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Homework Help: A redox titration with kmno4- and h2o2 help

  1. Sep 18, 2015 #1
    1. The problem statement, all variables and given/known data
    Calculate the average volume of permangate ion used.

    I'm given the average volume of kmno4 used.

    2. Relevant equations

    3. The attempt at a solution

    I tried to just average my kmno4 used, but I don't believe that's what my teacher is looking for. Help?
  2. jcsd
  3. Sep 18, 2015 #2


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    You'll need to give a complete problem statement: what you're titrating, concentration of titrant, etc..
  4. Sep 18, 2015 #3

    We're titrating KMnO4 against H2O2, with some added H2SO4 so it can be a visible change.

    The KMnO4 is .025 M, and we're using various amounts.

    The H2SO4 is 6M

    I need to find the Molar Concentration of KMnO4 (I think that's the .025?) and the average volume of Permangate Ion used.

    The average amount of KMnO4 titrated against the H2O2 was 14.32 mL

    Is that enough?
  5. Sep 18, 2015 #4


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    Do you know what " 0.025 M " means?

    If you know how much permanganate ion is in 1 litre, then how much is in 14.32 ml ?

    I would guess that this is part of a series of sub-questions? If so perhaps you could show the whole question.
  6. Sep 18, 2015 #5
    Calculate the average volume of Permangate Ion used
    Calculate the moles of Permangate Ion used
    Calculate the number of moles hydrogen Peroxide titrated
    Calculate the number of grams of H2O2 titrated
    Assuming the density of the hydrogen peroxide solution to be 1.00 g/ml, calculate the percent hydrogen peroxide by mass in the solution.

    Also, thank you about the M thing. I have no clue how I missed that.
  7. Sep 18, 2015 #6


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    So you are ok with moles and molar solutions?

    If not, this is the first result I found when I Googled molar.

    You will also need to write the equation for the reaction.

    This titration is so well known and used in education, that you'll probably find the whole thing worked through on some chemistry site, if you google it.
    Last edited: Sep 18, 2015
  8. Sep 19, 2015 #7
    I don't want to google it and copy it so I can learn from this. Thanks for the site.

    I just have one quick question. When they ask for the average volume of permangate ion used, is that the average volume of all the kmno4 used during titrating, or something else?
  9. Sep 19, 2015 #8


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    I assume, since they ask you to average your volume measurements, then they want you to use this average for the remainder of the calculation.

    The alternative, to do all the calculations for each measurement, then average the results, would be much more work. I guess it would give the same result.

    Why do you think you repeat the titration and average the volumes?

    Also see Blobkins post about 3 or 4 down from yours in the forum. https://www.physicsforums.com/threads/how-to-calculate-number-of-moles-of-h2o2-oxidized.832731/
    Last edited: Sep 19, 2015
  10. Sep 20, 2015 #9
    Alright, thank you very much. I was able to finish all my questions for the actual calculations after that one hump I had issues with.

    Also; I was able to finish most of my analysis questions concerning if there was a time where someone forgot to put the acid into the flask.

    There's only one more thing I'm getting stuck on, and it's a question talking about how if there was a contaminating chemical which also reacted with hydrogen peroxide, how would it affect the percent of hydrogen peroxide.

    My gut is telling me that it would decrease the percent, because it would use it up, but I'm not 100% sure on that.
  11. Sep 20, 2015 #10


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    I'd think you're right.
    You are finding how much permanganate reacts with the peroxide. If a contaminent is reacting with some of the peroxide, then there is more peroxide than you measure with your permanganate.
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