Organic

[elz787]

I have trouble with the "extraction" questions asked in the orgo section, anyone have any tips?

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[mikester2]

can you be more specific?

I have trouble with the "extraction" questions asked in the orgo section, anyone have any tips?

 

[elz787]

oh ya sorry, for example if a problem says you have 3 different types of compounds and it wants you to separate them out, then it gives you several choices of different extraction methods( like first add hcl, then a base, then filtration...)

 

[elz787]

also, does anyone know what physiological pH is? for example if a question says what is the net charge of a basic amino acid at physiological pH? (the answer is positive)

 

[HITMAN]

also, does anyone know what physiological pH is? for example if a question says what is the net charge of a basic amino acid at physiological pH? (the answer is positive)

Physiological pH=7.2; it refers to the typical pH of the human body, though this can vary in different organs. Sorry, I'm a little shaky myself with the extractions, but I think acids are extracted with bases, and bases with acids.

 

[dat_student]

Sorry, I'm a little shaky myself with the extractions, but I think acids are extracted with bases, and bases with acids.

not quite true. depends on the identity of your acid and/or base.

Physiological pH=7.2; it refers to the typical pH of the human body, though this can vary in different organs.

and yes physiological pH is around 7, not sure if 7.2 or 7.4 (may be a book-dependent value ). It really doesn't matter. I guess all we need to know is it's a bit higher than pH = 7

bb in 5-7 hours (hopefully)

 

[mccarth2]

That's funny, I just did that same problem today! You want to use filtration to separate the sand since it is a solid and everything else is in solution. Then you use base extraction to make the CA become a salt and more soluble in water ("like dissolves like", CA is polar and so is water) versus ether (slightly polar). Then use evaporation since ether's boiling point is lower than the CA because there is no hydrogen bonding. There is an explaination after the problem set that is probably better than how I explained it.

 

[ASU-devil]

That's funny, I just did that same problem today! You want to use filtration to separate the sand since it is a solid and everything else is in solution. Then you use base extraction to make the CA become a salt and more soluble in water ("like dissolves like", CA is polar and so is water) versus ether (slightly polar). Then use evaporation since ether's boiling point is lower than the CA because there is no hydrogen bonding. There is an explaination after the problem set that is probably better than how I explained it.

mccarth2 answered it perfectly. Just remember that when doing an extraction that if there is strong and weak solutions the weak should be used first. If the strong is used first then both the weak and the strong base/acid will be extracted at the same time.