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Homework Help: Solubility in base

  1. Mar 20, 2008 #1
    In my lab, I'm trying to identify an unknown compound. So I did a solubility test of the unknown into 5% NaOH. According to the manual it said that if it appears insoluble,take the supernatant out and add 5% HCl until neutral. If percipitate or turbidity results, it means the unknown is an acid.
    So far I thought this:
    HA (unknown) + OH- <-> H20 + A-
    I'm assuming the conjugate base was in the supernatant, but I'm not sure.
    A- + HCl <-> Cl- + HA
    I'm not sure where the percipitate or turbidity is from. Please help me!
  2. jcsd
  3. Mar 20, 2008 #2


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    In the first part, the organic acid present dissolved (why you obtained the very soluble A anion). Later, you added H+ which recombined with the A- giving you back the fairly insoluble organic acid again, the HA. The HA causes this turbidity or precipitation.
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