanding of simple unit conversions first by identifying equalities, then by writing them as conversion factors and finally by applying these factors to simple dimensional analysis to solve a given problem. A dowloadable, follow-up handout with prompts to guide students in solving a second problem will be made available as soon as possible.
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| Materials Needed: |
| Computer, Internet access, Powerpoint software, LCD projector or a simple overhead projector
Powerpoint Presentation: "What Weighs More: An Ounce of Feathers or An Ounce of Gold?"
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| Resources: |
Resource 1
Resource 2
Resource 3
Resource 4
Resource 5
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| Opening: | Opening my Chemistry Program each fall, I find an extremely broad variety of pre-knowledge and experiences with basic mathematical conversions among both my Honors Chemistry and Regular Chemistry students. I HATE to drag on and on with boring math computations, conversions, and dimensional analysis with little application in an attempt to level the playing field with skills needed for basic chemistry.
In defense I developed a couple of applications that turned out to be great fun, which began as the simple opener "What Weighs (hate to use this term) More, An Ounce of Feathers or An Ounce of Gold?" This was a rather contrived but interesting conversion and dimensional analysis application using troy ounces versus avoirdupois ounces. It also contained information about the reality of precious metals pricing.
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| Development: | With further development it became a lesson in smart consumerism, the realization of the actual value/price determination of jewelry, what 14K or 18K gold and sterling silver means in relationship to purity of the precious metal, and how to look up the current market value of silver and gold. It also served as an opportunity for a lesson in the proper use and care of my coveted analytic balances and a quick review of significant figures, etc.
Tying this to a real life application, I related a story about the silver necklace I was wearing that was a gift from my elderly mother who is addicted to QVC and irrationally purchases rip-off jewelry under the psychological pressures of "ONLY 4,389 of these LEFT! Don't miss this once-in-a-lifetime investment opportunity!!!"...etc. I put it to my students to help me figure out a way to convince her that she was being ripped off and to stop spending my inheritance! (Sadly, this IS a TRUE STORY!) I had enough foresight to grab several copies of the business section of the LA Times and bring them to class...and the students dove into the task to determine the actual value of the necklace based on its silver content based on the day's commodity pricing. I have since found that "real time" commodity pricing is now available online.
In addition, the students also calculated the value of gold and silver jewelry they were presently wearing. I caution anyone who might consider doing this as there may be a problem allowing it. I worked with the students in a cooperative yet instructor-led evaluation of the value of the silver content of my own necklace and much to their surprise this $90.00 "INVESTMENT OF A LIFETIME" necklace contained less than $6.00 worth of pure silver.
As the students then focused on determining the pure gold or silver value of their own jewelry, one of my students voiced a concern that perhaps he had made an error in his calculation as the answer was obviously irrational but that he had rechecked it and all appeared to be correct. Without hesitation, I slapped it up on the overhead and had the entire class quickly attempt to follow along with his process and reasoning to see if there was indeed an error. Much to my shock, this young man presented the class with a very large 24 KT gold bracelet that his grandparents had bought him for his 16th birthday with an accurately calculated gold value of almost $400. Expressing my fear that he would now be "rolled" in the hallway, consensus among his classmates was that no one would dare bother this 6'5", 275 lb., varsity linebacker. I vowed I would never allow that again! |
| Closing: | The students were completely wrapped up in this activity. The discussions that followed this lesson were very rewarding for all, ranging from how pricing is determined, to the value of craftsmanship, to the concepts of supply and demand.
As the students filed out at week's end I was left with an interesting comment from one of my students something to the effect of "I really love this class, but is this chemistry?" This was at the end of the second week of instruction.
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| Ideas for extending the lesson: |
| This lesson and activity led directly into another research discovery project challenging the common belief in the rarity of diamonds, the impact of the DeBeers advertising campaigns on consumers http://www.edata.com.za/DeBeers/diamond.html which was tied to our discussion of the properties of matter and allotropes. I have provided a link below to Nova Online for more resources regarding diamonds; "The Diamond Deception" is a great tie-in to this follow-up project.
Nova Online: http://www.pbs.org/wgbh/nova/diamond
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