How To Take Measurements:
Here are some rules that you should follow when taking measurements on various equipment:
 For digital equipment (the type that shows you the numbers on a little screen), just write down whatever it says.
For example, if the numbers say “1.20 grams”, you should record “1.20 grams” as your data.
 For analog equipment (it’s got some sort of scale with lines on it that you have to figure out for yourself), write
down the answer you directly get from the equipment and add one digit that you estimate.
Significant Figures:
Significant figures (often referred to as sig figs) are an important concept when working with measurements. The
significant figures in a measurement include all the digits that are known for certain, plus a last digit that is estimated.
Measurements must always be reported to the correct number of figures because calculated answers often depend on the
number of significant figures in the values used in the calculation.
RULES FOR DETERMINING SIGNIFICANT FIGURES
Rule #1: Nonzero digits always count as significant figures:
Examples:
438 g
26.42 m
1.7 cm
0.653 L
_____ sig fig
_____ sig fig
_____ sig fig
_____ sig fig
Rule #2: Captive zeros always count as significant figures:
Examples:
506 dm
1005 mL
900.43 kg
20.006 cm
_____ sig fig
_____ sig fig
_____ sig fig
_____ sig fig
Rule #3: Leading zeros do not count as significant figures:
Examples:
0.8 g
0.06 g
0.0047 L
_____ sig fig
_____ sig fig
_____ sig fig
Rule #4: Trailing zeros are significant only if the number contains a decimal point:
Examples:
60 g
4830 km
8.0 dm
1.60 sec
35.000 L
0.002450 kg
_____ sig fig
_____ sig fig
_____ sig fig
_____ sig fig
_____ sig fig
_____ sig fig
RULES FOR ROUNDING OFF NUMBERS
If the digit immediately to the right of the last significant figure you want to retain is:
1. Less than 5 ------ the last significant digit should stay the same.
Example:
Round 17.32 m to 3 significant figures.
Since the 2 is less than 5, you should round to __________ m
2. 5 or greater --------- the last significant figure should increase by 1.
Example:
Round 42.68 g to 3 significant figures.
Since 8 is greater than 5, you should round to __________ g
CALCULATIONS WITH MEASUREMENTS
Rule #1: Whenever you add or subtract measurements, your answer should have as many DECIMAL PLACES
as the measurement with the LEAST number of DECIMAL PLACES. Write an example.
EXAMPLE:
Rule#2: Whenever you multiply or divide measurements, your answer should have as many SIGNIFICANT
FIGURES as the measurement with the LEAST number of SIGNIFICANT FIGURES. Write an example.
EXAMPLE:
Advanced Honors/Honors Chemistry: Sig Figs & Scientific Notation
1.
Record the volume of liquid in the graduated cylinder to the correct number of digits.
2.
Determine the number of significant figures in each of the following:
(a) 245.3 mm
(e) 0.007 kg
(b) 605.03 g
(f) 350.0 K
(c) 300 dm
(g) 450 m
(d) 0.0080 L
(h) 10.0040 mL
3.
Round each of the following measurements to the indicated number of significant
figures:
(a) 35.27cm to 3 significant figures
(b) 0.414 kL to 2 significant figures
(c) 1.35 m to 2 significant figures
(d) 87.257 g to 3 significant figures
(e) 6250 dL to 2 significant figures
4. Perform the following calculations. Express your answer to the correct number of digits .
(a) 81.32 I 6.50 =
(d) 87.3 - l.655 =
(b) 2.099 + 0.05681 =
(e) 1.34 x 0.075 =
(c) 102 - 1.6 =
(f) (0.3287)(45.2) =
5. Record the volume of water in each of the following beakers to the correct number of digits.
6. Calculate the total volume of water in question 5.