Summer Research Program for Science Teachers
Martin J. Olivieri
Academy of American Studies
Determining the Size and Purity of a Molecule Sample
Students research TLC, column, NMR procedures on software or internet. [9-12 Content Standard E- Understandings about science and technology]
I. Have the students compare the weights of two different molecules.
A. Students will follow the steps of the procedure including the set up of the equipment put out by lab specialist.
II. At the end of the experiment the students will describe how they know to what position the molecules travelled and the mathematics determining their sizes. [9-12 Content Standard B- Structure and properties of matter]
III. Students will determine the molecular mass of the molecules according to the molecular formula.
IV. The students will do a TLC of the product.
A. Explain how molecules of different sizes move up the TLC paper at different rates because they get caught in the pores of the paper. [9-12 Content Standard B- Motions and forces] The larger the molecule the slower it climbs. 30- 50% ethyl acetate: petroleum ether solution to make the solution rise through the TLC. The higher the percentage of ethyl acetate the greater the separation.
1.Count the number of substances present.
V. Set up a column according to usual procedures. Explain how the gel pores slow down the smaller molecules and allow the larger ones to pass through quickly. Teach procedures for conducting the column.
VI. After the selections giving single dots on the column TLCs are collected do an NMR to see if the samples matche the paper or approximate the expected structure.
Evaluation: Was the expected substance isolated and identified? Write a lab paper about the experiment and its findings.
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