SIGNIFICANT FIGURES
There is some uncertainty in every measured quantity.
Every reported result should reflect the
precision of the measurement.
Significant figures are important in lab because they tell us how
precisely we know a quantity and how well we can reproduce a laboratory measurement.
(The
term “accuracy” is used to refer to how closely a value measured in the laboratory is to the
“true” value.)
Consider two densities, 0.8 g/mL and 0.826 g/mL.
The 0.826 g/mL number is
more precise.
The last digit on the right a
lways indicates the “uncertain” or “doubtful” digit
because we do not know what the digit directly to
its
right is.
Here are the rules for determining the number of significant figures:
a)
Nonzero digits are
always
significant.
b)
Zeroes may or may not be significant, depending on where they are in the number.
(1)
zeroes between other nonzero digits are always significant
(2)
zeroes to the left of the first nonzero digit are never significant
(3)
zeroes to the right of the last nonzero digit
to the right of the decimal point
are
significant
(4)
zeroes to the right of the last nonzero digit, not in a decimal, may or may not be
significant; use exponential notation for a precise expression of sig. figs.
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 Fall '08
 PREZHDO
 Chemistry, Decimal

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