Chemistry / Unit 1 Chem 0129 worked example, 60 to 90 seconds
Counting Significant Figures with Zeros
The idea
Counting significant figures means treating all nonzero digits as significant, then classifying each zero as leading, captive, or trailing to decide whether it counts.
In practice
In 0.02030, the leading zeros only locate the decimal point and are not significant, the captive zero between the 2 and 3 is significant, and the trailing zero is significant because it appears after the decimal point — giving four significant figures total (2, 0, 3, 0). In 1,300, without a decimal point, the trailing zeros are ambiguous and are conventionally treated as not significant unless written as 1.300 × 10³.
Where people slip
A trailing zero to the left of a decimal point, as in 1,300, is the case students get wrong most often — writing the number in scientific notation is the only way to remove the ambiguity entirely.
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