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Homework Help: How to calculate initial concentration

  1. Oct 7, 2012 #1
    1. The problem statement, all variables and given/known data
    A known mass of methylamine, CH3NH2, was dissolved in water at 25 celsius

    50.0 cm^3 of this solution was taken and titrated with 1.00x10^-1 mol dm^-3 hydrochloric acid solution, HCL(aq). The change in pH as an increasing volume of hydrochloric acid was added is shown in the graph below: (Didn't scan the graph)

    2. Relevant equations
    These are the equations I think are relevant.

    3. The attempt at a solution
    I'm quite lost at what to do from here so help would be appreciated.
    Last edited: Oct 7, 2012
  2. jcsd
  3. Oct 7, 2012 #2
    Is this right? If so, I'm ashamed of meself.

    moles HCl=0.1x0.025=0.0025
    Initial concentration CH3NH2=0.0025/0.05=0.05
  4. Oct 8, 2012 #3
    your working seems correct, given that the endpoint of the titration was at 25 mL added acid. Remember that we do not have access to the unscanned pH curve for the titration.

    The other point that I would take issue with is that it would be a good idea to show a few units in your answer, and maybe even in your working.
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