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Solving Problems: A Chemistry Handbook
Chemistry: Matter and Change
15
SOLVING PROBLEMS:
A CHEMISTRY HANDBOOK
CHAPTER
2
Aluminum has a density of 2.70 g/cm 3 . Calculate the percent error
for each trial.
First, calculate the error for each trial by subtracting Juan’s measurement from the accepted value (2.70 g/cm 3 ).
Trial 1: error ϭ 2.70 g/cm 3 Ϫ 2.74 g/cm 3 ϭ Ϫ0.04 g/cm 3
Trial 2: error ϭ 2.70 g/cm 3 Ϫ 2.68 g/cm 3 ϭ 0.02 g/cm 3
Trial 3: error ϭ 2.70 g/cm 3 Ϫ 2.84 g/cm 3 ϭ Ϫ0.14 g/cm 3
Then, substitute each error and the accepted value into the percent
error equation. Ignore the plus and minus signs.
Trial 1: percent error ϭ
ϫ100 ϭ 1.48%
Trial 2: percent error ϭ
ϫ100 ϭ 0.741%
Trial 3: percent error ϭ
ϫ100 ϭ 5.19%
Practice Problems
20. Suppose you calculate your semester grade in chemistry as
90.1, but you receive a grade of 89.4. What is your percent
error?
21. On a bathroom scale, a person always weighs 2.5 pounds less
than on the scale at the doctor’s office. What is the percent error
of the bathroom scale if the person’s actual weight is 125
pounds?
22. A length of wood has a labeled length value of 2.50 meters. You
measure its length three times. Each time you get the same
value: 2.35 meters.
a. What is the percent error of your measurements?
b. Are your measurements precise? Are they accurate?
0.14 g/cm 3
ᎏᎏ
2.70 g/cm 3
0.02 g/cm 3
ᎏᎏ
2.70 g/cm 3
0.04 g/cm 3
ᎏᎏ
2.70 g/cm 3