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Disable the effect of HCl on the PH of solution?

  1. Jun 20, 2009 #1
    well my friend is in the final year graduation and he is working on a project a part of it is trying to detect the pH of a certain compound exist in acidic HCl solution, this compund dont remember its name for recent but it has the amino 'NH2" group this compund is in solution of HCL and he wants to detect the pH of the compound containing the amino group ONLY , but the problem is that HCl would alter the pH calculation raising it..so how can he detect a ph of the amino gp located in hcl solution without the conflicting of HCl in his calculations for the amino? he was thinking about neutralizing the HCl with NaOH so that effect of HCl is cancelled but the problem is that this method sometimes is inaccurate and cause some errors..so is there any compound to be added so that it can let's say 'shield' the Hcl cancelling its effect on the ph?

    thanks in advance
  2. jcsd
  3. Jun 20, 2009 #2


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    Does your friend have a sample of the amino compound separate from the HCl ? He could study the compound separately first. He could measure pH of a few different concentrations of this compound. He could also perform a titration to obtain points for a titration curve. He would then know the pH behavior of this compound in water ( I assume water to be the exptected solvent).

    By some chance, maybe another forum member could suggest how some method in a solvent other than water might be used - but I not know, this is a stretch.
  4. Jun 20, 2009 #3


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    Performing a titration on the solution is the best way to go. From the titration curve, you will be able to figure out the pKa of the amine-containing compound, and that will allow you to predict the behavior of the compound in any aqueous solution. Any introductory chemistry textbook should have information about how you would go about calculating the pKa of a compound from a titration curve.
  5. Jun 20, 2009 #4


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    No such thing as pH of the compound, what your friend is looking for is most likely pKa or pKb (these are ways of describing acid/base dissociation constants). Follow Ygg advice.
  6. Jun 21, 2009 #5
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