Homework Help: Chemistry

Posted by Amy~ on Tuesday, August 24, 2010 at 11:52am.

In water conservation, chemists spread a thin film of certain inert material over the surface of water to cut down the rate of evaporation of water in reservoirs. Franklin found that 0.10 mL of oil could spread over the surface of water of about 49 m squared in area.
Assuming that the oil forms a monolayer (one molecule thick) estimate the length of each oil molecule in nanometers.
(1nm= 1 x 10^-9 m)

I tried solving this but I'm stuck.
This is what I did 0.10/40 than /1x 10^-9 = 2.5 x10^6 as my answer

but the real answer is 2.5 nm

Could someone please write the steps to getting 2.5 nm.

Chemistry - bobpursley, Tuesday, August 24, 2010 at 12:02pm
assume the oil molecule has an area of PI(D/2)^2 where D is the length of each molecule. THen the volume of each oil molecule is area*D=PI*D^3 / 4

Total volume=49*D m^3
That is equal to the total volume of oil, .10ml=.1*e-6 m^3

so the volumes are equal
49D=.1E-6
D=.1/49 E-6=2.0E-9

I am not certain if you mean 49 0r 40m^2
Chemistry - bobpursley, Tuesday, August 24, 2010 at 12:03pm
Ignore my first paragraph. You can use that to get the number of molecules in .1ml.
Chemistry - Amy~, Tuesday, August 24, 2010 at 12:13pm
Sorry i meant 40 m squared

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