DENSITY AND GRAPHING: September 30, 2010

Density

The density of an object is it's mass divided by it's volume

and is usually expressed in

More on Density

Graphing

All graphs must contain 5 important things:

1. Labelled axis
2. Appropriate scale (the data should take up at least 2/3 of the graph)
3. Title
4. Data points
5. Line of best fit

3 things can be done when working with graphs:

1. Read the graph (before you start taking information from it, read the whole thing!)
2. Find the slope (rise over run)
rise
run
3. Find the area under the graph (you will, in some cases, need to split the space under the graph into manageable sections so you can get the area of each and add it together)

How to Find Slope

The slope of a line is rise over run.
The rise on the graph would be the Y axis, while the run would be the X axis.
To find the slope, plot the data points and find the line of best fit. (You can try placing your data points in such a way that it corrisponds to the scale so that the line of best fit starts from the bottom corner.)
Once you have your line of best fit, choose a point on the line and find out the rise # and the run #.
Divide the rise by the run, and you have your slope!

Example:

...and that's all for today!

Post by Adrienne Ross

DIMENSIONAL ANALYSIS: September 28, 2010

Want to know how to Convert Units? This blog post will help you :)

Here is a video from youtube that will help you with Dimensional Analysis. Skip to 2:40 when he gets to the good stuff.
 Just like converting between currencies, in chemistry it is usually necessary to convert between units.

This process is called Dimensional Analysis and is showed in the video above!

1. FIND A UNIT EQUALITY
2. FIND THE CONVERSION FACTORS
3. APPLY CONVERSION FACTOR
4. CANCEL UNITS!

Post by Ren Flores

SCIENTIFIC NOTATION AND SIGNIFCANT DIGITS: September 23, 2010

Today we learned that Accuracy and Precision is very important in Science!

Calculators are not smart enough to decide what is precise and what isnt so dont follow them!

• Scientists have established a set of rules for rounding off extra digits; You MUST follow them if you want to exceed!

Note: CONSTANTS (pie, etc) have infinite Significant Digits! Pretty cool huh?

We also learned about Scientific Notations:

Post by Ren Flores

SI SYSTEM AND PERCENT ERROR: September 21, 2010

Today in class, we learned about the different units of measurements, such as common Metric Prefixes used in Chemistry.

We also learned about Experimental Accuracy. Not all experiements will result with very accurate results so we use a special symbol to show uncertainty of a measurement. A plus-or-minus symbol, ± is used.

*the menuscus is only measured on the top with certain liquids that curve that way
In the example above, the meniscus falls between 31-32. Since it is not on 31 but is less than 32 we could estimate the meniscus is about... 31.7mL. To show our uncertainty, we add ± to our measurement as follows -> 31.7 ± 0.1milliliters. This reads: "Thirty- one and seven tenths plus-or-minus one tenth milliliters."

Last but not least...
We learned about expressing ERROR

1. Error is a fundemental part of Science and there are usually 3 reasons for error:

• Physical Errors in the measuring device
• "Sloppy" measuring (i.e Being lazy and not taking proper measurements)
• Changing abient conditions

TWO DIFFERENT POSSIBILITIES:
-Absolute Error & Percentage error

Absolute Error

•  Absolute Error= Measured- Accepted
• Its measured value minus accepted value will give you absolute error.

Percent Error

• Most common
• Percent Error= Absolute/Accepted Value
• %Error= [Measured-Accepted÷Accepted] x 100

ie. You measure the weight of an orange to be 15 N. The actual weight is 17.5 N. What is the percent error?

15(measured)-17.5(Accepted)     than times by x100 = 14%
17.5(Accepted)

Post by Ren Flores

CLASSIFICATION OF MATTER: September 17, 2010

We learned about Classifying matter as either a Homogeneous substance or a Heterogeneous substance. Understanding matter begins with how we name it!

Post by Ren Flores

WELCOME TO OUR BLOG: September 11, 2010

Group Members: Adrienne Ross, Russell Flores, Ivy Gloria

Block G/ Room 403

Instructor: Mr.Doktor