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4D50.70 - Osmosis

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​4D50.70 - Osmosis

Title4D50.70 - Osmosis

Illustrate the tendency of a solution of given concentration to pass though a semi-permeable membrane into a solution of lower concentration, thereby equalizing the concentration of solvent on both sides of the membrane.

Assembly Instructions

The thistle can be stored with the membrane on it, so it may be usable off the shelf. If the membrane is damaged or ineffectual, see the construction instructions to replace it.
The membrane must be tightly secured to the thistle (with many rubber bands) or the osmosis will take place where water meets instead of through the watertight membrane.
Pour "plain" water (spring or distilled, not Dennison) in to the large beaker until about half full. Position the silver clamp on the rim of the beaker and above the jar.
Pour hot water into a mixing beaker. Mix in sugar until you have a saturated sugar/water solution (until the water won't dissolve anymore sugar). Add dye to the solution (for visibility).
Insert the pour rod into the thistle (don't puncture the membrane) and add enough dyed syrup to be level with the water, but do not place in the water yet (or you'll start the process).
When you're ready to start the osmotic process, place the full thistle in the plain water beaker. This process takes ~30 minutes.

Setup Time20
Operation Time
Preview Time5
Operation Instructions

Operation Steps
1   Put the full thistle into the plain water.
2   Notice that the level of the dyed soln is approximately the level of the water. (adjust if needed)
3   Wait ~30 minutes, you should see that the level of the dyed water has risen due to osmosis.
This demo takes on the order of ~30 minutes to run, so it is advisable that you start it at the beginning of class so the results will be noticable.

Demo on DimeNo
PIRA 200No
Export Instructions (if different)
Category4 Thermodynamics
Subcategory4D - Kinetic Theory
Keywordsfluid flow, osmotic pressure
Construction Information
To put a new membrane on the thistle: First soak the membrane until it becomes soft and pliable. After it has been soaked enough, cover the funnel of the thistle tube and tuck the edges of the membrane against the funnel's lip and secure tightly with many wraps of rubber band until airtight.
beaker 2000 mL glass
glass thistle tube
membrane - potato, dialysis tubing
thistle pouring rod
sugar solution
water - from the tap
thistle membrane clamp