# Osmosis Help Me Out

1. Apr 19, 2005

### dagg3r

Hey guys can someone help me with the osmosis scenarios and rank them in order of the most mass gained and also write a good definition of what osmosis is thanks.

thanks

first of all i have the following solutions
i have 5% sucrose in dialysis tube in distilled water - cup 1
i have 10% sucrose in dialysis tube in distilled water - cup 2
i have 20% sucrose in dialysis tube in distilled water - cup 3
i have 20% sucrose in (0.9% nacl solution - cup 4
i have 5% nacl in distilled water - cup 5

my definition of osmosis is what it think is the net movement of water molecules from area of high concentration to low concentration.

normally i would expect the higher concentration in the dialysis tube the more it will gain in mass but i got confused with the 5% nacl in distilled water and 20% sucrose in 0.9% nacl, i dont know which is more concentrated but would i assume 20% sucrose in 0.9% nacl isotonic??? please rate the order you guys think from less increasing mass - most increasing mass i will have a shot and chose.

THE ORDER from 1 (lowest increasing mass ) to 5 ( most increasing mass)

1. cup 4
2. cup 1
3. cup 2
4 cup 5
5. cup 3

thats my guess is that right?

2. Apr 19, 2005

### kusal

The percentage is given considering the weight its the molarity that is conserned when it comes to osmoasis.
molarity of 0.9% NaCl is much higher than 20% sucrose.

And your definition of osmoasis is wrong.9you have to mention the semi permiable membrane)

3. Apr 19, 2005

### Moonbear

Staff Emeritus
As kusal mentioned, in your definition, you need to account for diffusion through a membrane.

I'm confused by the way your question is set up. Do cups 4 and 5 also have the sucrose or NaCl solution inside dialysis bags? Are you supposed to measure the mass gained inside the dialysis bag?

Since the NaCl solution is what is confusing you, keep in mind that dialysis bags are semi-permeable or selectively permeable. Small, water soluble ions, such as Na+ and Cl-, can pass through the membrane, while larger molecules, such as sucrose can't. How does that change your predictions?

4. Apr 19, 2005

### misskitty

Moonbear, this is related to what you said about the mass a bag would gain. Would it be possible for a solution to undergo osmosis and decrease in concentration? I don't know if that makes sense. I mean if you had NaCl dissolved in H2O and it undergoes osmosis and what you get after the osmosis is complete would have a smaller concentration of NaCl than before? I don't think that makes sense....I just confused myself...grrr...

5. Apr 19, 2005

### Moonbear

Staff Emeritus
You're right. That's exactly the point with osmosis. You're selectively mixing two solutions, one on each side of a membrane. The net flow of water is in one direction. So, on one side of the membrane, concentration of your solutes increases and on the other side it decreases until equilibrium is reached. That's why cells also need methods of active transport, otherwise, once equilibrium was reached, nothing else would happen. They need a way to pump stuff against the concentration gradient to maintain polarity across membranes in order for the cells to function properly.

6. Apr 19, 2005

### misskitty

Oh ok. Would it ever filter out so much of the solution it could 'clog' or 'plug' a few of the spaces where water flows from the higher concentration to the lower concentration because the cell didn't properly 'clean' the openings? I don't think those are the right terms. :uuh: