Mini-Lab 14: Molecules in Motion

This activity is designed to build a foundation for future AP Biology labs for which an understanding of molecular motion is critical. These labs include but are not limited to those involving enzyme catalysis, respiration rates, transpiration rates, and photosynthetic efficiency. The fact that this is a very inquiry based lab obviously establishes the class expectations for critical thinking and model development. Key concepts that I anticipate the student to discover include understanding the relationship between temperature and molecular speed, the relationship between concentration and diffusion rate, and what variables can affect reaction rates. While the majority of students will have completed Honors Chemistry or an Advanced Physical Science course the previous year, vocabulary that should be reinforced should be "ion", "precipitate", and "diffusion".

As this is an AP class, the majority of these students are academically in the top 20% of their class. Again, they will all have completed the prerequisite of either a year of Chemistry or an Advanced Physical Science course; they should already have competent laboratory and problem-solving skills, and should already know how to write balanced equations. They will be students primarily in 11th grade, but there will possibly be a few 10th and 12th graders as well. Irondale High School is a suburban school comprised of about 25% minority - the AP Biology class typically reflects this percentage. Students should be able to complete this lab in one 50 minute class period. Materials needed for this activity are readily available. I anticipate doing this lab as a primer for the AP required "Enzyme Catalysis Lab" which is projected to be about the 3rd week of class.

I plan to give very little direct instruction when executing this activity. Along with the lab protocol sheet, each lab station will be provided with petri dishes, ice, ruler, a heat source, mini spatulas, deionized water, and the 2 types of crystals. I will encourage but not dictate, replying to questions as Socratic as possible. The original version of the lab seems to need very few modifications; I have included those modifications in the teaching notes. Modified Lab protocol/report (Microsoft Word 83kB Aug13 08)

I plan to try to substitute the lead nitrate crystals with a suitable replacement (maybe Silver Nitrate?) that will hopefully be equally effective in forming a precipitate but not have the toxicity of lead. I will have to do some trials ahead of time.

I plan to have the student turn in the modified lab instruction sheet. It will have room between the questions for students to answer the questions right on the sheet. Depending on how long this activity actually takes when executed, it would be due either by the end of the class period or the following day. Class discussion and consensus will take place after it is corrected and turned back to them.

IIB1 - chemical kinetics
IIB2 - temperature dependence of reaction rate