diffusion and osmosis edexcel core prac 4 demo

I'm struggling to get this to work. I'm sure I have secured the bottom of the visking tubing ok, but think I'm not getting it right at the joining of the tubing to the capillary tube. I have tried several techniques and have tried the suggestions I found on here, but to no avail.
Any further help/suggestions would be welcome!
 
I'm not sure which practical you are doing. If it is a simple demo of osmosis then I find the best way to fix the visking tubing to the capillary tube is by using a single hole bung that you can just slip the tubing over then using elastic/rubber band to fix it to the bung.
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Attach the knotted visking tubing on the bung (with the elastic - twist and loop over several times) and, using a syringe, fill it right up to overflowing with strong sucrose solution (at least 1M) with a little food colouring (getting all the air out). Then insert the capillary tube into the bung (making sure there is no air in the tubing bag). Holding the bung, slide the capillary tube to get the solution showing about a quarter of the way up. Fully immerse the tubing in a beaker of distilled water without it touching the sides (so use a full 600ml beaker) and so the whole thing is held in position by a clamp.
You will actually see the fluid rising up the capillary tube and it will pour out of the top within half an hour. So setting up time is crucial to get a result in the lesson.
I have found that if you take it out of the water it will stop and resume if you put it back in, giving you some leeway with timing to enable the students to view it in action.
 
I'm not sure which practical you are doing. If it is a simple demo of osmosis then I find the best way to fix the visking tubing to the capillary tube is by using a single hole bung that you can just slip the tubing over then using elastic/rubber band to fix it to the bung.
View attachment 4402
Attach the knotted visking tubing on the bung (with the elastic - twist and loop over several times) and, using a syringe, fill it right up to overflowing with strong sucrose solution (at least 1M) with a little food colouring (getting all the air out). Then insert the capillary tube into the bung (making sure there is no air in the tubing bag). Holding the bung, slide the capillary tube to get the solution showing about a quarter of the way up. Fully immerse the tubing in a beaker of distilled water without it touching the sides (so use a full 600ml beaker) and so the whole thing is held in position by a clamp.
You will actually see the fluid rising up the capillary tube and it will pour out of the top within half an hour. So setting up time is crucial to get a result in the lesson.
I have found that if you take it out of the water it will stop and resume if you put it back in, giving you some leeway with timing to enable the students to view it in action.
Thanks Peter, I think my error was not filling up the visking tubing enough, as I was losing liquid trying to attach it. What i.d is your capillary? I wonder if mine is too small.....I wouldn't easily refill from the capillary
 
Thanks Peter, I think my error was not filling up the visking tubing enough, as I was losing liquid trying to attach it. What i.d is your capillary? I wonder if mine is too small.....I wouldn't easily refill from the capillary
The internal diameter shouldn't make any difference apart from speed the liquid moves up (I think mine is 0.5mm) - You don't 're-fill' from the capillary tube, if you make sure the tubing bag attached to the bung is as full as possible and hold it with the bung whilst pushing the capillary tube onto the hole, the fluid will appear in the capillary tube and you can adjust it by sliding it further into the bung to move the fluid up or pull it out to lower.
 
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