Thistle funnel osmosis demo - help!

Hi everyone,
New to the forum so hopefully I've posted this in the right place!

I'm trying to set up the osmosis demo and failing.. No matter what concentration sucrose I use, the level doesn't seem to go up?
What concentration of solution do others use to get this demo to work?

Thanks in advance,
Sara
 
Hi everyone,
New to the forum so hopefully I've posted this in the right place!

I'm trying to set up the osmosis demo and failing.. No matter what concentration sucrose I use, the level doesn't seem to go up?
What concentration of solution do others use to get this demo to work?

Thanks in advance,
Sara
I've used a capillary tube and a bung with knotted visking over it.
 
Does the visking work if you put some sucrose solution in the whole tubing and suspend it in a beaker of water? I would suggest making the sucrose solution as concentrated as you can. 1molar would be a good start.
 

karen b

COMMITTEE
How do you cheat? :D

I'm not the biology technician and just read that you were using visking tubing. Having just looked for images of the set up I see it is slightly different to when we use visking tubing so might not be the same experiment at all
 
Capillary tube through a rubber bung
visking tubing on bung (o/s diameter slightly smaller than the visking tubing) held by several twists of elastic band, knotted at bottom filled with coloured 1M sucrose solution.
Place in beaker of distilled water. As below works every time. The rubber band on the capillary tube is optional and there only to mark the level of the sugar solution,
upload_2019-2-19_8-51-1.png
 
That's the same experiment using slightly different apparatus. Not a thistle funnel so that students can do it, presumably, and a capillary tube so that results appear more quickly and dyed solution so that the results can be seen more clearly.

Even with a non-capillary thistle funnel, I would expect to see a result in an hour or so.

In the original setup, do you start with the sucrose solution level in the thistle funnel above the water level? How long do you leave it?
 
Capillary tube through a rubber bung
visking tubing on bung (o/s diameter slightly smaller than the visking tubing) held by several twists of elastic band, knotted at bottom filled with coloured 1M sucrose solution.
Place in beaker of distilled water. As below works every time. The rubber band on the capillary tube is optional and there only to mark the level of the sugar solution,
View attachment 2523

This is exactly what I set up, and yes, it always works :)
 
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