acetylmandarin

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I have a question about passage II in phase I of chapter 6 in TBR. "What does NOT make CO2 ideal for decaffeinating coffee?"

My answer to this was "B. High solubility of caffeine in CO2". In the passage, it says that CO2 is used to extract caffeine from coffee beans. Isn't extraction where you separate fluids based on their relative insolubilities? Wouldn't this mean that caffeine is insoluble in CO2 if it can be extracted from it?
The answer they chose was "A. High boiling point of CO2 at 1 atm pressure". The bp of CO2 is not given in the passage.
 

aldol16

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My answer to this was "B. High solubility of caffeine in CO2". In the passage, it says that CO2 is used to extract caffeine from coffee beans. Isn't extraction where you separate fluids based on their relative insolubilities? Wouldn't this mean that caffeine is insoluble in CO2 if it can be extracted from it?
If caffeine is very soluble in CO2, that makes CO2 very good for decaffeinating coffee because the caffeine would dissolve in the CO2 and you would be able to remove it that way. Extraction is where you take advantage of the fact that molecules are soluble in one kind of solvent but insoluble in another. A common example is aqueous and organic - your organics will go into the organic layer, leaving water-soluble compounds in the aqueous layer. So your confusion arises from where the caffeine is being extracted from. The caffeine is being extracted from the water that is your coffee. The CO2 is doing the extraction. So if caffeine is more soluble in CO2, it's going to go into the CO2 and come out when you remove the CO2, leaving you with coffee that has no caffeine.
 
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acetylmandarin

acetylmandarin

5+ Year Member
Oct 20, 2014
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If caffeine is very soluble in CO2, that makes CO2 very good for decaffeinating coffee because the caffeine would dissolve in the CO2 and you would be able to remove it that way. Extraction is where you take advantage of the fact that molecules are soluble in one kind of solvent but insoluble in another. A common example is aqueous and organic - your organics will go into the organic layer, leaving water-soluble compounds in the aqueous layer. So your confusion arises from where the caffeine is being extracted from. The caffeine is being extracted from the water that is your coffee. The CO2 is doing the extraction. So if caffeine is more soluble in CO2, it's going to go into the CO2 and come out when you remove the CO2, leaving you with coffee that has no caffeine.
Ah okay. Thanks a lot, that makes sense