This is a continuation of the Thought Labs used as review for AP Chemistry. This style of review allows to students to incorporate the skills they have acquired throughout their course experience in AP Chemistry while providing a platform for them to increase their comfort level in situations where they are asked to apply their learning to a new lab setting. While this review is designed to be done in a small group discussion, it can be easily adapted to allow students the opportunity to work in the laboratory. In the October issue the Thought Lab was called “Lime-A-Way” (Problem 1).
AP Lab Review – Problem 2
Spend 7 – 10 minutes with your group working on the assigned lab problem. During that time you should formulate “answers” to the proposed questions and be prepared to explain and justify your answer to other groups.
Aqueous hydrogen peroxide slowly decomposes on its own into oxygen gas and water. Several materials and actions can be used to catalyze the reaction to accelerate the rate of decomposition. One such catalyst is the action of ultraviolet light on the peroxide, thus the opaque, often brown bottles, in which solutions are stored. You are given three materials that can act as catalysts for the reaction; iron(III) chloride, yeast and potassium iodide.
Materials:
- 24-well plate
- Beral pipets, microtip – 3
- Beral pipets, graduated – 3
- Spatula or scoop
- 6% hydrogen peroxide sample (50 mL)
- 1 g samples of yeast
- 1 g potassium iodide
- 1 g iron(III) chloride
- 3 small test tubes no larger than 15 mL capacity
- You have access to a balance (0.01 g), a timer, running water and paper towels.
- Thermometer
- Toothpicks - 6
- 10 mL graduated cylinder
- Distilled water (in bottle)
Questions
- Write a balanced equation for the decomposition of the hydrogen peroxide.
- Write a procedural outline for an experiment that would allow you to rank the three materials on their ability to catalyze the decomposition of the hydrogen peroxide.
- Justify the measurement portion of your procedure that would allow you to rank the catalyzing abilities of the three materials. (What would you measure and how would it help you?
- Explain
- Explain how a catalyst works.
- During your experiment you determine that the yeast is the best catalyst, followed by the potassium iodide and the iron(III) chloride. Draw an energy diagram showing the uncatalyzed reaction, and then your best guess of the catalyzed reactions, based on the fact that the enthalpy of reaction is -98.2 kJ per mole of hydrogen peroxide. For the purposes of this drawing you may assume you used a mole of hydrogen peroxide.
