Diffusion and osmosis prac yr 11

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glenpaul
Posts: 25
Joined: 23 Aug 2011, 11:46
State/Location: NSW

Diffusion and osmosis prac yr 11

Post by glenpaul »

Hi
We have been doing the Heinemann 2.6 Investigation "Diffusion and Osmosis " and the part with the starch/ iodine exp has caused us some grief. I had the starch as required -5%- and loaded the dialysis tube as instructed then placed it a in a gas jar of dilute iodine/potassium sol. The starch changed colour within 5 mins but the level did not change in the thistle funnel. It is supposed to rise but it did not shift.
What are we doing wrong?
Glenpaul
RosalieM
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Suburb: Tamworth
State/Location: NSW

Re: Diffusion and osmosis prac yr 11

Post by RosalieM »

How long have you left it? From memory it takes a few days for it to be noticable. Failing that, try it with a stronger starch solution and see if that works.
glenpaul
Posts: 25
Joined: 23 Aug 2011, 11:46
State/Location: NSW

Re: Diffusion and osmosis prac yr 11

Post by glenpaul »

Thanks RosalieM
I have increased the concentration of the starch sol and it hasn't changed the level up the thistle funnel but i will keep 1 setup for a few days and see if there is any change.
RosalieM
Posts: 1795
Joined: 20 Mar 2007, 10:00
Job Title: Lab Assistant
Suburb: Tamworth
State/Location: NSW

Re: Diffusion and osmosis prac yr 11

Post by RosalieM »

It only changes by a few mm as well, so if the marker line is too thick that may make it difficult to see as well.
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smiley
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Re: Diffusion and osmosis prac yr 11

Post by smiley »

Hey Guys.

I use a 3mL disposable dropper and cut the end off the top of the bulb part. Then I insert it into the dialysis tubing and tie it off above the bulb part, so that the graduated 3 mL part extends above the tubing. That way the liquid has a much smaller diameter tube to go up, so the change is more obvious. :thumbup:
Cheers, K 8-)
RosalieM
Posts: 1795
Joined: 20 Mar 2007, 10:00
Job Title: Lab Assistant
Suburb: Tamworth
State/Location: NSW

Re: Diffusion and osmosis prac yr 11

Post by RosalieM »

Great idea Smiley! Why didn't you tell me that before I bought new thistle funnels this year? ;-)
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smiley
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Re: Diffusion and osmosis prac yr 11

Post by smiley »

Sorry! My psychic ability is limited to my child. :D
Cheers, K 8-)
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