Untitled - Kelly Walsh High School

10 CHEMISTRY FOR THE UTTERLY CONFUSED
Careful!
Clearly any of these procedures, and many more, will work. In this case, we will
use the first:
Density (Mass)
(Volume)
We also need to perform a volume conversion. As with the mass conversion,
there are many different correct volume conversions. In this case, the conversion
will relate, in some way, to the length unit of feet. Thus, we might use 12 in
1 ft. If we incorporate this, we get:
This will leave us with ft 2 ⋅ in. This is not very useful. We need to remember that
ft 3 means ft × ft × ft. We can use the following to cancel the ft 3 :
(2.00 ft 3 )a
12 in
1ft
ba12 in
1ft
An easier way of writing this would be:
(97.5 lb)
(2.00 ft3 g
a453.59
) 1lb b
(2.00 ft3 12 in
)a
1ft b
in
ba12 b . . . in3
1ft
(2.00 ft3 12 in
)a
1ft b
3
3456 in3 (unrounded)
In this calculation you must remember that not only are the units cubed in the
in/ft conversion, but also the numbers.
We can then add our in/ft conversion to our density calculation:
Density (Mass)
(Volume)
(97.5 lb)
(2.00 ft 3 )
g 1ft
a453.59 ba
1lb 12 in b
3
Now we have gotten to the units of g/in 3 . Since we do not have the units we are
seeking (g/cm 3 ), we need at least one more step. We can finish the problem in
one more step if we know the relationship between inches and centimeters. If