Question

Water and Iodine diffusion?

Answer 1

If I had a plastic bag with distilled water in it, and placed that bag into a cup with distilled water and iodine in it, what would happen? What color would the bag and cup turn?

Answer 2

Thanks for any help!

Answer 3

i think...plastics are pretty much impermeable to stuff....so i think there would be no change...but not vry sure....

Answer 4

Well I did the same experiment with starch in the plastic bag and the iodine diffused into the bag and turned the starch blue.

Answer 5

Sure it wasn't a semipermeable bag? ;)

Answer 6

Not sure, it was just a regular zip lock bag.

Answer 7

But let's assume it was a semipermeable bag. What do you think the color change would be for the water and iodine?

Answer 8

Iodide gives yellow in colour.

There is no change of colour when iodine is properly dissolved in water.

Answer 9

Well with that assumption I would predict that iodine would diffuse in side the bag, on gas form that is \(\sf I_{2}(g)\) which to some part would react with the water to create free iodine ions \(\sf I^{-}(aq)\). Which again would react with \(\sf I_{2}\) to form the reaction:
\(\sf I^{-}+I_{2} \to I_{3}^{-}\), where \(\sf I_{3}^{-}\) would create the blu/purple/black color. The reason for this complexity is due to membranes are impermeable for ions, but not for small gasses.

Answer 10

Thank you for all the help!

Answer 11

You do know why the dark color is being created when complexed with starch right?

Answer 12

Because the starch is too dense to diffuse through the plastic bag, but the iodine can?

Answer 13

No i meant more molecular. You know amylose create a spiral structure right? Well what iodide does is to place it self inside the spiral allowing more electron jump with frequencies in the whole spectrum that can be seen for the human eye.

Answer 14

omg...i dint know about this I3- thing...

Answer 15

Oh! That helps a lot. Thank you so much.

Answer 16

That is why as you say the starch (amylose) turn blue when iodide is nearby. Anyway no problem at all. Always fun with some biochemical reasoning. :)