PSS Poster - GCC links

D
SCIENTIFIC MEASUREMENTS
Poster concept and design by Valerie Nicoulaud
Acknowledgements
I would like to thank Dr. Kimberly Smith for supporting the development
of this poster, letting me use her slides, and kindly reviewing my work.
CHM130 Chapter PSS
Scientific Measurements
Adding and Subtracting Measurements
MEASUREMENTS
quantity estimated using an instrument, number with a unit.
SIGNIFICANT FIGURES: final answer is limited by the number with the fewest decimal places.
ROUNDING UP: If needed, round up your final answer.
EXAMPLES OF QUANTITIES MEASURED
Examples
Correct answer
A- Calculator answer
2 dec. pl.
1 dec. pl.
B- Calculator answer
Correct answer
1 dec. pl.
4 dec. pl.
3.0 mL
.
Keep only 1 dec. p.l
Keep only 1 dec. pl.
.
19.1 g
.
1 dec. pl.
rounded up
Round up
.
EXAMPLE OF MEASUREMENT
0
1
2
3
4
5
cm
0
1
2
3
4
5
cm
Multiplying and Dividing Measurements
2.4 cm
SIGNIFICANT FIGURES: final answer is limited by the number with the least number of significant figures.
2.46 cm
ROUNDING UP: If needed, round up your final answer.
All measurements have some uncertainty involved since
instruments can never give exact measurements!
SCIENTIFIC NOTATION: If needed, use the scientific notation to express the answer with the right number of significant figures.
Significant digits (also called Significant Figures or “Sig figs”):
All known digits in a measurement plus 1st uncertain or estimated
digit.

Examples
Correct answer
C- Calculator answer
Determining Significant Figures
4 sig figs
2 sig figs
• First eliminate the non-significant digits
WHOLE NUMBERS
Keep only 2 sig figs
2 3 0 0 5 1 0 0 Trailing zeroes are not significant
xx
.
Round up
.
33
.
Only 1 sig fig! We want to express
this number with 2 sig figs.
.
1.0 x 101 cm3
.
2 sig figs
Use the scientific
notation
.
.
Scientific Notation
Leading zeroes are not significant
ONE DIGIT FOLLOWED BY A DECIMAL POINT: this is a number between 1 and 9.
• Then count the remaining (significant) digits
23005100
xx
0. 0 0 2 3 0 0 5 1 0 0
x. x x
xx
Correct answer
2 sig figs
3 sig figs
2 sig figs
rounded up
Pay attention
to the unit
DECIMAL NUMBERS
0. 0 0 2 3 0 0 5 1 0 0
x. x x
x
x
cm2
D- Calculator answer
EXPONENTIAL TERM THAT IS 10 RAISED TO A POWER: For big #’s > 1 positive exponent, for small #’s < 1 negative exponent.
6 sig figs
Examples
8 sig figs
Rounding Off Non-significant Digits
1. < 5, don’t round up
2. ≥ 5, round up
3. Don't change the magnitude of the number
use placeholder zeroes
Examples
Round these numbers off to 3 significant figures:
100.03 = 1.0003 x 102
0.000340 = 3.40 x 10-4
Exact Numbers
• either DEFINE NUMBER: e.g., one meter is defined as 100 centimeters.
• or
RESULT OF A COUNT: e.g.
3 apples.
Links
Why are Significant Figures Important?
Converting Units using Multiple Conversion Factors
Scientific Notation and Significant Figures
Unit Conversion & Significant Figures: Crash Course Chemistry #2
Apple retrieved from http://www.publicdomainpictures.net/view-image.php?image=37301&picture=red-apple-clipart&large=1
They have no uncertainty.
They do not affect the number of significant figures in calculations.
Example
 100

cm  
5.35 m  
  535 cm
  1m  
Keep 3 sig figs
Additional information
Accuracy how close the measurement is from a correct value
Precision consistency of repeated measurement
.
link: Accuracy and precision

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