**the Metric system**,

**significant figures**and reviewed

**scientific notation**. With this foundation, your students are ready to learn a very important skill, that of

**dimensional analysis**(also known as

**the factor-label method**).

It is a skill the also gets students used to reading measurement units and recognizing the importance of the units to calculate the final answer of any situation -- this is important in the study of Chemistry, and Physics.

I have viewed some videos showing this method, but I found them to be overly complicated. I’m going to discuss the approach here and show a few examples.

**Dimensional analysis**(or the factor-label method) is a way to convert measurements between systems, along with several unit changes.

A chart for reference is:

**51.8 ounces x __________________**

where the line the beginning of the conversion factor.

Then enter the units first (the numbers will be entered later):

51.8 ounce x __________

__gram ____

ounce

The values can then be entered, and the set-up can become on big fraction:

__51.8 ounce x_______

__1______

__gram ____

0.035 ounce

And the “ounce” unit cancels and “gram” remains:

__51.8 ounce x_______

___ 1_____

__gram ____ = 1480 grams or 1.48 x 10 3 grams

0.035 ounce

The conversion values are not considered to be limiting, so the answer would have the same number of significant figures as the beginning value (which has 3 sig figs).

The chart above also contains the equivalence 1 ounce = 28.349 grams,

so the conversion could be set up:

__51.8 ounce x 28.349 grams__= 1470 or 1.47 x 10 3 grams

1 ounce

Note that the last significant figure is different by one number, and that is the value that is an estimate.

A few worksheets for the introduction of this topic are:

__http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&sqi=2&ved=0CCMQFjAB&url=http%3A%2F%2Fwww.atlanta.k12.ga.us%2Fsite%2Fhandlers%2Ffiledownload.ashx%3Fmoduleinstanceid%3D9044%26dataid%3D44848%26FileName%3D6%2520Hwk%2520dimensional_analysis_worksheet.pdf&ei=ALoFVLuwCsaxggTpmICYCw&usg=AFQjCNHeRmLD1XWUkDLeO2f-FBkUW152aw&bvm=bv.74115972,d.aWw__

__http://teacherweb.com/LA/MandevilleHighSchool/Chausse/013.DimensionalAnalysisReview2.pdf__

This is several pages, but has a handy description of the technique as well as problems:

__http://www.flanaganhighschool.com/files/_gDDgM_/5c3bcc427e96a23b3745a49013852ec4/Dimensional_Anal_Worksheet_001.pdf__

This worksheet contains some more difficult examples:

__http://www.acschools.org/cms/lib07/PA01916405/Centricity/Domain/362/Dimensional%20Analysis%20Worksheet.pdf__

One question that is more complicated follows:

- The painter Raphaeleoeo is said to have worked at the rate of 1.0 ft2/hour. Using the factor-label method, calculate his rate expressed in cm2/century? (10) (Assume a standard year of 365 days; 100 years = 1 century)

__1.0 ft 2 x 12 in x 12 in x 1 cm x 1 cm__

Hour 1 ft 1 ft 0.3937 in 0.3937 in

__x 24 hours x 365 days x 100 year__=

__8.1 x 10 8 cm 2__

__1 day 1 years 1 century century__

Another possibility for dimensional analysis practice is using conversion of currency to various denominations. The following link contains several worksheets:

__http://www.wasatch.edu/cms/lib/UT01000315/Centricity/Domain/588/Currency%20Conversion%20Worksheets.pdf__

**You can purchase my lab book "Chemistry on a Budget" through**

**amazon.com**

**and**

**l**

**ulu.com**

**for only $20!**The book contains 13 labs that require consumable materials you can purchase at local stores.

__http://www.amazon.com/Chemistry-Budget-Marjorie-R-Heesemann/dp/0578129159/ref=sr_1_1?s=books&ie=UTF8&qid=1389410170&sr=1-1&keywords=chemistry+on+a+budget__

**Each lab is presented with two possible report formats**-- both labs use the same procedure but each has a different conclusion -- one with 10 questions to be answered as a conclusion, the other with a full laboratory report required. This gives the teacher the option of what type of report is desired. Each version is

*designed to be just two pages*. This way the teacher can photocopy just one 2-sided page per student (saves paper).

I hope your start of the school year is going well!

**I am changing the day of my new blog posts to Friday – this is to give you the entire weekend to read the new post.**My next post will be this Friday, September 5th.

BTW, I'd love to hear from you with your questions or suggestions for blog topics.

Enjoy the rest of the week!