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Two, atleast to me, perplexing chem problems

  1. Mar 1, 2005 #1
    1) Calculate the pH at the equivalence point in titrating 0.10 M solution of HBR with 0.08 M NaOH

    I know how to do the problem if volume amounts are included. I dont know how many liters are used and consequently the number of moles. Should I just invent some volume for one and calculate the pH based on how much the other takes to titrate it?

    2)I need to calculate the equilibrium constant for

    Ag2S + 4CL + 2H <---> 2AgCl2 + H2S

    The only information provided is Kf (what the heck is Kf?) is 1.1x10^5 for AgCl2

    How does one proceed? Thanks! :)
  2. jcsd
  3. Mar 1, 2005 #2


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    Staff: Mentor

    You may try with volumes - say - Va and Vb (for acid and base) - and do the symbolic calculations first. Volumes will cancel out at the end, as the only important thing here is the ratio of concentrations - to neutralize Va HBr solution you need 0.1/0.08*Va NaOH solution, so total volume at the end is (1+0.1/0.08)Va and so on.

    Try my BATE (see footer for link) for such calculations of pH and titration curve.

    Kf stands probably for complex formation constant. Next time write the equation with all charges, it will be much easier to understand. I wonder if it is possible to find answer without Ksp for Ag2S and Ka1, Ka2 for H2S... Ksp for AgCl s not a problem, as it is easy to remember (1e-10).

    Chemical calculators for labs and education
    BATE - pH calculations, titration curves, hydrolisis
  4. Mar 2, 2005 #3


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    Science Advisor
    Homework Helper

    You're asked for the pH. It'll be 7 at equivalence point. The equivalence point is when all of the strong acid/base has reacted with the strong base/acid. Perhaps HBr isnot considered a strong acid, then you'll need to know the Ka.

    I believe what you can do here to is to multiply the Kf by 2
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