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My partner and I must do a demonstration for our AP chemistry class on 3/19. We have chosen to do a breathalyzer reaction. We are going to compare how the indicator reacts with vodka to its reaction with beer. We have all the materials, and we have followed the directions carefully. However, we have had major problems getting the reaction to occur quickly and noticeably enough.

We have had problems with step 3 (getting the gel) and 16 (making the reaction happen). Initially, the reaction was slow. The mixture we used was supposed to turn from orange to green. Instead, it turned from yellow to clear with some blue tints, taking over ten minutes to complete. After experiencing this twice, I added a few more drops of potassium dichromate and was able to make the gel orange. When I added ethanol (about five drops of vodka), the reaction was slightly more noticeable. Putting several drops of the ethanol directly onto the gel changed it to green/blue in a minute or two. This was better, although still not fast enough. My partner and I tried again to see if we could make the reaction faster by adding even more potassium dichromate solution. Instead of obtaining the desired orange gel as I had done before, the mixture was mostly a yellow liquid with only slight gelling. Adding more sulfuric acid and sodium silicate did not seem to help. My partner and I need to get the reaction working well very soon so that we can have an interesting demonstration for the class. We are looking for a gel that will completely turn green in a pipet in about a minute when ethanol from a balloon is blown into it. We would like to compare this with adding beer through the balloon. Why did the mixture stop gelling and turning orange despite all the trials and adjustments? What can we do to get an orange gel that will work well, as I described?

Question Date: 2003-03-15
Answer 1:

Thank you for your careful description of your problem. Often times being careful is the key to scientific success.

Having said that, I'm afraid that I do not have a clear answer to your problem, but you may wish to consider the following items. Your difficulties seem to be largely in that the rates of certain chemical reactions are not as high as you need them to be. You might want to think about what makes reactions go faster. Some things include: increasing temperature, increasing concentration, and changing pH. By varying these (and perhaps other parameters) you may be able to get the reaction to work.

Even if these things don't work, you might want to keep them in mind for future cases where you need to accelerate reactions.

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