I used titration to find the mass of iron in a $5~\mathrm{g}$ sample of spinach after leaving the spinach to soak in tap water for five different lengths of times. I added $\ce{H2SO4}$ to the solution and then titrated it with $\ce{KMnO4}$.

These are my results:

Table of Values

I found the following total reaction occurs: $$\ce{5Fe^2+ + KMnO4 + 8H+ -> Mn^2+ + 4H2O + K+ + 5Fe^3+ }$$

I am now trying to do my calculations to find my answer. I first found the amount of substance of $\ce{KMnO4}$ needed to neutralize my solution and then what I think is the initial amount of iron ($\ce{Fe^2+}$). I am stuck as I am not sure how to continue to find the actual mass of iron on the right side of the equation. Do I use stoichiometry? Is finding the $\ce{KMnO4}$ value even necessary?

  • 1
    $\begingroup$ Yes, use the stoichiometry. You have the KMnO4 concentration used, so you can calculate the iron mass. For example: If you used 0,01 mol of permanganate in the titration you have 0,05 mol of iron, this based in the stoichiometry. $\endgroup$
    – Koba
    Dec 28, 2015 at 12:27
  • 8
    $\begingroup$ Besides the question you asked, I wonder if you're getting just a reaction with iron. It seems that you were titrating a solution in which spinach leaves were soaking. There is all sorts of organic compounds in spinach that could be oxidized with permanganate. For instance spinach contains the oxalate anion. Normally for an inorganic analysis for trace metals the sample would be ashed, or the whole leaf chemically oxidized. $\endgroup$
    – MaxW
    Dec 29, 2015 at 0:34
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    $\begingroup$ As @MaxW stated above , im my experience to get the best representative sample of the iron in spinach I burnt the spinach to ash in the crucible to free the iron in the sample from the biological molecules it is bound to. This also enables the Fe+3 ions to react with the titrating reagents efficiently. HCL was then added to the ash and potassium thiocyanate was added and mixed. The red iron thiocyanate molecule was produced and the concentration was determined via spectrophotometer readings and a calibration curve previously prepared from a control solution 0.0001% Fe(SCN)3 . $\endgroup$
    – Technetium
    Dec 30, 2015 at 1:12
  • 1
    $\begingroup$ After doing more research I found that with my experiment set up I could only find the amount of ferrous oxalates in my sample of spinach. I used stoichiometry to find this value but now have to do further experiments to distinguish between the iron and the oxalate... $\endgroup$
    – SophieH
    Dec 30, 2015 at 14:05
  • $\begingroup$ Hey what are the 5 different amount of times you used?? $\endgroup$
    – Patwyn
    Jun 9, 2018 at 7:21


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