Stoichiometry (College Board AP® Chemistry)

6 H⁺(aq) + 2 MnO₄⁻(aq) + 5 H₂C₂O₄ (aq) → 10 CO₂ (g) + 8 H₂O(l) + 2 Mn²⁺(aq)

A student dissolved a 0.139 g sample of oxalic acid, H₂C₂O₄ , in water in an Erlenmeyer flask. Then the student titrated the H₂C₂O₄ solution in the flask with a solution of KMnO₄ , which has a dark purple color. The balanced chemical equation for the reaction that occurred during the titration is shown above.

Identify the species that was reduced in the titration reaction. Justify your answer in terms of oxidation numbers.

The student used a 50.0 mL buret to add the KMnO₄(aq) to the H₂C₂O₄(aq) until a faint lavender color was observed in the flask, an indication that the end point of the titration had been reached. The initial and final volume readings of the solution in the buret are shown below. Write down the initial reading and the final reading and use them to determine the volume of KMnO₄(aq) that was added during the titration.

Given that the concentration of KMnO₄(aq) was 0.0235 M, calculate the number of moles of MnO₄⁻ ions that completely reacted with the H₂C₂O₄ .

The student proposes to perform another titration using a 0.139 g sample of H₂C₂O₄ , but this time using 0.00143 M KMnO₄(aq) in the buret. Would this titrant concentration be a reasonable choice to use if the student followed the same procedure and used the same equipment as before? Justify your response.