Question

A student is doing a titration using potassium permanganate solution, KMnO4, to determine the amount of H2O2 in a sample. The balanced equation for the reaction in the titration is given below:

2 MnO4-(aq) + 6 H+(aq) + 5 H2O2(aq) -->ž 2 Mn2+(aq) + 8 H2O(l) + 5 O2(g)

A student calculates an amount of moles of H2O2 that is larger than the actual value. Which of the following errors could correctly explain the larger value?


The student failed to wear goggles.

The student did not swirl the flask appropriately and therefore stopped short of the endpoint.

The student failed to rinse the buret with KMnO4¬ solution after rinsing it with distilled water.

The student added an extra 15 mL of distilled water to the H2O2 solution.

Answer 1

Answer: The student added an extra 15 mL of distilled water to the
`H_(2)O_(2)` solution.

Explanation: As it is already mentioned that the student calculated the amount of moles of
`H_(2)O_(2)` larger than the actual value in the titration of potassium permanganate solution, the most obvious and correct answer leading to this difference is the extra amount of
`H_(2)O_(2)` used during the analysis.

The student failed to wear goggles would come under the precautions while doing an experiment in the lab.

The student did not swirl the flask appropriately and therefore stopped short of the endpoint. This reason is the hypothetical one.