Analytical chemistry

an 0.5031 gram sample of iron ore is determined through redox titration using K2Cr2O7. The sample was dissolved in HCl and all the iron was converted to the 2+ state. Titration to the endpoint required 24.34 mL of 0.01887 mol/L K2Cr2O7. Calculate the amount of Fe2O3 as a percent of the original sample.

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asked by Sam
  1. Fe2O3 ==> 2Fe^3+ and reduce to Fe^2+.
    6Fe^2+ + Cr2O7^2- ==> 6Fe^3+ + 2Cr^3+
    I balanced only the redox portion of the equation which is sufficient for what we want to do.

    mols Cr2O7^2- = M x L = ?
    mols Fe = 6 x that (look at the coefficients in the equation above).
    g Fe = mols Fe x atomic mass Fe = ?

    %Fe = (g Fe/mass sample)*100 = ?

    then convert %Fe to %Fe2O3 this way.
    %Fe2O3 = %Fe x (molar mass Fe2O3/2*atomic mass Fe) = ?

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    posted by DrBob222

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