BackSignificant Figures and Precision in Measurements
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Significant Figures and Precision in Measurements
Understanding Significant Figures
Significant figures are the digits in a measurement that carry meaning contributing to its precision. The more significant figures a measurement has, the more precise it is considered to be.
Definition: Significant figures include all the certain digits in a measurement plus one uncertain or estimated digit.
Example: A reading of 25.00 mL is more precise than just 25 mL because it includes more significant figures.
Recording Measurements
When recording a measurement, always include all the known numbers plus one additional digit, which is estimated. This estimated digit is based on the smallest division of the measuring instrument.
Decimal Place: The last digit recorded is always an estimate, representing the uncertainty in the measurement.
Eyeball Test: Estimate one digit beyond the smallest marked unit on the measuring device.
Example: Determining Significant Figures
Suppose you are asked to determine the number of significant figures involved in measuring the length of a square using a ruler marked in centimeters and millimeters.
Measured Value: 3.20 cm
Significant Figures: This value has three significant figures (3, 2, and the estimated 0).
Explanation: The first two digits (3 and 2) are certain, and the last digit (0) is estimated.
Practice: Reading Measurements
When reading the length of an object, such as a pencil, always record the value with the correct number of significant figures.
Example: If the pencil measures 8.00 cm, this value has three significant figures.
Practice: Reading Liquid Volumes
To determine the correct reading for the liquid in a burette or graduated cylinder, estimate one digit beyond the smallest graduation.
Example: If the meniscus is between 6.7 mL and 6.8 mL, you might record the value as 6.78 mL (three significant figures).
Key Points Summary
More significant figures = greater measurement precision.
Always estimate one digit beyond the smallest marked unit.
Significant figures reflect both the accuracy of the instrument and the care of the observer.
