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#### cubejunkies

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##### monolayer problem
« on: July 17, 2010, 02:48:15 PM »

So I was doing this problem here and I looked in the back to check my answer, and well... I'll just start off with the problem...

"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. This technology was pioneered by Benjamin Franklin three centuries ago. Franklin found that 0.10 mL of oil could spread over the surface of water of about 40 m^2 in area. Assuming that the oil forms a monolayer, that is, a layer that is only one molecule thick, estimate the length of each oil molecule in nanometers. (1 nm = 1x10^-9 m)"

I attempted the problem and got 2.5 x 10^1 nm, but the answer in the back of the book is 2.5 nm.

My first attempt:
0.10 cm^3/100 cm*(.10 cm^2/40 m^2)/100 cm/1x10^-9 m

My second attempt involved converting everything to meters, but once again, I had the same answer

I apologize for the obvious stupidity of this post
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#### SchrÃ¶dinger

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##### Re: monolayer problem
« Reply #1 on: July 17, 2010, 03:52:21 PM »

1)  0.1 mL is the volume of oil. First convert mL to m3.
2)  40 m2 is the area over which the monolayer extends.
3) Volume of oil = Base area * height of layer. So, find the height using the given data.

The height you obtain will be the diameter of each oil molecule (length of oil molecule refers to its diameter, I presume) in metres. Conversion to nanometers is then a piece of cake
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#### cubejunkies

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##### Re: monolayer problem
« Reply #2 on: July 17, 2010, 04:32:10 PM »

THANK YOU SO MUCH!!! I never thought to determine the height of the monolayer to find diameter, i was trying to determine molecule count and such or reduce the area to a single string and calculate that way... thank you thank you thank you!
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#### cubejunkies

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##### Re: monolayer problem
« Reply #3 on: July 17, 2010, 05:08:28 PM »

Hold on... i still didnt get the right answer :/

0.10 mL= 0.001 m^3
0.001 m^3 = 40 m^2 x height
0.001 m^3/40m^2= 2.5 x 10^-5 m
2.5 x 10^-5 m => 25000 nm

the answer is 2.5 nm in the back of the book, i have the right number but not the right decimal place
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#### sjb

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##### Re: monolayer problem
« Reply #4 on: July 17, 2010, 09:37:55 PM »

1 m3 = 103 litres = 106 ml

(edit formatting)
« Last Edit: July 17, 2010, 10:37:46 PM by sjb »
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