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    sarah1004 Posts: 107, Reputation: 1
    Junior Member

    Nov 24, 2009, 09:04 PM
    find Moles of KMnO4 used, Molarity of KMnO4 solution
    standardization of KMnO4
    Mass of H2C2O4.2H2O(MW=126g/mol),g------->0.25
    Initial buret reading, mL-------------------------->0
    Final buret reading, mL--------------------------->43
    Volume of KMnO4 solution used, mL------------>43
    Moles ofo oxalic acid used------------------------>0.002
    Moles of KMnO4 used(refer to the equation)---->??
    Molarity of KMnO4 solution------------------------>??
    2MnO4^- + 5C2O4^2- + 16H^+ ----------------> 2Mn^2+ + 10CO2 + 8H2O

    Mass of sample, g---------------------------------->0.8
    Initial buret reading, mL--------------------------->0
    Final buret reading, mL---------------------------->23
    Volume of KMnO4 used, mL----------------------->23
    Moles of KMnO4 used------------------------------>3.0
    Moles of iron in sample---------------------------->??
    Mass of iron in the sample, g---------------------->??
    Percent of iron in the sample---------------------->??
    MnO4^- + 5Fe^2+ + 8H^+ -----------------------> Mn^2+ + 5Fe^3+ + 4H2O

    I couldn't find that question marks answers.
    Please help me to find these questions...
    Thank you!
    Unknown008's Avatar
    Unknown008 Posts: 8,076, Reputation: 723
    Uber Member

    Nov 25, 2009, 10:11 AM

    1. Ok, you have the number of moles of oxalic acid used.

    You know from your equation that 5 moles of oxalic acid react with 2 moles of MnO4^-.

    Can you now guess the number of moles of MnO4^-?

    2 C2O4^2- -> 5 MnO4^-
    0.002 C2O4^2- -> ? MnO4^-

    Then, you know the number of moles of MnO4^- in 43 cm^3. Find the number of moles in 1000 cm^3.

    Is the concentration of KMnO4 130 M!

    Same thing here. You know from your equation that 5 moles of iron (II) react with one mole of MnO4^-.
    1 MnO4^- -> 5 Fe^2+
    3.0 MnO4^- -> ? Fe^2+
    [provided the concentration of MnO4^- is 130 M]

    Then, find the mass of that Fe^2+, with the AW of Fe.

    The fraction of Fe^2+ in the sample is the weight due to Fe^2+ over the total weight. The percentage is that fraction, multiplied by 100%.

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