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16
Chapter One
Chemical
Foundations
Note that for multiplication
and division,
significant
figures are counted.
For addition
and subtraction,
the decimal
places
are counted.
In most calculations
you will need to round numbers
to obtain the correct number
of
significant
figures. The following
rules should be applied
when rounding.
Rules for
Rounding
Rule 2 is consistent with the operation of
electronic calculators.
1. In a series
of calculations,
carry the extra
digits
through
to the final
result,
then
round.
2.
If the digit
to be removed
a.
is less than
5, the preceding
digit
stays the same.
For example,
1.33 rounds
to 1.3.
b. is equal to or greater
than
5, the preceding
digit
is increased
by 1. For
example,
1.36 rounds
to 1.4.
Although
rounding
is generally
straightforward,
one point requires
special emphasis.
As an illustration,
suppose
that the number
4.348 needs to be rounded
to two significant
figures. In doing this, we look
only
at the
first
number
to the right of the 3:
4.348
i
Look at this number
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This note was uploaded on 12/13/2010 for the course CHEM 2301 taught by Professor Bill during the Spring '10 term at South Texas College.
 Spring '10
 bill
 Organic chemistry

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