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Organic Chem [Napthalene and benzoic acid]

  1. Nov 19, 2009 #1
    Hi guys, i've got a question which i couldn't solve.

    Both napthalene (two benzene ring join together) and benzoic acid are aromatic compounds which exist as white solids.

    Based on their physical ahd chemical properties, describe how you could separate the components of a mixture of these two compounds without using any organic solvent.

    My only guess is to use water, since benzoic acid has the carboxylic group, but again, benzoic acid is not so soluble in water right? Any other options i could use?
     
  2. jcsd
  3. Nov 19, 2009 #2

    Borek

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    Benzoic ACID is not souble in water. What substances are soluble? Like - why NaCl is soluble?

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  4. Nov 19, 2009 #3
    NaCl is soluble because it is ionic. oh oh, can i add NaOH ? So that the benzoic dissolve in it :) ?
     
  5. Nov 19, 2009 #4

    Borek

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    That's what I would do :smile:

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  6. Nov 19, 2009 #5
    Actually, this may not quite be true. Depending on what you actually want to do, I think you can recrystallise benzoic acid from water.
     
  7. Nov 19, 2009 #6

    Borek

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    Yes, it was a little bit of exagerration on my side. Let's say weakly soluble in the cold water.

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    methods
     
  8. Nov 19, 2009 #7
    Thanks :) but then again, it is a 7 marks question. So by adding NaOH and filter and yield the acid back by adding acid. This would really give me the 7 marks would it @_@ ?
     
  9. Nov 20, 2009 #8

    Borek

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    Question asks for using chemical properties, so I think yes. But I am known to be occasionally wrong :wink:

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  10. Nov 20, 2009 #9
    Hehe thanks borek~
     
  11. Nov 20, 2009 #10

    chemisttree

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    The solubility of benzoic acid in water is:

    Temp, solubility (g/L)
    0oC, 1.7
    10oC, 2.1
    20oC, 2.9
    25oC, 3.4
    30oC, 4.2
    40oC, 6.0
    50oC, 9.5
    60oC, 12.0
    70oC, 17.7
    80oC, 27.5
    90oC, 45.5
    95oC, 68.0

    Naphthalene is entirely insoluble in water, so hot filtration could be used but since naphthalene melts at 80oC, you would have to keep it way below that temperature since it is likely to form a lower melting eutectic with benzoic acid. It is likely you wouldn't be able to use temperatures of greater than 50oC to 60oC. You would have to use a LOT of warm water!

    I think you will get your marks if you follow Borek's advice...
     
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