In a standard laboratory polarimetry experiment, an optically active compound is dissolved to yield — Isomerism and Stereochemistry Chemistry Question
Question
In a standard laboratory polarimetry experiment, an optically active compound is dissolved to yield a solution concentration of $0.02 \text{ g/mL}$. This solution is placed inside a polarimeter tube measuring exactly $10 \text{ dm}$ in length, and the observed optical rotation is recorded as $+6^\circ$. Calculate the specific rotation $[\alpha]$ of this compound in degrees.
💡 Solution & Explanation
The mathematical equation defining specific rotation is $[\alpha] = \frac{\alpha_{obs}}{l \times c}$, where $l$ is the optical path length strictly in decimeters (dm) and $c$ is the concentration in g/mL. Given $\alpha_{obs} = +6^\circ$, $l = 10 \text{ dm}$, and $c = 0.02 \text{ g/mL}$. Substituting the values: $[\alpha] = \frac{6}{10 \times 0.02} = \frac{6}{0.2} = +30^\circ$.