Alcoholic fermentation question. (1 Viewer)

[Nezuko----]

Hi! So I recently got a prac for chem and was confused (I mean really confused) on a method for the fermentation of glucose, the necessary equipment to carry out an experiment and the required calculations to fulfil the aim.

The aim is to determine the amount of ethanol produced due to the fermentation process.

Do you guys have any ideas? Thanks!

 

[LennonTheLemon]

For fermentation to occur, you MUST have the following conditions:

• an anaerobic environment --> this forces the yeast to produce ethanol as opposed to ATP when they try to respirate (similar to how your body produces lactic acid when you are running on low oxygen)
• The reaction container should be 35-40 degrees celcius (but this can vary)
• You need yeast as they naturally produce zymase, an enzyme (biological catalyst) that speeds up the process by binding to glucose
• Your solution must be aqueous --> this creates a "concentration buffer" (if you will) for ethanol, basically increasing how long the yeast can live for before the alcohol poisons and kills them; usually, the maximum ethanol you can attain is 75% w/v becuase the yeast die after that.

The only reactant you need is glucose. I'm not sure if you're meant to make your own ethanol from scratch (that's super sus for a prac), but you can buy pure glucose in bottles. Glucose can also come from fruits, such as grapes (yes, wine). Some bubble tea stores use pure sucrose, which can be hydrolised to form glucose: C12H22O11(aq) + H2O(l) ---> 2C6H12O6(aq)

• If you want to find a DIY ethanol-production procedure you can just google for it.
• To determine the amount of ethanol you produce (theoretically), you can write out the balanced chemical equaiton for the fermentation of glucose into ethanol. You should know your starting mols of glucose since you're adding it yourself, and you just do a simple mol calculation to find the mols of ethanol produced. Finally, convert that to grams of whatever you want.

 

[someth1ng]

To determine the amount of ethanol you produce (theoretically), you can write out the balanced chemical equaiton for the fermentation of glucose into ethanol. You should know your starting mols of glucose since you're adding it yourself, and you just do a simple mol calculation to find the mols of ethanol produced. Finally, convert that to grams of whatever you want.

This process can have low yield so it won't give you a good estimate of ethanol content. There are analytical techniques that can determine ethanol content to ~1% like GC, HPLC, or even NMR.

 

[LennonTheLemon]

This process can have low yield so it won't give you a good estimate of ethanol content. There are analytical techniques that can determine ethanol content to ~1% like GC, HPLC, or even NMR.

True, but I'm not sure how the high school would expect you to use gas chroma. or nmr for a y12 practical...

 

[someth1ng]

True, but I'm not sure how the high school would expect you to use gas chroma. or nmr for a y12 practical...

A hydrometer to determine density will also work.

 

[Nezuko----]

Thanks for the responses so far, for the product of Ethanol (aq), would we have to use fractional distillation to separate the water and ethanol? I might be wrong, but I'm pretty sure that is the method to determine the amount of ethanol. Right?

 

[LennonTheLemon]

Thanks for the responses so far, for the product of Ethanol (aq), would we have to use fractional distillation to separate the water and ethanol? I might be wrong, but I'm pretty sure that is the method to determine the amount of ethanol. Right?

Yeah, fractional distillation is the best method you would have access to.

 

[Nezuko----]

Also, is there an estimate of how much yeast I should use? in relation to the amount of glucose I will use. Sorry for any inconvenience!!

 

[LennonTheLemon]

Also, is there an estimate of how much yeast I should use? in relation to the amount of glucose I will use. Sorry for any inconvenience!!

Not sure, google would be your best friend here, unless one of the PhD chem guys on here casually know the answer to this lol

 

[Nezuko----]

@jazz519 Would you be able to help with my question? Thanks if you could!
" Is there an estimate of how much yeast I should use? in relation to the amount of glucose, I will use." this is in relation to alcoholic fermentation practical.

 

[someth1ng]

No, you can't use fractional distillation to determine ethanol content because water and ethanol form an azeotrope and the vapour will always be a mixture of both.

An indirect method of determining ethanol content can be calculated by the mass loss from CO2 in the reaction.

As for yeast loading, something like 1 wt% should be fine. At lab scale, catalyst loading is often 1–10 mol% or wt%, depending on the reaction.