Question

Let (+) tartaric acid has a specific rotation of + 11.1. Calculate the specific rotation of a mixture of 68% (+) tartaric acid and 32% (-) tartaric acid Report your answer to the closest integer.

Answer 1

Enantiomeric excess $=\frac{d-l}{d+l}\times 100=\frac{68-32}{68+32}\times 100=36\%$
$\therefore$ Optical rotation of this mixture $=\frac{36}{100}\times \left({11.1}^{\circ }\right)=4$