Chemistry 2411L
Dr. Sheppard
Polarimetry Procedure
North American oil of turpentine (distilled from the oleoresin of conifer trees) primarily contains (+)-a-pinene and (-)-b-pinene. In this lab you will measure the optical rotation of a commercial turpentine to estimate the percentages of (+)-a-pinene and (-)-b-pinene it contains.
Safety:
Turpentine and its components are flammable and irritate the skin and eyes; inhalation of their vapors may be harmful. Minimize contact with the turpentine and do not breathe its vapors.
Procedure:
Measure the optical rotation of absolute ethanol using the polarimeter. Your instructor will have a polarimeter cell with absolute ethanol prepared for you to use.
Using a 25-mL volumetric flask, prepare a solution containing about 2.5 g (accurately weighed) of turpentine in absolute ethanol. Fill a 2-dm polarimeter cell with the solution. Measure the optical rotation of the solution using the polarimeter.
Prepare solutions of (+)-a-pinene and (-)-b-pinene in the same way and measure their optical rotations.
Note: If your optical rotation reading is between 0 and 89.9, report the reading as observed. If your reading is between 90.0 and 179.9, subtract 180 from the reading and report that value.
For each of the readings from the polarimeter, calculate the observed optical rotation by subtracting the reading for the solvent (absolute ethanol) from the reading for each sample.