Diffusion and Osmosis | Iodine starch experiment with bag | Science Experiments | elearnin

Osmosis and Diffusion demonstration | Iodine starch experiment with bag | Science Experiments | elearnin | Chemistry demo | Diffusion and osmosis in plants explanation | Diffusion and osmosis in cells explained | Diffusion and Osmosis definitions | Diffusion and Osmosis though a semi permeable membrane

This experiment shows the movement of particles through a membrane
For this experiment you will need:
• Water
• Starch solution
• Iodine
• Dropper
• Zipper plastic bag
• Mix the starch solution in the water in a beaker.
• With the help of the dropper put some iodine solution in the zipper bag.
• Zip the plastic bag.
• Now turn up side down to check whether there is any leak.
• Submerge the plastic bag into the beaker with starch solution.
• Leave the arrangement for half an hour.
• A layer of deep purple-black color layer is formed on the membrane of the plastic bag and the color slowly diffuses into the starch water.
Iodine is used to test for the presence of starch. When Iodine reacts with starch, it turns deep purple-black.
The iodine molecules are small enough to pass through the membrane of the plastic bag, however starch and water molecules are too big to pass through the membrane.
The movement of the iodine through the plastic membrane is functionally the same as movement of molecules through biological membranes, that is, any cell membrane. The molecules will move from higher concentration to lower concentration. Osmosis is the net movement of solvent molecules (in this case, iodine) through a partially permeable membrane (like a plastic bag) into a region of higher solute (water) concentration, in order to equalize the solute concentrations on the two sides.
Here, by partially permeable membrane or semi-permeable membrane, we mean a permeable to the solvent, but not the solute.
Diffusion is that physical process in which any solvent moves, without input of energy, across a semi permeable membrane separating two solutions of different concentrations.


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  1. so the iodine diffuses into the semipermeable membrane (the plastic bag) from high concentration to low concentration meaning it doesn’t use any form of energy. when it enters the semipermeable membrane it reacts with the starch and turns a dark purple/blue/black colour. i am currently studying this and although the definition of osmosis was slightly muddled up, it was still a pretty good vid. as osmosis specifically refers to the net movement of water across a semipermeable membrane and on the rare occasion, ethanol too, the movement of the molecules actually refers to diffusion.

  2. The explanation needs to be seriously fixed. How can a wrong statement like this get thousands of views? Its too dangerous for anyone who trusts on everything they see on the internet.

  3. Osmosis is definitely NOT the net movement of solvent molecules through a partially permeable membrane into a region of higher solute concentration. Osmosis refers ONLY to the movement of WATER across a membrane from an area of higher WATER concentration to an area of lower WATER concentration.

  4. Thank you so much for making this video. It helped me alot with my biology homework. I saw this lab sheet I hadn't done (late/missing work) but this video helped me get the data I needed. 🙂

  5. I'm not quite sure if the explanation is the fact that water molecules are not small enough to make it through the membrane, because they should not be so much bigger than iodine (I would expect them to be smaller, as a matter of fact). A more plausible explanation would be that plastic, being an organic polymer, is mainly non-polar, so is iodine, which allows the latter to pass through the plastic membrane. Starch molecules are indeed too big, but water molecules do not pass through the membrane due to its polarity.

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