[McCoy]

Wuestion: Explain how you would take advantage of differences in acidity to separate and isolate the components of a mixture of benzoic acid, p-methylphenol and naphthalene (C10H8).
Can you please help me with this question by telling me what to do. All that I know is benzoic acid is more acidc than p-methylphenol which is in turn more acidic than naphthalene (C10H8).So benzoic acid will dissolves in a week base, but the rest won't.But how can I isolate each one of them?
Thank you.

[macman104]

Rank these compounds in order of decreasing acidity.  If you add a weak base, that deprotonates only the most acidic compound, how might this affect that compounds solubility in an organic solvent?  How might it affect that comopunds solubility in water?

This is a question requiring you to know about relative acidities, and then how to use these in organic/aqueous extractions.

[McCoy]

Thank you macman104 .
Well a weak base(eg NaHCO3) will react with benzoic acid,producing an ionic compound which will dissolve in water.Ionic compounds tend not to dissolve in nonpolar solvents such as diethyl ether or petrol (gasoline), so I guess the resultant compound from the reaction of benzoic acid and a weak base won't dissolve in organic solvents.Later, after getting rid of benzoic acid from the mixture(but I don't know how to separate it out), I can introduce strong base(sodium hydroxide) to dissolve the phenol(make it water soluble ionic compound) .But upto this point I'm still none the wiser..I can't figure out how to seperate each one out since  everything still remains as a mixture!
Can you please give me a bit of explanation of what to do?
Thanks.

[macman104]

Thank you macman104 .
Well a weak base(eg NaHCO3) will react with benzoic acid,producing an ionic compound which will dissolve in water.Ionic compounds tend not to dissolve in nonpolar solvents such as diethyl ether or petrol (gasoline), so I guess the resultant compound from the reaction of benzoic acid and a weak base won't dissolve in organic solvents.Later, after getting rid of benzoic acid from the mixture(but I don't know how to separate it out)

All correct so far.  The way you would separate it, is to take the aqueous layer (and remove it from the organic layer), and then reacidy it, to create the non-ionic compound again, which will then not dissolve in the water.  Then you start the process again with the other two compound.

I can introduce strong base(sodium hydroxide) to dissolve the phenol(make it water soluble ionic compound) .

Correct again, then you follow the same procedure.  Separate the organic from the aqueous, and reacidify the aqueous layer to get your non-ionic organic compound back.  Then the only thing left in the organic layer will be the naphthalene.

Nice reasoning!

[McCoy]

Thank you millions macman104, it was very kind of you to let me learnt this stuff fully.Now i think I can do other questions similar to this.There're 3 others, but you really made them easy with this explanation.
Have good one.
cheers.

[macman104]

Glad to hear up, happy to *delete me*