Question

The optical rotaion of an optically active compound is

• A. directly proportional to the length of the polarimeter tube only
• B. directly proportional to the molar concentration of the compound
• C. independent of the length of the polarimeter tube and concentration of the compound
• D. directly proportional to both the length of the polarimeter tube and the molar concentration of the compound

Answer 1

Answer: (D)

$\alpha =\frac{\text{ observed rotation }}{\text{ length }(dm)\times \text{ concentration }}$
$\therefore$ observed rotation $=\alpha \times l\times c$
Thus, optical rotation of an optically active compound is directly proportion to both length of the polarimeter and molar concentration.