Chemistry Reference
In-Depth Information
any sense! We can't have the result of a calculation that is more accurate
than the measurements that the calculation was based on. When doing cal-
culations in science, we must take care not to report answers that claim to be
more accurate than the original measurements that the calculations were
based on. How do we do this? By following specific rules for rounding.
Each measurement is considered to have a certain number of what are
called significant digits or significant figures (sometimes called “sig. digs.” or
“sig. figs.” for short). We determine the number of significant digits that a
number shows according to the following rules:
Rules for Identifying the Number of Significant Digits in a Number
Rules
Examples
1.
Any nonzero (digits from 1 to
9) digits are significant.
1.
The number 942, with 3
nonzero digits, shows 3
significant digits.
2.
Any zeros (regardless of how
many) found between two
significant digits are
significant.
2.
The number 50003, with 2
nonzero digits, and 3 zeros
between significant digits,
shows 5 significant digits.
3.
Any zeros that are found to
the right of both a significant
digit and a decimal place are
significant.
3.
The number 75.00, with 2
nonzero digits, and 2 zeros
that are to the right of both a
significant digit and a
decimal, shows 4 significant
digits.
Now, when you look at a number in chemistry, you should always be
aware of how many significant digits you are looking at. Some texts con-
sider numbers such as “500” to be ambiguous examples, because the zeros
don't fall under any of the rules for significant digits. Other texts, including
this one, will not consider “placeholder” zeros, such as those in the number
500, to be significant. As written, the number 500 only shows 1 significant
digit, the nonzero digit. The zeros are not significant, because they are nei-
ther between two significant digits nor to the right of both a decimal and a
