# Homework Help: Finding volume content

1. Oct 9, 2011

### ibysaiyan

1. The problem statement, all variables and given/known data

The question is as following:

2. Relevant equations

3. The attempt at a solution

I have absolutely no idea on how to solve this problem. Usually problems indicate some quantity which we can substitute into an equation.
Any tips will be greatly appreciated.

2. Oct 9, 2011

### cepheid

Staff Emeritus
You know that the amount of oleic acid in the final mixture is 1 part in 400. So all you have to do is figure out the volume of a single droplet, and the volume of oleic acid in that droplet will be 1/400 of that droplet volume.

So, what is the volume of a droplet? Well, 97 droplets have a volume of 1 cm3, so 1 droplet has a volume of ____?

3. Oct 9, 2011

### ibysaiyan

Hm will it be 1/97 cm$^{3}$ , if so then would I multiply this fraction by 400 ?

4. Oct 9, 2011

### cepheid

Staff Emeritus
That's right.

5. Oct 9, 2011

### ibysaiyan

Thank you very much! The wording of the question brought about confusion to my mind.This question has another parts as well, which I'll try to solve.

6. Oct 9, 2011

### SteamKing

Staff Emeritus
Are you sure multiplication by 400 equals the correct volume of oleic acid?

7. Oct 9, 2011

### ibysaiyan

Volume of oleic acid in one droplet ?
why is it wrong ?

8. Oct 9, 2011

### SteamKing

Staff Emeritus
Because the oleic acid was being diluted in methanol.

9. Oct 9, 2011

### cepheid

Staff Emeritus
Yeah, sorry, I missed that. I thought he meant multiply the denominator by 400 (i.e. multiply by 1/400 just the way I told him to).

10. Oct 10, 2011

### ibysaiyan

Oh I see.. I initially thought of multiplying by 1/400 , i even had that posted as an answer until I changed my mind.Some misunderstanding from both ends. Now it's clear. Thanks.

11. Oct 10, 2011

### ibysaiyan

So here's my final answer for this question: 1/97 x 1/400 ~ 2.6x10^-5 cm3

The questions which follow on are:

The surface of a tank of water is dusted with fine powder. A single drop of the
diluted mixture is allowed to fall on the water surface. The alcohol component mixes
with the water and the oil forms a monolayer film on the water surface, displacing
the dust so it is clearly visible, with a diameter of 9.4 cm. What is the thickness of
the film?

I have answered this: All that was needed to be done was using the Volume = Area x thickness.My final answer is: 3.7x10^-7 cm.

Next question's:
The shape of an oleic acid molecule can be approximated by a cuboid l ´ l ´ 7l .
One end (COOH) loves water (hydrophilic) and the other end hates it (hydrophobic).
Assume that these molecules stick out of the water and form a monolayer close
packed in a square arrangement. What are the dimensions of the molecule?

What does the statement which I have highlighted in bold mean ? do I find out the unit dimension of the molecule? I know lxlx7l denotes volume of the molecule.

Last edited: Oct 10, 2011
12. Oct 10, 2011

### ibysaiyan

Never mind I have found the answer for this. Thanks everyone for your help!

13. Oct 10, 2011

### ibysaiyan

I need a quick tip on how to solve one of the last bit of this question. The question basically wants me to derive Avogadro's number of oleic acid. So the molecular mass I have got is : 282.
Now I know moles = Mass/ Mr.
To get mass I will have to use density = Mass/ volume.
But once I sub in the numbers.. I get something in the range of 5x10^24! :(

My volume for oleic acid in one droplet was: 2.6x10^-5 (cm3 , do i divide this by 100 to get m3, or is it 1x10^-6 ? )
Density in the question is given to be 890 kg/m3.

Any help will be much appreciated. Thanks!

14. Jan 29, 2012

### Jessefisser

How do I find out the volume of something that is 36w - 16h - 16d. Would it just be 36 * 16 * 16.