Kemmi Major performs an oxidation-reduction reaction in a titration. She pipets

Question

Kemmi Major performs an oxidation-reduction reaction in a titration. She pipets 20.00 mL of acidified, colorless Fe2+ solution into an Erlenmeyer flask. She places the dark purple potassium permanganate solution in the buret. The potassium permanganate concentration is 1.438 mol/L. Here is the net ionic equation for the reaction.

MnO4-(aq) + 5 Fe2+(aq) + 8 H3O+(aq) à Mn2+(aq) + 5 Fe3+(aq) + 4 H2O(l)

The initial buret reading is 2.64 mL. Kemmi titrates the potassium permanganate into the Erlenmeyer flask, and its purple color fades as the reaction occurs. When the reaction is finished the purple color remains in the solution, and so Kemmi stops the titration. The final buret reading is 14.58 mL. (Note: there is excess H3O+ present so Kemmi only needs to worry about the MnO4- and the Fe2+.)

Calculate the concentration of Fe2+in the solution. Enter the Fe2+ molarity with 4 significant digits and units of mol/L.

Explanation / Answer

Volume of potassium permanganate solution taking part in reation = final reading - initial reading = 14.58 - 2.64 = 11.94mL

Concentration = 1.438 M ;
number of moles of potassium permanganate = Conc. * Volume = 0.01194 * 1.438 = 0.01716972

From the given chemical reaction equation,
number of moles of Fe2+ = 5 * number of moles of potassium permanganate = 5 * 0.01716972 = 0.0858486

[Fe2+] = n/V = 0.0858486 * 1000 / 20 = 4.2924 M

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