TITLE: Optical Rotation By Sugars

AUTHOR: Marian Naveed

SCHOOL: Norwood Sr. High School

SCHOOL ADDRESS: Nichols Street, Norwood, MA 02062

For my experiment, I constructed a simple version of a scientific instrument called a Polarimeter. This instrument is used to the show the optical rotation of a substance which can help identify a substance as a dextrorotatary or a levorotatary substance. A substance is identified as a dextrorotatary substance, if the plane of polarized light is rotated clockwise. If the plane of polarized light is rotated counterclockwise, the substance is identified as levorotatary. My next step was to make saturated solutions of the three sugars-glucose, fructose and sucrose. I then took down their optical rotation, which I derived from a scale which was given. I also used different volumes and concentrations, to check to see how this would affect the substance's optical activity. By figuring out their optical rotations, I was able to identify glucose as a dextrorotatary substance and fructose as a levorotatary substance. One of the sugars however could not be identified, this was sucrose. This is because sucrose is a combination of both the glucose molecules and fructose molecules.

While testing for the compound's optical identity, I noticed that as I increased the volume of the saturated solution, the amount of optical rotation increased as well. For the third part, the higher the concentration of a solution, the more molecules of the solute (sugar) are present. Increasing the volume of a solution also increases the number of solute molecules. The fact that an increase in volume or in concentration will increase the amount of rotation suggests that the amount of optical rotation is directly proportional to the number of sugar molecules encountered by the light.