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Homework Help: CHEM Buffers

  1. Sep 26, 2010 #1
    1. The problem statement, all variables and given/known data

    You are titrating 30.0 mL of .3 M CH3NH2 with .15 M HNO3 Kb = 4.4 x 10^-4. Calculate
    pH:
    -initially
    -after 10.0 mL of acid has been added
    at the half equivalence point
    at the equivalence point
    when 70 mL of acid has been added.


    2. Relevant equations

    not sure. . .

    3. The attempt at a solution

    I was thinking that since Kb is given I can get the pOH using the fact that
    [OH] = [tex]\sqrt{K_b x Molarity}[/tex] <- im not sure if this is correct tho.

    then do an ICE table for the reaction. . . Im not sure about the reaction tho. . .

    HNO3 + CH3NH2 >> CH3NH3+ + NO3- . . .is that it?
    the first ICE table should be a limiting reagent problem?

    knowing the moles of both after 10 mL yields:

    HNO3 + CH3NH2 >> CH3NH3+ + NO3-

    .0015 | .009 ........| 0.............|0 <<<<<<<<<<Initial
    -.0015 |-.0015 .......| +.0015 .....| +.0015 <<<<<<<<Consumed
    0 ...|.0075 ..............| .0015 ......| .0015 <<<<<<< Final

    so I can get K at this point right? (K = products/reactants) but thats Ka or Kb?
     
  2. jcsd
  3. Sep 27, 2010 #2

    Borek

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    Staff: Mentor

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