I was looking at a few videos online.

Question

I was looking at a few videos online.

If you type in "top ten amazing chemistry videos" into google and click the first link (wired science), you'll see what I'm speaking of.

Well the thing is, I'm curious about the rxn in video # 6.

It was described as "mysterious rxn creates undulating brew". I thought that the rxn was a equillibrium rxn of some sort since the "mystery" of it is that it like the title suggests, undulates from blue-black to colorless all on it's own whilst heating. After the video ends, or you just fast foward since I got the point of the rxn after a few color changes, there are a few rxns like that suggested for viewing and one has this man actually saying what is used. I read the bottom of the page where I showed you how to go to and someone suggested it was a "iodine clock rxn". Problem with that is, yes it does look like that but when you look up videos on that site it shows just one color change. I only found 2 rxns that matched the one I saw for #6 and it's apparently called Briggs Rauscher Oscillating clock rxn.

I'm curious to know why that rxn which is similar to the iodine clock rxn but shifts from products to reactants all on it's own happens and why the iodine clock rxn only has a color change once. I assume it's something added to one rxn and not the other but from what I saw, there are actually a few ways to do the rxn...but do they lead to different results?

Oh and I think you would be interested in viewing the other 9 video's on that site. I thought they were fun to watch.

Thanks Dr.Bob

2 answers

I didn't look at the video but from what you describe it is the iodine clock reaction. I've never done the iodine clock but I have seen it done and I have seen the chemistry (but I don't remember the chemistry very well). Anyway, from what I've seen and read, I understand that the number of times the iodine clock changes color from colorless to black to colorless etc is controlled by the amount AND concentratins of the reactants. I understand, also, that it takes a little time and patience to hit the right combinations. It usually wows grade school and high school students. Thanks for bringing this to my attention. I will look at it sometime but right now I'm packing to take a trip. This is a quick break for me.

Oh..Have fun Dr.Bob =D

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DrBob222 · Answer

I didn't look at the video but from what you describe it is the iodine clock reaction. I've never done the iodine clock but I have seen it done and I have seen the chemistry (but I don't remember the chemistry very well). Anyway, from what I've seen and read, I understand that the number of times the iodine clock changes color from colorless to black to colorless etc is controlled by the amount AND concentratins of the reactants. I understand, also, that it takes a little time and patience to hit the right combinations. It usually wows grade school and high school students. Thanks for bringing this to my attention. I will look at it sometime but right now I'm packing to take a trip. This is a quick break for me.

~christina~ · Answer

Oh..Have fun Dr.Bob =D