Experiment 09 · Setup Diagram
Specific Rotation
The lens L gathers the sodium lamp's light into a parallel beam. The Nicol prism P plane polarizes it, the half shade plate splits the field in two, the solution in tube T turns both planes, and the analyzer A on its graduated circle is turned until the telescope shows the halves level again. Only the angle A moved through is measured.
One half brighter than the other
Equal and faint (dull bright). Take the reading here
Equal and bright. Not the reading position
Procedure
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1.
Take 5 grams of sugar and prepare 25 cc of solution by adding water and stirring the mixture. The total volume of the solution should become 25 cc; warm the mixture if necessary. The concentration of this solution is C = 0.2 g/cc, which is 20 %.
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2.
Clean the polarimeter tube with distilled water, then fill it with water and put it between P and A.
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3.
Rotate the analyzer for uniform illumination and note this reading down as 'θ₁'.
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4.
Take care while filling the tube that no bubble is left in the light path after filling.
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5.
Now fill the tube with the sugar solution of C = 0.2 g/cc and observe θ₂. Here (θ₂ − θ₁) = θ.
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6.
Measure l, the length of the solution column, in decimetres. One decimetre is 10 cm.
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7.
Repeat the same for C = 0.1, 0.05 and 0.025 g/cc.
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8.
Plot θ on the y-axis against C on the positive x-axis. The graph is a straight line through the origin in the first quadrant. Find its slope and calculate the specific rotation from it.
slope = θ / C, S = slope / lwith l in decimetres, so the slope divided by the column length gives S