3. Fructose, the sweetest common sugar, is sometimes sold as a dietary specialty

Question

3. Fructose, the sweetest common sugar, is sometimes sold as a dietary specialty. A sample Ith food store, is analyzed as follows: A 22.5 gram sample is dissolved in 50.0 mL of distilled and the solution is allowed to slowly equilibrate for one hour. It is then placed in a 1 dm tube in a polarimeter at 20 °C. The observed rotation is -41.4 degrees. Calculate the specific rotation. Consult the table of specific rotations for common carbohydrates and decide if the sample is pure fructose. You must show your work

Explanation / Answer

Concentration of fructose solution, c = 22.5g/50mL= 0.45 g/ml.

The observed optical rotation, [alpha] obs = -41.4 degrees

Path length, l = 1dm

Then, specific rotation = [{(alpha)obs}]/c.l = (-41.4)/0.45*1 = -92 degrees

The specific rotation of pure fructose is -87.6 degrees. So the fructose solution is not pure.

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