The published specific rotation of +-phenylsuccinic acid is +173.3 degree (Shira
ID: 529422 • Letter: T
Question
The published specific rotation of +-phenylsuccinic acid is +173.3 degree (Shiraiwa, T., Sado, Y., Fukjii, S., Nakamura, M., Kurokawo, H., Bull. Chem. Soc. Japan (1987), 60, 824-827). Our polarimeter has 1 dm cells that contain 8 mL of solution. Assume that we want to see about 10 degree of rotation. What mass of product should be dissolved in the 8 mL? Outline a procedure to make a solution of the resolved 1-phenylsuccinic acid in acetone that fits the above criteria for determination of its specific optical rotation.Explanation / Answer
Ans. Part 1: Specific rotation of a solution is given by-
[a]lT = 100a / lc - equation 1
Where,
[a]lT = specific rotation in degrees (equivalent to dm cm2 g-1)
a = observed rotation
l = cell path length in decimeter
c = concentration of solution in g/ 100mL
Putting the values in
173.30 = 100 x 100 / (1 x c)
Or, 173.30 / 10000 = 1 x c
Or, 1.733 = 1 x c
Or, c = 1.733
Therefore, concentration of the solution = 1.733 g / 100 mL
Note: Convert (if needed) all values in their respective specified units
Do not use units while doing calculation.
Concentration obtained is in terms of “g/ 100 mL” as mentioned in formula.
Since the density of solvent is 0.8 g/mL (exact value = 0.791), the 1 dm cell can hold a maximum of 8.0 mL solution.
Part 2: Given, volume of solution = 8.0 mL
Concentration of solution = 1.733 g/ 100 mL - from part 1
Now,
Mass of +-phenylsuccinic acid required = Concentration x Volume of solution
= (1.733 g/ 100 mL) x 8.0 mL
= 0.1386 g
Solution preparation: Transfer 0.1386 g of the solute to standard volumetric flask. Make the final volume upto the mark with acetone. Mix well to make a homogenous solution. It is the desired solution.
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