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 263.5nm?

Answer 1

Lets fid the energy of both wavelength in KJ/mol

a)

when wavelength is 559.1 nm = 5.591*10^-7 m

Find energy of 1 photon first

use:

E = h*c/lambda

=(6.626*10^-34 J.s)*(3.0*10^8 m/s)/(5.591*10^-7 m)

= 3.555*10^-19 J

This is energy of 1 photon

Energy of 1 mol = energy of 1 photon * Avogadro's number

= 3.555*10^-19*6.022*10^23 J/mol

= 2.141*10^5 J/mol

= 2.141*10^2 KJ/mol

b)

when wavelength is 263.5 nm = 2.635*10^-7 m

Find energy of 1 photon first

use:

E = h*c/lambda

=(6.626*10^-34 J.s)*(3.0*10^8 m/s)/(2.635*10^-7 m)

= 7.544*10^-19 J

This is energy of 1 photon

Energy of 1 mol = energy of 1 photon * Avogadro's number

= 7.544*10^-19*6.022*10^23 J/mol

= 4.543*10^5 J/mol

= 4.543*10^2 KJ/mol

c)

energy difference = 4.543*10^2 KJ/mol - 2.141*10^2 KJ/mol

= 2.402*10^2 KJ/mol

= 240.2 KJ/mol

Answer: 240.2 KJ/mol