The specific rotation for a pure enantiomer is known to be +139 degrees g^-1 mL

Question

The specific rotation for a pure enantiomer is known to be +139 degrees g^-1 mL dm^-1. A sample containing both enantiomers is found to have an observed rotation of +0.87 degrees in a one dm tube at a concentration of 0.025 g/mL. What is the optical purity of the sample? What is the % of the dominant enantiomer in this sample? The specific rotation for a pure enantiomer is known to be +139 degrees g^-1 mL dm^-1. A sample containing both enantiomers is found to have an observed rotation of +0.87 degrees in a one dm tube at a concentration of 0.025 g/mL. What is the optical purity of the sample? What is the % of the dominant enantiomer in this sample?

Explanation / Answer

To know the specific rotation of sample = 0.87/0.025 = 34.8

% of Optical purity of sample = 100 * (specific rotation of sample) / (specific rotation of a pure enantiomer)
= 100 * 34.8 / 139 = 25%

% of dominant enantiomer = (100+25) / 2 = 62.5%

Hope this helps.

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