Question

The plot shows the absorbance spectra for solutions of caffeine, benzoic acid, and Mountain Dew soda, each in 0.010 M HCI. All solutions contain 0,010 M HCI What is the approximate absorbance of benzoic acid at 228 nm? Benzoic acid 8,74 mg/L Absorbance Mountain Dew soda 1:50 dilution Caffeine 10,88 mg/L A What is the molar absorptivity (C) of benzoic acid at 228 nm? Assume that the path length is 1.00 cm. 0.21 0.0- 200 M'cm-1 220 240 260 280 Wavelength (nm) 300

Answer 1

The absorbance of benzoic acid at 228 nm is 0.8

We can find absorptivity (e) using formula Absobance = e x C x l  

where C is concentration = 8.74 mg/L = 0.00874 g/L , we need in moles / L ,  

Benzoic acid in moles / L = ( mass /L) / ( molar mass of benzoic acid) = ( 0.00874 g/L / 122g/mol) = 0.0000716 mol/L

= 0.0000716 M

now substituting all in formula we get 0.8 = e x 0.0000716 M x 1 cm

e = 11173 M-1cm-1