1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Redox Titration - Determining the % of Iron II and Iron III

  1. Feb 19, 2008 #1
    determine the % of iron II and iron III in a mixture containing both, where i am given 200cm3 of a solution containing 1.3g of iron ions(Fe 2+ Fe 3+) using potassium magnanete.
    I wrote down the equation already, and method, but i don't know how to work out the % from it :/
    Can you please help or any ideas how to start?
  2. jcsd
  3. Feb 19, 2008 #2


    User Avatar
    Homework Helper
    Education Advisor
    Gold Member

    Having the equation (which you tell us that you worked out) allows you to use stoichiometry and formula weights or formula masses and fairly simple basic mathematics arithmetic. Realize, your reaction is oxidation of the Fe+2 by Mn04-, to become Fe+3 (and whatever becomes of the permanganate).

    How many moles, and how many grams of Fe+3 did you find? From this, find how many grams of Fe+3 is in the sample.

    ... is there more to your task than you wrote in your question to the forum? Do you want ALL of the iron using a permanganate titration? I would imagine that you could use an EDTA titration to find all of the iron, and then use a permanganate titration to get the Fe+2; maybe you could first reduce the Fe+3 with some well chosen reducing agent before titrating ALL of the iron with permanganate.
  4. Feb 19, 2008 #3
    Yes thats right, well firstly I am trying to work out how much iron is present alltogether and how much of it is Iron II
    on my task sheet all it says: You have to devise a volumetric procedure to determine the percentage of iron II and Iron III in a mixture containing both.

    You are provided with 200cm3 of a solution containing between 1.1g - 1.3g of iron ions as a mixture of Fe2+ or Fe3+. You may assume that each of the 2 ions of is present to at least 30% by mass. But a balance is not avaliable.

    I know that you use titration for this to find the concentration of Iron II first, but then i confused afterwards, are we suppose to make up the concentration for Potassium Managanate?

    so we use the formulas, n= m/mr and c=nv.

    (acidified) iron (III) is reduced with granulated zinc
    2Fe3+(aq) + Zn(s) -> 2Fe2+(aq) + Zn2+(aq)

    MnO4-(aq) + 5Fe2+(aq) + 8H+(aq) " Mn2+(aq) + 5Fe3+(aq) + 4H2O(aq)
    Last edited: Feb 19, 2008
  5. Feb 19, 2008 #4


    User Avatar
    Homework Helper
    Education Advisor
    Gold Member

    This level of electrochemistry I understood many years ago, so I'll just trust that your equations are correct:
    Since it has been so long ago; are you sure that the presence of Zinc ion is not an interference with the titration with permanganate? You could use a table of electrochemical series to decide this. Any other advisers?
  6. Feb 20, 2008 #5
    I think you use Zinc to reduce it to Fe2+ in order to find out the end point from that, once you titrated completely.But im not so sure :/
    My lecturer told me to look up on that reaction on how to reduce it, so i should think it is that
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook