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correct your subsequent readings.) The best technique is to approach the position of brightest
light from one side, e.g., from the positive side, and then the other side to ensure that you are
being consistent in your readings. Replace the solvent in the tube with a solution of the
compound to be measured in the same solvent. You must know the concentration of the solution
in order to calculate the specific rotation. Place the tube with the sample to be measured in the
sample chamber, following the same precautions as for the blank. View the sample through the
eyepiece and rotate the dial clockwise or counterclockwise until the same brightness as for the blank is observed. Once again, it is best to approach the final reading from both directions to
ensure consistency. Note the direction and angle of rotation from the dial. Subtract the value for
the blank, if necessary. This is the observed rotation, α, for this sample. At VCU, we are
fortunate to have a digital polarimeter at our disposal. To operate the digital polarimeter, a
student needs to insert a “blank” (polarimeter tube with solvent, only) into the chamber and push
the “reset” button. This calibrates the instrument to read zero degrees for the pure solvent.
Then, the “blank” is removed and the sample tube is inserted into the chamber. The observed...
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This note was uploaded on 03/06/2012 for the course CHEM 301 taught by Professor Sahli during the Spring '07 term at VCU.
- Spring '07