Chemical Forums
Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: 1QWK96GT on November 25, 2013, 03:19:11 PM
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If you read my other post I am conducting a glow stick chemistry experiment where essentially I am making glow stick solution. http://www.wikihow.com/Make-a-Glowstick After I make four solutions for two examples. the one hydrogen peroxide and distilled water mixture got put on a hot plate and dumped into the luminol, soldium carbonate, ammonium carbonate, distilled water solution. The hott solution glowed longer than the cold one. My teacher said that the cold one was brighter though. I can not explain why? I expected the hot one to be brighter but not last as long as the cold one. but really the hot one lasted longer and the cold one was brighter. This makes no sense to me. HELP.
Thanks,
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This makes no sense to me. HELP.
It makes no sense to me, either. Are you sure your teacher's observation was correct?
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Im not so sure his observations are correct. I know for a fact the hott one lasted longer but to say the cold one was brighter is the part i dont think is the case. Would that make sense.
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In most cases, a higher temperature results in a faster reaction. The luminescence intensity should correlate in some fashion to the product turnover rate (concentration of products per unit time, say). Therefore a higher temperature should results in a more intense but shorter lasting luminescence. This is exactly what you see if you put commercial glowsticks in the freezer: they will last a lot longer, but will be a lot dimmer as well. I would expect the luminol reaction to behave in a similar fashion, although I haven't verified this.
Assuming the observation is correct, and that the luminol reaction behaves in the way described above, there are two possibilities for the discrepency:
(1) Error in measurement. There is a reason we use a spectrofluorimeter to measure luminescence in a laboratory setting instead of our eyes. Likewise, how are you measuring "duration"? And how are you controlling temperature? To really compare these conditions, you would need to do the experiment carefully, and measure the fluorescence kinetics using a calibrated photon detector.
(2) Statistical anomaly / error in method. You've only taken one measurement. Do it several times and see what the average result is. There might be errors in the starting material concentrations, for instance.
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I think there is an error on the calculations maybe "I recalculated the amount needed which I figured .4grams of Copper Sulfate would be about .31 grams of Cupric Sulfate Pentahydrate." I dont know how to get the correct amount of cupric sulfate pentahydrate
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I would assume the procedure calls for pentahydrate, anhydrous copper sulfate is rather rare.
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The original formula I am using is this: http://www.wikihow.com/Make-a-Glowstick It states to use ".4 grams of copper sulfate" but in our lab we only had cupric sulfate pentahydrate. My teacher said I could substitute it instead but I dont know what to change the quantities to.
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It states to use ".4 grams of copper sulfate" but in our lab we only had cupric sulfate pentahydrate. My teacher said I could substitute it instead but I dont know what to change the quantities to.
Have you read what I wrote? You don't have to change the quantity, as most likely procedure calls for copper sulfate pentahydrate (even if it mentions just a copper sulfate).
Using anhydrous copper sulfate just to dissolve it in water would be a waste, as anhydrous is more expensive and it will get hydrated after adding it to water.
Besides, the difference in mass between anhydrous and pentahydrate is not that high, I doubt it is wrong concentration of copper sulfate that is a problem. You are right about your calculations being wrong though - mass of pentahydrate should be higher than the mass of anhydrous salt.
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Okay I understand now. Sorry I was misunderstanding you. Thanks for all the help. :)