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September 19, 2014

Homework Help: chemisrty

Posted by bex on Saturday, February 17, 2007 at 11:48am.

if i am trying to find the diameter of an oil molecule and express my answer in scientific notation.
the info is drop of oil 0.05 cm3 from a dropper spreads out to 40 cm2
is it

vol = l x w x h
0.05cm3 = 20 x 20 xh
0.05 cm3 = 40cm2
after this im stuck as i dont know what the size of the oil molecule is
can anyone help


vol = l x w x h
0.05cm3 = 20 x 20 xh OK TO HERE.
0.05 cm3 = 40cm2 You threw away the h which is the unknown here.
after this im stuck as i dont know what the size of the oil molecule is
can anyone help
Oh, but you do know the size of the oil drop. It has a volume of 0.05 cm3 or 0.05 cc. Says so in the problem.
You have 0.05 cc = lxwxh.
The problem states that the oil drop spreads out to an area of 40 cm2. That is lxw. Now the eqution is
0.05 = 40*h
solve for h.



I think i have managed it

0.05cm3 = 40 x h
h = 0.05/ 40
h = 1.25 x 10-3cm3

is this correct please

im trying to help my daughter out on this i think i need to go back to school lol


Correct if you aren't worried about the number of significant figures. There are only two s.f. in 0.05 and two in 40 (if it is 40. and not 4 x 10^1); therefore, you are allowed only two in the answer and 1.25 has three. You must round it, if s.f. are a concern, to either 1.3 x 10^-3 or 1.2 x 10^-3 depending upon how your instructor has taught you to do it. I round to the EVEN number; therefore, I would round to 1.2 x 10^-3. A note about the 40. 40 with no decimal point after it has only one s.f., 40. has two. 4 x 10^1 has one. If the 40 has only one s.f., then 1 x 10^-3 is the answer.

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