Question

Rose Bengal is a chromophore used in biological staining that has an absorption maximum at 559.1 nm and several other shorter wavelength absorption bands in the ultraviolet and visible regions of the spectrum when dissolved in ethanol. What is the energy difference (in kJ/mol) between the absorption maximum at 559.1 nm and a band at 221.5 nm?

Answer 1

Energy, E = hc/

Where,

H = plancks constant = 6.626 x 10^-34 J s

c = speed of light = 3.00 x 10⁸ m/s

= wavelength

Therefore,

E₁ = [(6.626 x 10^-34) x (3 x 10⁸)] /(559.1 x 10^-9) = 3.55 x 10^-19 J

E₂ = [(6.626 x 10^-34) x (3 x 10⁸)] /(221.5 x 10^-9) = 8.97 x 10^-19 J

E = E₂-E₁ = (8.97 x 10^-19 J)-(3.55 x 10^-19 J) = 5.42 x 10^-19 J/molecule

Energy difference (in kJ/mol) = Energy difference per molecule x Avogadro number

                                                = (5.42 x 10^-19 J) X 6.023 x 10²³ = 326.44 KJ/mol