Oscillation Reaction Ideas

[encipher]

Ok,

 

I've been discussing oscillation reactions with woelen, and there are some interesting ideas using different methods.

 

This is the link to the original thread:

http://www.scienceforums.net/forum/showthread.php?t=23676

 

 

Another cool oscillation to try would be the Briggs-Rauscher Reaction.

Unlike using ferroin to be able to see the change in color, with this you get the dark starch-iodine complex, and the oscillation goes back and forth from clear to dark blue. The chemicals required for this are:

 

Hydrogen Peroxide

Potassium Iodate

Malonic Acid

Manganese Sulfate

Concentrated H2SO4

Starch

 

This list is similar to that of iodine clock reactions, so for those familiar with it, this is almost the same with oscillation. I will be making a video of this next wednesday and report the results.

 

Another interesting thing, which I tried today was a BZ reaction, except this time, I ONLY used Sodium Bromate, Malonic Acid, Sulfuric Acid, Ferroin. I tried this in a petri dish with only 5ml of solution total. My findings were as follows:

 

For some unknown reason, this experiment did not work all the time, of the 4 times I tried this, it only worked once. The only reason I can attribute to this is contamination in the de-ionized water or the petri dish. I do not know.

 

Also, the oscillation was very weird, I had started recording video footage, and for a while there was nothing, then when I put everything away and was going to clean up, the reaction began to oscillate. At least 15 mins before the start. I will be trying this again, and getting it on video soon.

 

Anyone have any ideas on other 'oscillation reactions' or thoughts regarding this one.

 

 

encipher

[woelen]

So, it seems that the bromate BZ reaction also runs without the manganese. That is an interesting observation. Could the ferroin affect the reaction. It is an indicator, but of course, it does some redox, so I can imagine that this now is the driving force for the reaction and that, due to the low concentration, it becomes very sensitive to small variations in concentrations of the other reagents. Just my idea about this.

 

I will try the BZ reaction also without manganese sulfate. I have no ferroin, but I might be able to see oscillation patterns in the bubbling of the mix.

 

Another seemingly oscillating reaction is mixing HCl 30% with H2O2 30%. When you do this, then it has periods of vigorous bubbling and periods of low activity. During the periods of low activity, the liquid seems to turns deeper green. It is somewhat fuzzy, but it looks like an oscillating reaction.

I know that HCl and H2O2 can give Cl2 and H2O, and at the same time, Cl2 and H2O2 can give H2O, HCl and O2.

[encipher]

Yeah,

 

This is what I think is going on:

 

The HBrO2 conc. begins increasing (autocatalytic reaction).. the ferroin gets oxidized to ferriin (this is were the color changes from red to blue)

 

then , as ferriin increases, it reacts and changes back to ferroin (why? I don't know.. probably has something to do with malonic acid.. but I havent completely thought it out yet) Br- is produced now, which inhibits the autocatalytic reaction. Stopping production of HBrO2.

 

And it goes on like this.. Thats the best I can come up with for now.. since the BZ reaction is quite complex and im still trying to figure out some stuff.

 

Edit: Oh, the mixture did not bubble when I did it. Maybe it is because I did it in a petri dish and it was too minute to observe?

[woelen]

I did the experiment with KBrO3/malonic acid/H2SO4, without manganese (II) sulfate added. To my surprise it did not react at all. The solution remained colorless and no gas was evolved.

 

Next, I heated the mix. When it was near boiling, a very faint red color could be observed, not like the color of bromine, but more like a purplish red. But it was very faint. Also, there was some slow bubbling.

 

Finally, while the liquid was still hot, I added a pinch of Ce(SO4)2.4H2O. At once, I obtained a fantastic oscillating reaction. Vigorous bubbling and really fast pulsing. It pulsed bright yellow two times per second or so, for several tens of seconds. It was really amazing to see this, especially because the pulsations were so fast and so clear. So, with cerium (IV) you get beautiful oscillation, better than I expected.