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I will be given a binary mixture containing two unknown compounds(the mixture could be either liquid or solid- I don't know yet). The plan of the experiment is to identify the two compounds. So my primary concern is to separate the binary mixture and purify the individual compounds(then the subsequent classification tests/NMR/IR analysis should be straightforward). I am thinking of doing an acid-base extraction but don't know how to since I don't know any physical properties of the compounds. Any suggestions would be appreciated.

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  • $\begingroup$ I've tried to give a very general answer to your question, but it's hard to make specific suggestions without more information. Any further details you can provide will enhance the quality of responses. $\endgroup$ – Greg E. Jun 22 '14 at 0:46
  • $\begingroup$ I am doing this experiment for a OChem lab at school. Unfortunately this is all I know about the experiment(we don't even get a list of possible choices) and my instructor only allows for IR once we have done the classification tests(on the separated compounds). So I guess I will be trying random solvents. $\endgroup$ – Pepria Jun 22 '14 at 1:13
  • $\begingroup$ chromatography on silicagel in organic solvents is routinely used to separate organic compounds. It has its limitations, but its worth a shot in case nothing else pops up $\endgroup$ – permeakra Jun 22 '14 at 7:58
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N.B.: the advice below mostly applies to organic compounds. If you're dealing with inorganic salts, or solutions thereof, the approach will be very different.

For a solid mixture, I would take an IR first. That should allow you to rule out potentially useless chemical tests by identifying the functional groups present in your mixture without wasting any of the sample. This would also give you some indication whether acid/base extraction is likely to be of any use. After that, it seems logical to test solubility in a wide range of solvents and at different temperatures. If you can find one that dissolves your mixture only partially at low temperature, but completely at high temperature, then you can likely separate the components immediately by recrystallization. Judicious use of a centrifuge can help if the crystals form a fine suspension.

In the case of a liquid mixture, I would again take an IR initially. In some cases, one component of the mixture can be chemically separated, and IR results would again be useful in determining the viability of that approach. Ketones and aldehydes, for example, will react to form semicarbazones that can be recrystallized and then identified by melting point. As far as physical methods of separation, standard are distillation and fractional freezing.

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