Monday, August 22, 2011

Question on Optical Rotation

(+)-Mandelic acid has a specific rotation of +158°. What would be the specific rotation of a mixture of 25% (+)-Mandelic acid and 75% (-)-Mandelic acid?


Answer:



If the Specific rotation of (+)-Mandelic Acid is  +158°, then the specific rotation of (-)-Mandelic Acid would be -158°. So a mixture of 25% (+)-Mandelic acid and 75% (-)-Mandelic acid should have a specific rotation of [0.25*(+158)]+[0.75*(-158)] = -79°.


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