P507: Size counts: Building independent thinking skills through a student-centered investigation into alkali metal transport by 18-crown-6
The transition from a traditional chemistry sequence to a 1-2-1 sequence means more than a simple rearrangement of courses. The new course content in the fourth semester, as well as the increased academic maturity of the students in this course, prompted us to develop more inquiry-based experiments. The experiment presented will contain features of both open- and guided-inquiry. This experiment involves a two-week study of the transport of the alkali metals by the crown ether, 18-crown-6 (18C6) between aqueous and non-aqueous layers. During the first lab period each student determines the extent of sodium transport by 18C6, as measured spectrophotometrically. Between the first and second lab periods, students review their extraction results and propose a method to compare the relative effectiveness of 18C6 at binding and transporting each of the alkali metals (Li+, Na+, K+, Rb+, and Cs+). The proposal is expected to describe experimental procedures and controls, as well as predict the distribution ratio trend for the alkali metal series. During the second week, students carry out their proposed experiments to test their prediction. Upon completion of the experimental work, students are asked to compare their individual results with averages compiled from class data and to explain the observed trends. This experiment is also appropriate for a sophomore level organic lab when phase transfer catalysts are being discussed.