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Redox Titration of an Iron Ore

Oxidation-reduction reactions can be used for quantitative analyses of both solutions and solid samples. These analyses are based on the stoichiometry of the balanced equation for the reaction. Standard solutions of known concentration are used to completely react with the unknown solution. The concentration of the standard solution and the volume used in the titration are accurately known and are used to calculate the concentration or amount of the analyte solution.

The amount of iron in ore can be quantitatively determined by titrating a solution of the unknown with a standard solution of dichromate, Cr2O72−. The net ionic equation is

6Fe2+(aq)+Cr2O72−(aq)+14H+(aq)→6Fe3+(aq)+2Cr3+(aq)+7H2O(aq)

The titration of 25.0 mL of an iron(II) solution required 18.0 mL of a 0.215M solution of dichromate to reach the equivalence point. What is the molarity of the iron(II) solution?

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Posted on September 25, 2013, in #question and tagged , , , , . Bookmark the permalink. 3 Comments.

  1. 18.0mL(.215M)=25.0mL
    3.87=25.0mL
    3.87/25.0=.1548(6:1 M ratio)= .9288M

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  2. The Fe2+(aq) solution described in Part A was produced by dissolving 4.05 g of ore in acid. What was the percentage of Fe by mass in this ore sample?

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    • moles Fe (from part A) = 0.0189

      0.0189 moles Fe x (55.85 g Fe / 1 mole Fe) = 1.06 g Fe

      %Fe = (g Fe / g ore) x 100 = (1.06 / 4.05) x 100 = 26.2% Fe

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