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Topic: How to calculate the yield in a reflux?  (Read 303 times)

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Offline MilkyWay17

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How to calculate the yield in a reflux?
« on: December 20, 2021, 03:16:06 PM »
Hello everyone, I have trouble figuring out how a reflux truly works. I understand the concept but not the exact science behind it.

Let's say I have 1 mL of a reactant, to be refluxed for 12 hours in 25 mL of acetic acid, ratio 1:25 in the synthesis, yield is 70%. The reactant solution gets dissolved into the solvent over that 12 hours, a carboxylic acid, and creates a final solution. The dissolved reactant solution fuses with a certain amount of the solvent, and the rest of the solvent that doesn't have anymore elements to combine with the reactant is later filtered, washed and dried off the new solution.

So when you read a reflux synthesis, when they say 70% yield, is it 70% yield of the reactant with the solvent total weight, or 70% yield of just the reactant itself, because even though it dissolves in the solvent, they aren't creating a new solution. And if it's just 70% yield of the reactant solution only, why does a reactant-solvent ratio matter in a reflux?

Please help me understand the science behind a reflux.

Thank you

Offline Borek

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Re: How to calculate the yield in a reflux?
« Reply #1 on: December 20, 2021, 06:26:14 PM »
Ignore reflux - you have used 1 g of ethanol and 25 g of acetic acid. Knowing the reaction equation, what theoretical yield of ethyl acetate do you expect?

If you are told the yield is 70% - what mass of the product should you collect?
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Offline MilkyWay17

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Re: How to calculate the yield in a reflux?
« Reply #2 on: December 20, 2021, 08:38:25 PM »
Thank you for replying... For the first question, I would need to know the stoichiometry of those two and I don't. Theoritical yield would be 26 grams of ethyl acetate, but actual yield will be lower depending on solubility of ethanol into acetic acid.

Second question, I don't know the answer. Solute+Solvent weight is the theoretical yield, while actual yield depends on solubility correct? So when a step in a synthesis writes 70% yield in a reflux, they mean the total weight of all mixtures? If 100 mL of solute and solvent, 70% expected yield would be 70 mL of the created solution. Correct?

Offline Borek

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Re: How to calculate the yield in a reflux?
« Reply #3 on: December 21, 2021, 03:01:04 AM »
I am afraid you are missing the most basic things about chemistry and stoichiometry, not about reflux.

None of your answers is correct. I strongly suggest you try to study basics - read some textbook, or watch some genchem101 course on youtube. At the moment to help I would need to explain everything, that's a several hours lecture. There are ready, well designed courses that will do that better than I can on the fly.
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Offline Corribus

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Re: How to calculate the yield in a reflux?
« Reply #4 on: December 23, 2021, 01:31:48 PM »
To the original question, reflux just means that any solvent lost to evaporation/boiling is  collected at the condenser and returned back to the reaction pot. I.e., it just keeps the solvent volume constant.
What men are poets who can speak of Jupiter if he were like a man, but if he is an immense spinning sphere of methane and ammonia must be silent?  - Richard P. Feynman

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