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Separation using acids and bases

  1. Oct 15, 2012 #1
    I am doing a lab this week where the objective is to use acids and bases and a microscale extraction to separate three solids in a mixture.

    The mixture in question is a mixture of naphthalene, benzoic acid, and ethyl 4-aminobenzoate. It will then be put through a series of solvents and extractions in order to separate the 3 components. Naphthalene is neutral, benzoic acid is acidic, and ethyl 4-aminobenzoate is basic. So if I add an acid to the mixture, the ethyl 4-aminobenzoate will separate, which I can then extract. If I then put it into another container and add NaOH, it will reform as a solid, which I can then dry with vacuum drying. Ok so there is my solid ethyl 4-aminobenzoate.

    The same can be done with a base added to separate the benzoic acid, then putting HCl to solidify the benzoic acid in another container, and dry once again. Solid Benzoic acid.

    However, I am not sure about the neutral compound. Is the idea here that I remove the benzoic acid and ethyl 4-aminobenzoate, leaving my original container only having the neutral compound, which is there by itself?

    In this process, where are the drying agents needed and how do I know how much I need?

    This is Part B of the experiment being performed later this week. The immediate Part A is to test the 5 compounds (the 3 previously mentioned compounds and the resultant compounds of adding acid (HCl)/base (NaOH), ethyl 4-aminobenzoate hydrochloride and Sodium benzoate) in 4 different solvents for solubility, and we should be able to use the results from Part A to make a ''flow scheme'' for isolating the mixture. How are the solubilities related in this case? What am I going to need to use the solubilities for to do my flow scheme?
    Last edited: Oct 15, 2012
  2. jcsd
  3. Oct 15, 2012 #2


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    Staff: Mentor


    To be honest it is not clear to me - but judging from what you wrote so far and from the selection of substances it should be enough to filter the solids and leave them to dry just in the air.

    You want to choose a solvent that has the highest solubility of the extracted substance and the lowest solubility of the other substance(s) - this way you will get the most pure substance after extraction.
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