Hydrogen peroxide solution slowly decomposes into water and oxygen gas
CHEMISTRY · Multi-part · AP · Chemistry · Chemical Reactions · Chemical Reactions
Problem
Hydrogen peroxide solution slowly decomposes into water and oxygen gas. To study this process, a student places 25 mL of 3.0 % (by mass) H₂O₂(aq) in an Erlenmeyer flask along with a small quantity of MnO₂ powder, which acts as a catalyst. The flask is fitted with a balloon that initially contains only air at atmospheric pressure and is held tightly around the neck of the flask. The entire apparatus is allowed to stand undisturbed at 22 °C for one hour.
(1) Describe TWO independent macroscopic observations the student should make during the hour that provide evidence the decomposition reaction is occurring.
(2) For EACH observation listed in part (a), articulate a corresponding particulate-level description that accounts for the macroscopic evidence.
(3) Suppose the student removes the balloon, leaves the flask open to the atmosphere, and continues to observe for another hour. Predict how the mass of the flask and its contents after the additional hour will compare with the mass recorded just before the balloon was removed. Provide a chemical explanation for your prediction.
(4) Catalysts are not consumed in a reaction. Propose ONE experimental test the student could perform at the end of the study to confirm that the MnO₂ powder has not undergone a chemical change, and explain the expected result if the catalyst remained chemically unchanged.