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Unformatted text preview: a regular solid the volume is:
V = length × width × height
We note that the dimensions are all in cm except the 62 mm. Convert this to centimeters.
62 mm × 1 cm
= 6.2 cm
10 mm The volume is
V = 20.5 cm × 9.7 cm × 6.2 cm = 1233 cm3
V = 1.2 × 10 3 cm3 (two significant figures)
Substituting into the equation for mass
m=d×V
11.4 g
m=
× 1 .2 × 10 3 cm3 = 1.4 × 10 3 g
cm3
The last step in solving the problem is checking the answer. Is it reasonable in size and units. One way to
check an answer is to estimate it in your head with rounded numbers. If the density of lead is about 10 and the
volume was 1200 cm 3 , then the answer should be close to 12,000 g, which it is. Also the units of grams are
correct for mass.
•Comment
When solving problems, based on an equation such as this example was, notice that we followed three steps.
1. Rearrange the equation so that the unknown quantity is by itself on one side.
2. Substitute in known quantities including their units.
3. Calculate the answer including its units.
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EXAMPLE 1.14 A Conversion of Volume Units
How many cubic centimeters are equal to 5 m3 ?
•Method of Solution
The desired unit is cm3 .
? cm3 = 5 m3
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This note was uploaded on 09/15/2009 for the course CHEM 102 taught by Professor Bastos during the Spring '08 term at Adelphi.
 Spring '08
 BASTOS
 pH

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