# Learning about Dimensional Analysis and Stoichiometry

#### Summary

In this lesson, students will learn what dimensional analysis is and why it is so important as they are lead through a guided inquiry activity and read an article from Chem Matters entitled The Crash of Flight 143. Students will be lead through a SMART Notebook lesson in which the students arrive at what the rule is for Dimensional Analysis, critically analyze and look at what is wrong in certain examples and solve dimensional analysis problems on the SMARTBoard.

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## Learning Goals

This activity is designed for students to learn what dimensional analysis is, why it is important, and how to apply it to problem solving. Students will develop critical thinking skills by having to try to find patterns and make observations.

## Description and Teaching Materials

This activity is designed to introduce dimensional analysis so that students will have a solid foundation for moving onto stoichiometry. You will want to open up the SMART Notebook file and tell students you are going to start the lesson today with a game. Flash the first slide and have them carefully look at the slide without saying anything to anyone else. Then flash the next slide and have them look again to see if they can see the pattern. Then flash the third slide and have them do the same. You may have them turn to a neighbor and discuss to see if they figured out the pattern for about 30 seconds.
Then you will want to move onto the fourth slide and have some students come up and fix the problem. There is more than one thing that needs fixing, so you can ask student to change one thing, and then have someone else come up and change the next thing. On the fifth slide, have the students look at it and see if they can figure out what the missing piece is and have someone come up and drag it in from the gallery.

The next slide has actual conversion factors on it. Have students come up and drag the appropriate number and unit into the correct spot until you are able to solve the problem. (Note: the numbers are infinite cloned so that when students drag the numbers, they will still remain in their original spot as well) Again, you can have multiple students come up and solve this problem since there are several different steps.
The 7th slide again, allows the students to critically analyze a problem that is already done and you can students come up to make it correct.

After discussing the above slides, there are a couple of slides that review the rules of the game and discuss equalities and labeled rations.

You can use the rest of the slides as practice for the students. I would have them work it in their own notebooks, and then have a few students come up and write the work out on the board.

Provide a worksheet of dimensional analysis for the students, again emphasizing the importance of showing their work appropriately and canceling units when possible.

When you are confident that the students are able to understand how to do dimensional analysis, show the last slide and ask them who needs to do this anyway? Have them read the article the Crash of Flight 143, which is available through Chem Matters and answer the provided questions with the article. (October 1996.)

http://portal.acs.org/portal/acs/corg/content?_nfpb=true&_pageLabel=PP_TRANSITIONMAIN&node_id=1090&use_sec=false&sec_url_var=region1 SMART Notebook File to present material ( 847kB Sep18 08) PDF of Lesson - none interactive in case you don't have SMART Notebook software but want to view the lesson (Acrobat (PDF) 458kB Sep18 08)

## Teaching Notes and Tips

Sometimes students have a hard time remembering to cancel units in the problem. You can pick an arrow from the tool bar and emphasize crossing out the units as you go by drawing a diagonal arrow. You can start this on the domino examples at the beginning of the lesson. It will really help your visual learners see that you need to cross out diagonally. Students also have a hard time plugging in numbers in their calculators when there are multiple numbers in the numerator and denominator. You may want to give them some tips on this, depending upon the level of math your students are at. In the slides, look for the use of the infinite cloner, this will allow you to drag numbers, unit and symbols for manipulation on the lesson.

In the past when I have taught this lesson, it has been more of a lecture. I gave them the notes and I told them how to do dimensional analysis and then we practiced together. In this lesson, I am having them develop the rules of the game and I'm giving them much more visual and kinesthetic practice than I have in the past with the use of the infinite cloner. I also have not addressed the importance of this other than it will be a really valuable tool in science. I'm now trying to pull in some reading material which will help them with reading strategies as well as see how it can impact people in the real world.

## Assessment

I will see how well students understand the concepts as students come up to the board and manipulate things on the board. As they try these problems, I will be walking around checking with students as they work and I will provide them a homework assignment that will also show their understanding. As a follow-up activity at the beginning of class the next day, I will give the students a short quiz to check for understanding.

## Standards

9-12.II.B - chemical reactions/ stoichiometry.