Attractions between Molecules

We kicked off 2018 with Lesson 42: Attraction between molecules.  Students received the Lesson 42 worksheet and then we briefly reviewed functional groups and the concept of polarity.  The lab calls for students to observe the characteristics of water, acetic acid, isopropanol, and hexane (molecular structures are shown below):

Students were tasked with writing a detailed procedure in advance of the lab tomorrow.  At the end of class, we tested the response of the four test liquids when dripped onto a piece of wax paper:

For the lab, there were four stations set up around the classroom containing all of the necessary equipment and materials to conduct the lab.  Students also could use the drawing on the white board (below) to aid in their lab setup.  Students had to follow their written procedures, which meant revising them a needed to actually complete the lab.  Results were summarized at the end of class (water, acetic acid, and isopropanol were all attracted to the charged balloon, while hexane was not).  Students realized that the acetic acid we used (36% acetic acid) contained water, as did the isopropanol (70%).  To determine whether the water in both solutions might be responsible for the attraction observed, we tested glacial acetic acid (100% acetic acid) at the end of class and found it to be highly attracted to the balloon.

Students will have the final two days of the week to write lab reports (one per group).  For the lab report (due Friday, 1/5):

  • Introduction
  • Procedure
  • Results
  • Discussion
    • Include explanation of charged balloon results
    • Include explanation of waxed paper results

On Thursday, to provide students with some foundational knowledge of polarity (helpful for making sense of the lab, and a concept we will encounter very soon in the textbook), we watched the Crash Course video below: