# Help me, please

#### physicsss

I'm having trouble with this problem below:

1000 cm^3 of oil is spilled onto a smooth lake. If the oil spreads out uniformly until it makes an oil slick just one molecule thick, with adjacent molecules just touching, estimate the diameter of the oil slick. The diameter of the oil molecules have a diameter of 2 X 10^-10 cm.

Here's what I did.

Volume of the slick = pi*r^2*h
1000 = pi*r^2*1 (since it is just one molecule thick)
r = 17
d = 34

Now do I multiply 34 by 2 X 10^-10 cm to ge the diameter of the oil slick?

Thanks so much.

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#### Chronos

Gold Member
Count the total number of molecules. Use that number as the values for A in the area of a circle formula (A = pi r^2) then solve for r. After that, multiply by the molecule size. By the way, [1000cm^3 = 10 x 10 x 10 cm cube], you should come up with a very big number.

#### needhelpperson

go to this link. Basically the same question was asked, except they used different measurements. I'm wondering, are you both in the same class?

Besides that, when you said 1 molecule thick, you should actually use the units given for the height of that 1 molecule. Otherwise you'll have to divide the answer that you have by sqrt(2*10^-10)....

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#### physicsss

How do you count the number of molecules?

#### needhelpperson

physicsss said:
How do you count the number of molecules?

nm that, you are using the correct procedure. Just that if you want your answer in cm, read what i've posted.

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#### physicsss

OK. So 1000=pi*r^2*100(2*10^-10)
r= 1 X 10^5

Is that and the sig fig right?

#### Chronos

Gold Member
If each molecule is 2 x 10^-10, it takes 5 x 10^9 [1/(2 x 10^-10)] molecules aligned end to end to make a chain 1 cm in length. Cube that and you get the number of molecules per cc.

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