Thursday, September 16

We started off today’s class by going over last nights blog, done by Alex P. Mr. H then continued on to talk about the expectations for Lab MM5, which was to make sure you wrote a couple of paragraphs describing the chemical reactions of the substances you tested. Mr. H took a few minutes to review the five pieces of evidence that characterize chemical change, which were evolution of gas, solid being formed, production of heat or light, change in color, and temperature change. Next Mr. H started our lesson on density. We went over the Chapter 1.3 reading sheet (page 21) and took some notes on density in the margin.

NOTES FROM CLASS DISCUSSION:

The big idea was that every substance has a unique set of identifying properties; these properties distinguish the substance from other substances. For example: Water is a colorless substance that boils at 100 degrees C, freezes at 0 degrees C, has a density of 1.0 g/mL and a heat capacity of 4.18 J/gC.

· Intensive vs. Extensive Properties

o Intensive- identifying does not depend on amount

o Extensive- (usually volume and mass) depends on amount

· Chemical Properties: describes how a substance reacts (or not) with other substances

· Physical Properties: describes a substance apart from how it reacts

· Three common physical properties: density, solubility, and color

· DENSITY

o A measure of how tightly that mass is packed into a given volume of space

o Density= mass/volume

o Units: g/cm^3, g/mL, kg/L, kg/mL

After Mr. H explained density, he went through the answers to the 1.3 reading sheet:

1. .A

2. .A. PP, B. CP, C. PP, D. CP

3. .FALSE- The density of a material is specific to that material and not dependent on the amount.

4. .A

5. .D

6. B

7. .C

8. .A

Mr. H noticed that many people didn’t understand how to do number 4, which involves knowledge of significant digits. If you still don’t understand or would like to practice it more then you should go to this website or see packet page 6: http://www.physics.uoguelph.ca/tutorials/sig_fig/SIG_dig.htm

After we did our review and notes, Mr. H explained Lab MM7. The lab was called Dense Cents Lab and the question was “What is the density value of pre- and post-1982 pennies? How do their density values compare? How can the difference be explained?” The purpose was to use a plot of mass vs. volume to determine and compare the density value of pre- and post-1982 pennies and to explain the difference between their densities. First each group separated the pennies into two groups, one with pre-82 and one with post-82 pennies.

Then we measured out 50 mL of water into a graduated cylinder. This was going to be used to find the volume of the pennies, using displacement. Displacement is where you add the objects to the water and difference between the original volume and the new volume is the volume of the object. We massed the pennies in groups of 5 up to 30. After massing each group of 5 we then put them in the graduated cylinder to find the volume. We then divided the volume from the mass of each set to find the density.

Based on the data that we collected, the pre-82 pennies seem to have a higher density. The pre-82 pennies had a total density of 50.095 and the post-82 pennies had a density of 53.545.