Question

The visible ultraviolet spectrum of a solution of concentration 9.9 x 10-5mol.L a hydroxy-1-naphthoquinone natural origin was obtained in an optical path cuvette 1 cm. In the wavelength corresponding to 330nm, the compound showed absorbance equal to 0.320. To determine the concentration of a second solution of same compound was obtained in the same conditions, a spectrum in 330nm absorbance showed equal 0.480. In the conditions under which the spectra of the samples were obtained conform to the Lambert-Beer law. The second solution, conditions of the analysis presented concentration (in mol.L-1) equal to (explain your answer.)

(A) 7.1 x 10-1. (B) 3.1 x 10-4. (C) 1.5 x 10-4. (D) 2.1 x 10-5. (E) 3.6 x 10-6.

Answer 1

Lambert-Beer law

Here,

c = 9.9 x 10^-5mol/L

l = 1 cm

A = 0.32

So,

= 0.32 /( 9.9 x 10^-5mol/L x 1cm) = 3.2  x 10³

II.

A= 0.48

  = 3.2  x 10³

l = l cm

So, using Lambert-Beer law

c = A/( x l) = 0.48 / (3.2 x 10³ x 1) = 1.5 x 10^-4

Hence, answer is C: 1.5 x 10^-4