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1
Precision and Accuracy 
Think of a Dart Board!!!
Precision is the closeness
of a set of values
obtained from
identical measurements
(are your darts clustered??)
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Accuracy is the closeness
of a single measurement to
the true value (the bullseye!)
Precision vs. Accuracy
Draw the Dart Board Showing Each of These:
good precision & good accuracy
poor accuracy but good precision
good accuracy but poor precision
Precision & Accuracy
Compared
3
The DREADED “Significant Figures”
Those digits in a measured number that
include all certain digits and final one have
some uncertainty
Rules for assigning significance to a digit:
1. Digits other than zero are always significant.
2. Rules about zeros:
Final zeros after a decimal point
are always significant.
Zeros between two other significant
digits are always significant.
Zeros used only to space the decimal
are never significant.
Determine the number of significant
digits in each of these:
6.751 g
0.157 kg
28.0 ml
2500 m
0.070 g
30.07 g
0.0067 cm
6.02 x 10
23
atoms
Scientific notation!!!
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A)Between 0 and 2 in
b)Between 1 and 2 in
C)Between 1.5 and 1.6 in
D)Between 1.54 and 1.56 in
E)Between 1.546 and 1.547 in
Which of the following best
describes the length of the
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This note was uploaded on 01/12/2012 for the course CHEM 103 taught by Professor Jeffashley during the Fall '10 term at Philadelphia.
 Fall '10
 JeffAshley

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