Question

Now you have a chance to research into a new compound. Your job is to figure out its molar extinction coefficient. Here is experimental data:

Concentration = 12.5 ug/ml

Molecular weight = 250.0 g/ml

Cuvette pathlength = 1cm

Absorbance at 350nm = 0.55

Answer 1

Ans. Given, concentration of compound = 12.5 ug/ mL

                                                = (12.5 x 10^-6 g) / mL                       ; [1 ug = 10^-6 g]

                                                = (12.5 x 10^-6 g) / (10^-3 L)                ; [1 mL = 10^-3 L]

                                                = 1.25 x 10^-2 g / L                             ; [moles = Mass / MW]       

                                                = (1.25 x 10^-2 g / 250.0 g mol^-1) / L

                                                = (5.00 x 10^-5 mol) / L

                                                = 5.00 x 10^-5 M

Therefore, concertation of the new compound in solution = 5.00 x 10^-5 M

# Beer-Lambert’s Law, A = e C L             - equation 1             

where,

                                    A = Absorbance

                                    e = molar extinction coefficient (M^-1cm^-1)

                                    p = path length (in cm)

                                    C = concentration

Now, putting the values in equation 1 –

            0.55 = e x 5.00 x 10^-5 M x 1.0 cm

            Or, e = 0.55 / (5.00 x 10^-5 M x 1.0 cm)

            Hence, e = 1.100 x 10⁴ M^-1 cm^-1

Therefore, molar extinction coefficient of the compound, e = 1.100 x 10⁴ M^-1 cm^-1