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Homework Help: Help finding moles of pain killer/moles of hydrogen ion in a pain killer w/ titration

  1. May 13, 2008 #1
    1. The problem statement, all variables and given/known data

    Assuming the acid (pain killer) is monoprotic, calculate the moles of pain killer/hydrogen ion in a sample of an unknown pain killer using a titration:

    NaOH was added to a pain killer solution

    m[pain killer]=0.40g dissolved in 50 mL of distilled water
    [NaOH]= 0.15 mol/L
    v(NaOH)= 0.0036 L

    2. Relevant equations


    3. The attempt at a solution

    I calculated the moles of pain killer by assuming that the moles of NaOH used would be equal to the moles of pain killer used since it's a 1-1 mole ratio. I found the moles of NaOH to be 5.4 x 10^-4 mol. I could further figure out the concentration of acid solution by dividing moles by volume of distilled water but, I dont know if that would help me.

    It's really the moles of hydrogen ion that I cant get. I thought that the moles of H+ would be equal to the moles of OH in the NaOH solution which would mean that the moles of hydrogen would be equal to the moles of NaOH (since it's a strong base) but, that would mean that the moles of pain killer=moles of hydrogen ion in the pain killer which wouldn't make sense to me.

    All that said, I could really use some guidance on this as to what I've don't correctly and where I went wrong, as well as where to go from here. Thanks!
  2. jcsd
  3. May 13, 2008 #2


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    You need to distinguish between the tablet-or-capsule and the active monoprotic acid ingredient(the componant which you titrated). You are only titrating the ACID in the sample; the target acid is only a fraction of the entire sample.
  4. May 14, 2008 #3
  5. May 14, 2008 #4


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    That's the answer. Why doesn't that make sense to you? The painkiller is a monoprotic acid, yes?

    here it is again in the statement of your problem...
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