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chloe ko.
christina chow.
mr. doktor's chemistry class
block g

home. mrdoktor.

Density and Graphing

Density:
-the desity of an object is it's mass divided by it's volume.
D = m/v

Example:
Determine the density of a boulder that ahs a mass of 188kg and a volume of 52L.
D= 188kg / 94L
D= 2 kg/L

Graphing:

All graphs must contain 5 important things:
1. Labelled axis
2. Appropiate Scale
3. Title
4. Data points
5. Line of best fit

3 things can be done when working with graphs:
1) Read the graph
2) Find the slope
3) Find the area under the graph.

Example:
The data below represents the how long 6 students take to get school by walking in a day.

Students             Time [mins]    
  A                        5 mins
   B                        25 mins
   C                        60 mins
   D                        60 mins
   E                         40 mins
   F                         20 mins
  G                        0mins

          Slope: m = rise/slop
   1.  m= 12/3 =2 mins/ student
   2.  m= 0/0 =0 min/student
   3. m= 12/4= 3 mins/student



















Area: 1/2 (b)(h)
J= 1/2 (3)(12)
 = 18
K= lw = (2)(6)
  = 12
L= 1/2 (4)(12)
  =24

Area= 54mins/students

~Christina Chow :]

         


~christina :]


SIGNIFICANT DIGITS

• Today, we learned that accuracy and precision is VERY important in science so its important to communicatethis accuracy carefully.
• REMEMBER that calculators are not smart enough to decide that is precise and what is not, so you have to be the judge of that.
• Scientists have establish rules for rounding off extra digits so you MUST follow them!
• Non-zero digits are always significant
• If zero is a place keeper, it is generally NOT significant 

for example:
0.00027

• Any numbers to the left of a decimal point are significant.

examples:
143.0052
88.2010

• zeros after another number are significant.

example:
8.127       --------------4 significant digits
92.32135 --------------7 significant digits
0.0000150 -------------3 significant digits

• When adding or subtracting round to the least precise number.

examples:
9.1121-8.04 = 1.0721 ------------>1.07
2.4+83.2336=85.6336------------>86

• When you multiply or divide, round the number with the fewest significant digits.

examples:
4.11 x 0.0039 = 0.016029 ---------------------->0.0160
85.234 / 9.115608 = 9.350336258-------------->9.3503

• Constants (π, G, ect ) on your data sheet have infinite significant digits

SCIENTIFIC NOTATION

• Used if we need to write the number 3000 with only 2 SDs

example:
3.0 x 10^3 

• Used if we want to write the number 22 billion 5 hundred million without taking up an entire line 

example:
22,500,000,000      = 2.25 x 10 ^10

• Shows really big or really small numbers easily 

• Makes use of power of 10 

examples:
10^7 = 10,000,000
10^-7 =0.0000007


CALCULATORS

• Your calculator has funtions that you can use to do this easily 

• DON'T use the "^" sign on your calculator. It does not recognize the order of operations in all cases.

SI System & Percent Error


Today, we learned about the SI System and Percent Error. Mr. Doktor showed us a video on youtube about the powers of ten.


http://www.youtube.com/watch?v=aPm3QVKlBJg

PREFIXES USED WITH SI UNITS AND SI PREFIXES

We learned that we can put a prefix in front of the unit and change the power of it. The SI system uses many prefixes to represent very large or very small numbers.

TERA -----(T)~~~~10^12
HECTO---(h)~~~~10^2
GIGA------(G)~~~10^9
DECA-----(da)~~10^1
MEGA----(M)~~~10^6
KILO-----(k)~~~~10^3
DECI -----(d)~~~~10^-1
CENTI---(c)~~~~10^-2
MILLI------(m)~~~10^-3
MICRO-----(u)~~10^-6
NANO----(n)~~~10^-9
PICO-----(p)~~~~10^-12FEMTO-----(fm)~~~~10^-15


* REMEMBER!!! DON'T use scientific notation and prefixes together! It becomes VERY confusing. 


We also learned about Experimental Accuracy, that not all measurements are accurate. Any measurement are usually half of the smallest division of the measuring device. We use a plus-or-minus symbol, ± instead. A graduated cylinder has units of 1.0mL. The accuracy of the cylinder is ±0.5mL. As Mr. Doktor showed us in class, when he added water in the graduated cylinder, the water formed a curved top called a meniscus. The volume is taken at the bottom of a meniscus. 


Lastly, we were taught about expression error, absolute error and percent error.


Error is a fundemental part of Science which there are usually 3 reasons for error.
1) Physical Errors in the measuring device
2) "Sloppy" measuring [like not measure correctly]
3) Changing abient conditions
There are two different possibilites, absolute error and percentage error.


ABSOLUTE ERROR
~measured value minus accepted value
Absolute Error= Measured- Accepted


PERCENTAGE ERROR
Its the most common error.
~Percent Error= Absolute/Accepted Value
%Error= (Measured-Accepted) x 100
                     Accepted
AN EXAMPLE MR.DOKTOR gave us was:
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]) x100 = 14%
17.5[accepted]