SEPTEMBER 6, 2012

C H E M I ST R Y 2

0

A JOKE…

AGENDA• Taylor Wilson• Significant Figures• SI Units• Worksheet

• This is Taylor Wilson.

• What do you think he is well known for?

TAYLOR WILSON

TAYLOR WILSON• Link to Video

TAYLOR WILSON

“The Boy Who Played With Fusion”

ACCURACY & PRECISION• Accuracy tells us how close we were to a desired result.• Precision tells us how close our results were to each other.

How reproducable our results are.• It is possible to have a measurement system that is

accurate, but not precise. Precise but not accurate. Both or neither.

SCIENTIFIC NOTATION• A way of writing numbers that are too

big or too small to be conveniently written in standard form

• Commonly used in calculators and often used by scientists, engineers, and mathematicians.

SCIENTIFIC NOTATIONHow to write in scientific notation:• Take your number•Ex: 34500

• Convert it to a decimal.•Ex: 3.45

• Write x10b after it, where b is the number of spaces the decimal has moved.•Ex: 3.45 x 104 = 34500

SCIENTIFIC NOTATION

SCIENTIFIC NOTATIONConvert the following to scientific

notation:

• 545000• 23400000• 0.0012• .00004901

SIGNIFICANT FIGURESWhy are significant figures

important?• Because they tell us how accurate

our results are.

SIGNIFICANT FIGURESHow do we determine the number of

significant figures?• Four simple Rules!

SIGNIFICANT FIGURESRule 1: All non-zero digits, are

ALWAYS significant.

• EX: 345 3 significant figures (sig figs)

SIGNIFICANT FIGURESRule 2: All zeroes between non-

zero digits, are ALWAYS significant.

• EX: 3091 4 sig figs

SIGNIFICANT FIGURESRule 3: Zeroes placed before other

significant digits are NOT significant.

• EX: 0.32 2 sig figs• EX: 04449 4 sig figs

SIGNIFICANT FIGURESRule 4: Zeroes placed after other

significant figures are only significant if they are behind(after) a decimal.

• EX: 117000 3 sig figs• EX: 65.0 3 sig figs

MULTIPLYING/DIVIDING SIGNIFICANT FIGURESWhen multiplying/dividing, the number of sig figs in the answer should be the same as the number that has the fewest number of sig figs being multiplied/divided.

• EX: 2480 x 12.00 = 29,760 = 2.98 x 104

3 4 3• Note that the answer gets rounded to the

nearest place.• It is usually easier to write your answers in

scientific notation.

ADDING/SUBTRACTING SIGNIFICANT FIGURESWhen adding/subtracting, your answer should have the same number of decimal places as the number with the least amount of decimal places being added or subtracted.

• EX: 45.002 + 13.6 = 58.6• Once again the answer is rounded to show

the correct number of significant digits.

ASSIGNMENT• Work on the booklet that is being

handed out.• It is due Wednesday (Sept. 12)