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14 Chemistry: Matter and Change
Solving Problems: A Chemistry Handbook
SOLVING PROBLEMS:
A CHEMISTRY HANDBOOK
CHAPTER
2
Practice Problems
16. Mount Everest is 8847 m high. How many centimeters high is
the mountain?
17. Your friend is 1.56 m tall. How many millimeters tall is your
friend?
18. A family consumes 2.5 gallons of milk per week. How many
liters of milk do they need to buy for one week?
(Hint: 1 L ϭ 0.908 quart; 1 gallon ϭ 4 quarts.)
19. How many hours are there in one week? How many minutes are
there in one week?
2.3 How reliable are measurements?
When scientists look at measurements, they want to know how accurate as well as how precise the measurements are. Accuracy refers
to how close a measured value is to an accepted value. Precision
refers to how close a series of measurements are to one another.
Precise measurements might not be accurate, and accurate measurements might not be precise. When you make measurements, you
want to aim for both precision and accuracy.
Percent error Quantities measured during an experiment are
called experimental values. The difference between an accepted
value and an experimental value is called an error. The ratio of an
error to an accepted value is called percent error. The equation for
percent error is as follows.
Percent error ϭ
ϫ 100
When you calculate percent error, ignore any plus or minus signs
because only the size of the error counts.
Example Problem 2-8
Calculating Percent Error
Juan calculated the density of aluminum three times.
Trial 1: 2.74 g/cm 3
Trial 2: 2.68 g/cm 3
Trial 3: 2.84 g/cm 3
error
ᎏᎏ
accepted value
▲