Optical Rotation Question

[kobe200LATE]

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So I recently did an optical rotation question from berkeley review and one of the answers stated that you could decrease the optical rotation by decreasing the concentration of the enantiomer (ie if you halve the concentration of an enantiomer with optical rotation of 227 degrees then its optical rotation is 113.5 degrees).

Since I've never heard of this anywhere before, is it true that you can change the optical rotation of an enantiomer by changing its concentration? I thought the optical rotation of an enantiomer was an intrinsic property of the enantiomer itself, and not dependent on concentration.

Thanks

 

[bjb305]

this has to do with the observed rotation vs specific rotation.. pretty much, the rotation you will actually get depends on the length of the pathway of the solution and the concentration. To put it in other words, the rotation of a certain enantiomer is for a certain path length and a certain concentration. If you have a higher concentration or a longer pathway, you'll get more rotation