Calculate Height Difference Given Osmotic Pressure

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Discussion Overview

The discussion revolves around calculating the height difference a column of water would be raised due to osmotic pressure. Participants explore the relationship between osmotic pressure, gravitational force, and the dimensions of the water column, considering various factors such as density and cross-sectional area.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant calculated osmotic pressure using the formula (nkt/V) and seeks to determine the height difference it would create in a water column.
  • Another participant suggests using the equation P=ρgh to relate pressure, density, gravitational acceleration, and height, noting the gravitational force as 980 dynes.
  • Some participants express uncertainty about the density of the solution and inquire if there are alternative methods to calculate height without it.
  • There is a discussion about the impact of concentration changes in the solution as water moves across the membrane.
  • One participant posits that the density used should be that of water, assuming an unlimited solvent, and questions how the cross-sectional area would affect the height calculation.
  • Another participant reiterates the importance of the cross-sectional area in the context of the problem, emphasizing the phrasing of "a column of water."

Areas of Agreement / Disagreement

Participants do not reach a consensus on how to proceed with the calculation, particularly regarding the role of density and the effect of cross-sectional area. Multiple competing views remain on these aspects.

Contextual Notes

Participants note the lack of provided density for the solution, which complicates the calculations. There is also mention of changing solution concentration during the osmotic process, which may affect the outcome.

kthejohnster
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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.
 
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I guess it would have something to do with P=ρgh
Pressure = density x g x height, g= 9,81m/s^2 (980 dynes)
 
256bits said:
I guess it would have something to do with P=ρgh
Pressure = density x g x height, g= 9,81m/s^2 (980 dynes)

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:
When water moves across the membrane the solution concentration changes so you have to take that into account.
 
the question asks for the affect of the amount of pressure (maybe so we avoid taking conc changes)
 
kthejohnster said:
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

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 separated 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.
 
kthejohnster said:
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
It says "a column a water", doesn't it?
 

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