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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: Vodkaz on May 07, 2021, 12:43:55 PM

Title: Extract measurement
Post by: Vodkaz on May 07, 2021, 12:43:55 PM

Hello, I have a question about extraction process, I made distillation of rapeseed using petroleum ether; once finished I took some measurements of the extract's final mass directly from the round flask, no problem until then, but then I transferred the contents of the flask to a beaker and measured again; for some reason the mass was about 18 g less than before.

I'm guessing this has something to do with evaporation of the solvent after a few minutes, but is it really that quickly or what other sort of changes may happened?

Title: Re: Extract measurement
Post by: Meter on May 08, 2021, 04:55:16 AM

Evaporation might play a part, but 18 g of PE would be around 25 mL in volume (probably depends on the kind used) so it sounds like a lot if you had it all in a flask (small opening) prior and only a few minutes had passed. It could just be a measurement error. Like you forgot to tara the weight or something similar.

Title: Re: Extract measurement
Post by: Vodkaz on May 08, 2021, 05:31:56 AM

Thanks for your response, actually I do not believe that it is a tara problem (I checked the balance a few times), even though, I made the first measurement with porcelain pieces inside the flask, obviously, I left them out of the equation for measurement and it was something like this:

Mass of the extract from round flask: 93.31 g
Mass of the extract after being transferred: 77.49 g

so I am not certain at all if it is just an evaporation issue

Title: Re: Extract measurement
Post by: Meter on May 08, 2021, 05:49:07 AM

Quote from: Vodkaz on May 08, 2021, 05:31:56 AM

Thanks for your response, actually I do not believe that it is a tara problem (I checked the balance a few times), even though, I made the first measurement with porcelain pieces inside the flask, obviously, I left them out of the equation for measurement and it was something like this:

Mass of the extract from round flask: 93.31 g
Mass of the extract after being transferred: 77.49 g

so I am not certain at all if it is just an evaporation issue

Unless you live somewhere exceptionally hot, 25 mL PE is not going to evaporate out of the mouth of a flask in just a few minutes. On a large surface? Sure, but not a flask. Sounds like either a human error or a technical error with the scale. I'd repeat the extraction (being very careful to do everything right) and see if the same problem arises.

Title: Re: Extract measurement
Post by: Vodkaz on May 08, 2021, 06:23:32 AM

I agree, I'll repeat the extraction and see if the problem persists.

Thanks for your remarks