# Math problem but from Chemistry class..

• Sep 20th 2010, 09:35 PM
butters
Math problem but from Chemistry class..
This is actually from my Chemistry class, it's a word problem with basic algebra, so think it belongs in this section.

Here's the problem:

The aluminum in a package containing 75ft^2(2 is for square) of kitchen foil weighs approximately 12 ounces. Aluminum has a density of 2.70 g/cm^2. What is the approximate thickness of the aluminum foil in millimeters? (1oz = 28.4 g.)

I'm getting the answer 0.5521mm. But apparently, that's wrong (according to the book). The solution in the answer key is 1.8 x 10^-2mm.

Here is what I did:
I divided the volume by the area; logically, that should give me the thickness:

340.8g / 2.70g/cm^3 = 126.22

75ft^2 (100cm^2 / 3.281ft^2)

126.22cm^3 / 2285cm^2 = 0.055221cm

0.05521cm x 10mm = 0.5521

Tell me where I went wrong...
• Sep 20th 2010, 09:53 PM
Mollier
Hi,

75ft^2 is 69700cm^2.
• Sep 20th 2010, 11:32 PM
butters
Quote:

Originally Posted by Mollier
Hi,

75ft^2 is 69700cm^2.

I don't follow what you did there.
According to the book, 100cm equals to 3.281ft.

How are you getting 69700cm^2 ?
• Sep 20th 2010, 11:43 PM
Mollier
Hi mate,

if $100cm = 3.28ft$

then

$100^2cm^2 = 3.28^2ft^2$

$(100^2cm^2/3.28^2ft^2)*75ft^2 \approx 69700cm^2.$