**Density**.

Unit Objectives:

1. Define

**Density**and explain how it is calculated.

2. Calculate one variable in Density = mass / volume (D = m/v) when given the other two variables.

A neat example of density changes is a lava lamp -- it's not very expensive and it's a dynamic example of the concept. (I used to have one in my classroom, but... it got stolen-- so store your stuff away!)

Here's a video discussing the concept and showing a few problems. (there is a small inconsistency in Problem #1)

For your information, from D = m / v:

v x D = (m / v) x v --> v x D = m

(v x D) / D = m / D --> V = m / D

I point out to my students that all three formulas are in "D = m/v" , it just needs to be rearranged algebraically.

Here is another video showing Density examples using a Factor-Label approach:

Here are some worksheets for your class:

http://www.chsd.us/~tthompson/assignments/Physical%20Science/density%20formula%20wkst.pdf

http://www.lz95.org/assets/1/6/Denisty_WS.pdf

http://wa.westfordk12.us/pages/westfordwa_teachers/brown%20WEB/Docs/Unit%201%20CH%20Density%20Practice%20Worksheet.pdf

The following worksheet might print out a little faded, but I like the variety of questions:

http://www.bloomhs.org/ourpages/auto/2008/9/25/1222364253225/pg%2019%20and%2020.pdf

During this beginning month of Chemistry class, many Density labs can be performed safely -- this gives time to learn about chemical and fire safety and get lab safety contracts signed.

Here is a quick review of reading a graduated cylinder:

Once objects are collected for these labs, you could use them the next year. Check in your Science Department to see if there's already a collection of objects used for Density labs.

The 2nd method in the lab is for irregularly-shaped objects -- the method of Water Displacement is to be demonstrated by the teacher. This video provides a reminder of this technique -- it's not concerned about Significant Figures -- you can measure to one decimal place with the graduate cylinder used:

A graph of the data collected is required in the data analysis. If you want to graph by hand, here is a link to blank graph papers for your use:

http://incompetech.com/graphpaper/square.html

I recommend drawing the points and line for one liquid before moving to the next liquid. Use a symbol around the points to differentiate the lines for the three substances (for example, circle, square, triangle). Include a Key on the graph to identify the line symbols.

Here's an online graphing program:

http://graphsketch.com/

And a sample version of Graphical Analysis is available:

http://www.softpedia.com/get/Multimedia/Graphic/Graphic-Others/Graphical-Analysis.shtml

Check in your Science and Math Departments to see if your school owns a graphing program.

One more simple lab dealing with Density and the importance of Significant Figures is "Thickness of Aluminum Foil" . It's interesting to collect the class results, maybe on the board. With those values, you can discuss the consistency of the results.

My lab book "Chemistry on a Budget" is available for $20 at amazon.com or $23 at lulu.com:

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

http://www.lulu.com/shop/marjorie-r-heesemann/chemistry-on-a-budget/paperback/product-21217600.html

The book contains 13 labs that require consumable materials you can purchase at local stores.

**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 school year is going well! Write me to let me know about your triumphs, challenges and questions!

Have a great weekend!