Reef Chemistry Question of the Day #245 Osmosis

[Randy Holmes-Farley]

Reef Chemistry Question of the Day #245

Suppose that I have a special balloon that is readily permeable to water but not to ions (like a cell membrane, but stronger).

I fill it with fresh water and drop it in a reef aquarium.

What happens?

A. The balloon gets bigger
B. The balloon gets smaller
C. There is no change in the size of the balloon

Good luck!

























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[happyschneiders]

Reef Chemistry Question of the Day #245

Suppose that I have a special balloon that is readily permeable to water but not to ions (like a cell membrane, but stronger).

I fill it with fresh water and drop it in a reef aquarium.

What happens?

A. The balloon gets bigger
B. The balloon gets smaller
C. There is no change in the size of the balloon

Good luck!

























.

The balloon gets smaller

 

[luis carreiro]

balloon gets smaller due to the ionic gradient and permeability of the balloon

 

[Grey Guy]

The balloon gets smaller because the pure water coming through the membrane will seek equilibrium, or the balloon will stay the same with no exchange, or the osmotic pressure wil make the balloon get larger. Not sure, I guess.

 

[Grey Guy]

OK I think that as pure water seeps out and increases concentration of ions, inside, then pure water will seep back inside in order to maintain equilibrium.

 

[Reef Monkie]

B.

But, if you put a balloon filled with 19999.999999 gallons of water in a 20000 gallon reef tank with 0.000001 gallons of salt water in it I don't think you are going to notice that the balloon gets smaller with the naked eye.

 

[Grey Guy]

I think it is logical that the balloon will stay the same size, if the balloon is not trying to return to a smaller size. If there is more pressure inside then out, then it must get smaller. But Randy says it’s a special balloon, which indicates to me, that there is no air or water pressure trapped inside. Therefore, the special balloon will stay the same size. The right answer is probably that it gets bigger, because that’s the one that makes the least sense. LOL

 

[Grey Guy]

O.K. You’ve really got me going on this one. Here is my final pick. The balloon will get larger because the ion density of salt water will be higher than the fresh water inside. This will force water from outside to inside, so that when the ion count is equal on both sides, the balloon will have increased in volume.

 

[KMench]

Balloon gets smaller. Water molecules migrate out of the balloon in an attempt to reach equilibrium. Since the ions can't move across the membrane the water does.

 

[luis carreiro]

I believe that fresh water has a lower osmotic concentration then salt water thus since the balloon is impermeable to ions. Water will flow from a lower osmotic concentration to one of higher osmotic concentration. Thus the balloon will get smaller

 

[redfishbluefish]

I believe the OP unwittingly added additional parameters to this problem. As an example, if I was not aware of osmosis, but realized this overfilled balloon is exerting pressure, I would come to the correct answer of B, because the pressure exerted by the extended rubber balloon forces the water out.

However, if the OP stated no pressure differences on either sides of this semipermeable balloon, than the ionic gradient would cause for water to flow from least to greatest ionic strength, thereby shrinking said balloon.....answer B.

 

[dansreef]

Smaller..... but because that monster emerald crab I put in my sump a year ago would mistaken it for the mother of all bubble algae.... and would try to munch it....

In all seriousness.... I would think that the fresh water would migrate out of the balloon.

 

[SDReefer]

The balloon gets smaller since the concentration of water outside the balloon is less than the concentration of water inside the balloon. Therefore, water will leave the balloon until the concentrations are equal. The reef tank is considered a hypoosmotic solution due to the high concentration of salt in the water.

 

[rkpetersen]

B. Much like an animal cell dropped into hypertonic saline. Except in this case and unlike with a cell, eventually there will be virtually no fluid in the balloon at all, since it can never come to equilibrium.

 

[MnFish1]

B. It gets smaller. The opposite of a freshwater dip(which causes cells to explode ich)

 

[Alfrareef]

B. Fresh water shall leave the ballon.

 

[MnFish1]

I believe the OP unwittingly added additional parameters to this problem. As an example, if I was not aware of osmosis, but realized this overfilled balloon is exerting pressure, I would come to the correct answer of B, because the pressure exerted by the extended rubber balloon forces the water out.

However, if the OP stated no pressure differences on either sides of this semipermeable balloon, than the ionic gradient would cause for water to flow from least to greatest ionic strength, thereby shrinking said balloon.....answer B.

So both ways you stated the answer was b. What was the complicating factor? Btw. If there was pressure inside the balloon and the membrane is permeable to water water would start leaking before it even hit the reef tank

 

[beaslbob]

smaller

hey only 1 chance in 3. LOL

 

[SDchris]

A or C
Devil's advocate. Pressure exerted by the salt water (depth) is greater or equal to the osmotic pressure of the two different solutes.


Chris

 

[FunkEngine]

Considering the topic title, I'm going to assume this balloon has negligible forces acting on it from pressure and elastic contraction. Water will move out of the balloon, and it will shrivel.