Transcript Significant Figure Rule 1

Why are sig figs important?
1. They communicate the
precision of the
measuring tools used
by the chemist.
2. They determine how
precise the answers to
calculations (using the
measurements) can
be.
Significant Figure Rule 1
All non zero numbers are always significant.
12345
6789
Significant Figure Rule 2
Zeros between non-zero numbers are
always significant. (Sandwich zeros)
101
Significant Figure Rule 3
Leading zeros are never significant.
0.000000000009
08
0.1
Significant Figure Rule 4
Trailing zeros are sometimes significant.
900
Zeros at the end
of a whole
number are NOT
900.
If you put a
decimal at the end
the zero ARE
significant. You
are saying I know
it is exactly 900.
9.00
Zeros at the end of
a decimal number
are significant.
DON’T WRITE THEM
IF YOU DON’T KNOW
THEM!!!!!
Circle the numbers that
contain 3 sig figs:
900
807
234
67.1
0.87
28
1020
84
0000000765
0.0000341
900030
721
78
09
Practice!
Determine how many significant
figures each has
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•
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25.2 cm =
35.0 s =
0.0044 kg =
30200 m =
2.5 x 1012 mL =
Sig. Figs in Calculations
Multiplying or dividing – the number of
significant figures in the answer must be
the same as the smallest number of
significant figures for any one of the
numbers in the calculation.
Ex: What is the density of an object with a
mass of 10.00 g and a volume of 3.3 ml?
3.0 g/mL
Calculations
 (400)(206)=
80,000
 (4.236)/(2.10)=
2.02
What about (+) and (-)?
Adding or subtracting – the number of
decimal places(precision) in the answer
must be the same as the smallest
number of decimal places (least precise)
measurements used to make the
calculation.
Ex: 1.013 mm + 12.14 mm + 8.0 mm =
21.2 mm
Whole Numbers Ending in 0?
Best to use Scientific Not.
A whole number ending in zeros (like
2000) only has one sig. fig. But often
people mean for it to have more. To
avoid confusion scientific notation
should be used.
2.0 x 103 two sig. fig
2.00 x 103 three sig. fig
2.000 x 103 four sig. fig
Calculations
 (4x102)(2x103)=
8 x 105
 (4.2x102)/(2.10x10-4)=
2.0 x 106