Does anyone clearly understand osmotic pressure?

[MCAT guy]

So osmotic pressure is the pressure I must apply to prevent osmosis by a pure solvent. E.g. it is the pressure I need to apply on the far right of this U tube to bring the 1M saline solution even with the pure water...

What I'm not understanding is, does this osmostic pressure actually exist when i don't apply this pressure. We talk about osmotic pressure causing or preventing fluid flow in blood, but the osmotic pressure in these examples is the amount of pressure I have to put on the 1M saline to eliminate the delta, so it appears that osmotic pressure isn't actually there...

Does anyone clearly understand this idea?

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[MCAT4life]

So osmotic pressure is the pressure I must apply to prevent osmosis by a pure solvent. E.g. it is the pressure I need to apply on the far right of this U tube to bring the 1M saline solution even with the pure water...

What I'm not understanding is, does this osmostic pressure actually exist when i don't apply this pressure. We talk about osmotic pressure causing or preventing fluid flow in blood, but the osmotic pressure in these examples is the amount of pressure I have to put on the 1M saline to eliminate the delta, so it appears that osmotic pressure isn't actually there...

Does anyone clearly understand this idea?

I think your pictures might have confused you, but from what I learned, osmotic pressure is the pressure it would take to STOP osmosis from occuring. So when you have steady osmosis (net flow of water from area of low concentration of solute, to an area of higher concentration of solute, in order to dilute the higher solute concentration.) If you wanted to stop this natural osmosis, you would have apply pressure to the area with the higher solute concentration. (the formula (Osmotic pressure = MiRT) shows you that the lower molarity (1M saline) the less osmotic pressure is required to stop osmosis. (this should make intuitive sense since at lower solute concentration , water would not flow as rapidly to try and equilibrate out both sides. You can't really say that because there is less Osmotic pressure required, that there is in a sense a internal osmotic pressure because it is the net flow of water that has decreased as molarity is decreased on the side where osmotic pressure is applied.

If anyone has a better explanation for this one I would love to hear it as well.

 

[loveoforganic]

MCATs both with 46 and same registry. Freaky

 

[MCAT4life]

talking about freaky lol.. and having a sharp eye for catching lol.. anyways, I figure you'd have something to add on my explanation being a (Chem fanatic and all!) so I guess my explanation was ok after all 🙂

 

[fizzgig]

So osmotic pressure is the pressure I must apply to prevent osmosis by a pure solvent. E.g. it is the pressure I need to apply on the far right of this U tube to bring the 1M saline solution even with the pure water...

What I'm not understanding is, does this osmostic pressure actually exist when i don't apply this pressure. We talk about osmotic pressure causing or preventing fluid flow in blood, but the osmotic pressure in these examples is the amount of pressure I have to put on the 1M saline to eliminate the delta, so it appears that osmotic pressure isn't actually there...

first note that the picture is a time lapse (might be obvious to everyone else but i had a moment of confusion). start with 2M and water exerts a force (wants to move over to saline side). the flow slows and stops as the building hydrostatic pressure goes up, til the osmotic pressure (how much water wants to move ) equals the hydrostatic pressure of holding one column of water higher than the other.

yes, the osmotic P is the force you'd have to apply to prevent any water movement, so the force of the displaced water column in (c) is that force. you could apply that force to (a) to begin with and if you held that pressure in place no movement would take place. (i believe)

yes, even if you don't do anything that force 'still exists'. if the osmotic force didnt continue to exist then the extra column of fluid wouldn't have anything holding it up anymore. gotta have equal and opposite force for static equilibrium.

ppl feel free to correct if i misstated anything.

 

[MCAT guy]

first note that the picture is a time lapse (might be obvious to everyone else but i had a moment of confusion). start with 2M and water exerts a force (wants to move over to saline side). the flow slows and stops as the building hydrostatic pressure goes up, til the osmotic pressure (how much water wants to move ) equals the hydrostatic pressure of holding one column of water higher than the other.

yes, the osmotic P is the force you'd have to apply to prevent any water movement, so the force of the displaced water column in (c) is that force. you could apply that force to (a) to begin with and if you held that pressure in place no movement would take place. (i believe)

yes, even if you don't do anything that force 'still exists'. if the osmotic force didnt continue to exist then the extra column of fluid wouldn't have anything holding it up anymore. gotta have equal and opposite force for static equilibrium.

ppl feel free to correct if i misstated anything.

Thanks guys, I understand this idea better now.