Question

For a solution of acetophenone in hexane, the molar decadic absorptivity of the peak with λ max = 279 nm is 100 m2 mol-1

and I/I0 is 0.47. Calculate the concentration of acetophenone. Would you expect this concentration of acetophenone to change if the pathlength of light was altered from 1 cm to 3 cm, if so why

Answer 1

According to Beer-Lambert's law;

$log\dfrac{I_o}{I} =ϵlc$

$log0.47 = 100 × 1× 10^{-2} × c$

$c × 1 = log0.47$

c = 0.33 moldm^-3

This concentration of acetophenone will change if the pathlength of light was altered from 1 cm to 3 cm, because the concentration is directly proportional to the width of the cuvette (path length of light).