Question

(ii) A sample of 2,4-hexadiene in methanol in a 2.5 cm cell shows an

absorbance of 0.65 at 240.0 nm. What is the concentration of the

diene? The molar absorption at this wavelength is 12100 dm3 mol1

cm1

.
​

Answer 1

Given,

Absorbance of the diene solution, A = 0.65

Path length of the cell, l = 2.5 cm

Molar absorptivity of the cell, ε = 12100 dm³ mol⁻¹ cm⁻¹

Let concentration of the diene be 'c'.

As per Beer-Lambert law,

A = c × ε × l

∴ Concentration of the diene, c

= $\frac{A}{ε × l}$

= $\frac{0.65}{12100 dm³ mol⁻¹ cm⁻¹ × 2.5 cm}$

= $\frac{0.65}{30250 dm³ mol⁻¹}$

= 2.14 × 10⁻⁵ dm⁻³ mol  

= 2.14 × 10⁻⁵ mol L⁻¹ [∵ 1 L = 1 dm³]