Fermentation experiment (1 Viewer)

[Trebla]

Hi guys,
I have a question regarding the fermentation experiment we had to do. I am aware that to promote fermentation we need low oxygen and a relatively high temperature (around 30 degrees celsius). The thing is that when our class did it, we did not even consider the required temperature. We basically had a sealed side arm flask with all the contents and a tube attached to it leading to a beaker of limewater. We left it in the lab at room temperature for a week. I am also aware that some other schools carry the process out by putting cotton wool over a normal flask and leaving it in an incubator, which seems more valid. So in the HSC exam, if I write what we really did, would I lose marks?
Thanks

 

[Riviet]

So in the HSC exam, if I write what we really did, would I lose marks?

In some cases you would, especially if your method is invalid. The advice I've been given by my chemistry teacher who's marked past HSCs is to pretend you did the prac properly and write down the procedure and results etc. that you are supposed to obtain from the prac.

 

[priesty]

In some cases you would, especially if your method is invalid. The advice I've been given by my chemistry teacher who's marked past HSCs is to pretend you did the prac properly and write down the procedure and results etc. that you are supposed to obtain from the prac.

very true. do whatever you can to gain marks. even if you memorise what was supposed to be done/or what is supposed to occur. it's hard to just write it down considering that you may not have done the practical accurately, but thats the only way. last year, i was absent for a while and ultimately missed out on a few practical lessons.... i had to memorise methods and understand discussions without even having done the prac. if you understand the logic and theory behind it, then it shouldnt be too hard.

 

[Trebla]

OK thanks for that....
That means in the trials I have to use our method, but in the HSC I would have to use the other method....

 

[priesty]

yep exactly... haha

 

[tristambrown]

you could state what you did and in your conclusion state what you could have done to make it more accurate .. ie should have controlled temp etc etc

knowing what you should have done is just as valid (if not more valid) than having done it properly as told by someone else

 

[chi-es]

i wish i read that earlier cause i forgot what the expriment we did as a class and so, i sorta did what another school did and the teacher was like "umm... not sure if that's what we did in class....". ( but i still got the marks ).
Speaking of the fermentation expriment, ummm... does anyone know if ther are any tests to identify that ethanol was one of the products????
hehehe... i sorta have an assignment due tomorrow.....:mad1:

 

[dhampoet]

Hi
How to calculate the ethanol produce from the result of loss of CO2?

 

[idling fire]

chi-es (if its not too late lol) - A test for ethanol is fractional distillation of the products (ethanol comes off at about 70 degrees), then you can test by combustion, smell, or using acidified potassium permanganate as an indicator (decolourises from purple to clear).

dhampoet - From the volume of carbon dioxide collected, divide by 24.79 (moles to volume ratio at room temperature) to find the number of moles of carbon dioxide produced. Now compare to the balanced equation of fermentation. From this equation, the number of moles of carbon dioxide is equal to the number of moles of ethanol produced. So the number you calculated is how many moles of ethanol you have.