# Osmotic pressure

1. Oct 23, 2011

### kthejohnster

i calculated osmotic pressure of a solution (nkt/V) and now i need to figure out how high this pressure would raise a column of water with a cross sectional area of 1cm^2. The force of gravity given is 980 dynes. How would i figure out height difference, i know it has to do with pressure difference but not sure how.

Last edited: Oct 23, 2011
2. Oct 23, 2011

### 256bits

I guess it would have something to do with P=ρgh
Pressure = density x g x height, g= 9,81m/s^2 (980 dynes)

3. Oct 23, 2011

### kthejohnster

thanks but i wasnt given density of the solution is there any other way?
i believe it has to do with cross section because next part asks for answer if cross section is 10^6 cm^2

Last edited: Oct 23, 2011
4. Oct 23, 2011

### Curl

When water moves across the membrane the solution concentration changes so you have to take that into account.

5. Oct 23, 2011

### kthejohnster

the question asks for the affect of the amount of pressure (maybe so we avoid taking conc changes)

6. Oct 23, 2011

### 256bits

As an aside, if you prepared your solution to a given molarity then you can find the density of the initial solution, but as the osmotic process continues the solution concentration will change.

Since the question asks for how high the osmotic pressure of the solution would raise a column of water of a area A, then I would assume the density used would be that of water.

Right now I don't see why a difference in the area would change the answer. Assume an unlimited amount of solvent seperated from the solution by the semi-permeable membrane. The solution would rise h above the surface of the solvent ( water ).

I hope I am not missing something just so basic that I do see it.

7. Oct 23, 2011

### nasu

It says "a column a water", doesn't it?