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For a school chemistry design lab I tried to find the optimal sugar concentration for fastest yeast fermentation. I put the same amount of yeast and sugar water solutions with different concentrations of sugar together and measured the carbon dioxide produced using a water displacement apparatus. My teacher approved the topic, which is why I went along with it, but our teachers are often too lenient with approving topics, and this will be moderated so I can't just squeak through.

My main problem is that I feel it is too biology-oriented. There is very little chemistry in it. What can I do (preferably with yeast because I still have quite a bit and it wouldn't seem like a complete change of topic to my teacher)

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  • $\begingroup$ If there really is little hope, if anyone could suggest a different area or experiment I could look into that would be great. $\endgroup$
    – hm527
    Commented Jan 20, 2016 at 17:17
  • $\begingroup$ So you don't like your topic with yeast for being too biology-oriented, hence you want to switch to another topic, also with yeast? Just how would that be less biology-oriented than your current topic? Well, I guess it would if you'd kill all the yeast beforehand (say, to measure nitrogen in them by Kjeldahl method - very chemical indeed), but that's cruel and unnecessary, and not that interesting after all. $\endgroup$
    – Ivan Neretin
    Commented Jan 20, 2016 at 17:40
  • $\begingroup$ @Ivan Neretin Hi there, yeah, I see what you mean. It's hard to evade the biology-ness of yeast after all. It's generally okay for our experiments to have a mix of two sciences, but I feel that this one is really too bio-ish. If I could just have some chemistry elements I think it'd be fine. I was thinking about using yeast as a catalyst in hydrogen peroxide decomposition, but I don't know what exactly I'd be looking for (optimization?) $\endgroup$
    – hm527
    Commented Jan 21, 2016 at 3:37
  • $\begingroup$ There's really no need for me to continue with yeast, I just thought that'd be nice so that I don't have to ask my teacher for materials. I'm thinking more to find another experiment that won't require any special chemicals (just stuff like NaOH or something that the school will have on hand as our draft is due in around two weeks. $\endgroup$
    – hm527
    Commented Jan 21, 2016 at 3:39
  • $\begingroup$ A too high sugar content will give your yeast a killing osmotic pressure. Not enough other nutrients (as @Ryan hinted) will set a limit on producing capability. $\endgroup$
    – Gyro Gearloose
    Commented Jan 21, 2016 at 18:11

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It sounds like a perfect chemistry experiment to me. It sounds good enough to even be one of my AP chemistry labs. As an objective for the lab, you could try to determine the amount of CO$_2$ gas produced per amount of sugar you use, (with all other ingredients in excess). I'm pretty sure the equation for fermentation is C$_6$H$_{12}$O$_6$ → 2 C$_2$H$_5$OH + 2 CO$_2$ (although note that common granulated sugar has the equation C$_{12}$H$_{22}$O$_{11}$ and decays into two glucose molecules when combined with water).Why not test a certain amount of sugar (like .1 moles) and see if you yield the theoretical .2 moles of CO2. You could use the ideal gas laws (PV=nRT) to determine the moles of CO2 product you yielded. Compare what you yielded to the theoretical amount you should've yielded. If you yield less, then you could include in your report/conclusion including why you think your yield was short.

The lab would involve gas laws, chemical equations, and percent yield, all of which are chemistry topics/principles. What is your current level of chemistry experience? If you haven't learned of anything I mentioned, I can help explain it better and point you in the right direction if you'd like.

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    $\begingroup$ Hi Ryan, thank you for this answer. I like the idea of keeping the experiment more or less the same and having the chemistry part be in the analysis. I am familiar with percent yield and gas laws, but thank you very much for your offer. $\endgroup$
    – hm527
    Commented Jan 21, 2016 at 21:14

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