Question

The plot shows the absorbance spectra for solutions of caffeine, benzoic acid, and Mountain Dew® soda, each in 0.010 M HCl . A plot contains three spectra with Absorbance on the y axis and wavelength in nanometers on the x axis. Absorbance measurements range from 0.0 to 1.5, with increments every 0.2. Wavelength measurements range from 200 to 300, with icrements every 100 nanometers. A note states that All solutions contain 0.010 molar H C L. The spectrum for benzoic acid at a concentration of 8.74 milligrams per liter, begins at an absorbance of about 1.3 and 200 nanometers. Absorbance sharply decreases to 0.2 at 210 nanometers, then rises and peaks at an absorbance close to 0.8 and 228 nanometers. The spectrum for a 1 to 50 dilution of Mountain Dew soda begins at an absorbance of 1.5 and 200 nanometers, then sharply decreases in absorbance to 0.6 at 215 nanometers, then rises and peaks at absorbance close to 0.75 at 228 nanometers, decreases, then peaks again at absorbance 0.27 at 275 nanometers. The spectrum for a caffeine at a concentration of 10.88 milligrams per liter begins at an absorbance of 1.45 at 200 nanometers, then rises slightly, with a peak at absorbance 1.5 at 205 nanometers, then decreases sharply in absorbance until 0.2 at 245 nanometers. The plot then peaks again at an absorbance close to 0.6 at 270 nanometers. What is the approximate absorbance of benzoic acid at 228 nm?

Answer 1

Complete Question

The diagram of the complete question is shown on the first uploaded image.

Answer:

a) The approximate absorbance of benzoic acid at 228 nm? : A = 0.8

b) The molar absorptivity(∈)

of benzoic acid at 228 nm? : ∈   =  $1.12 * 10^{4} M^{-1} cm^{-1}$

Explanation:

Looking at the absorbance spectra, we can see that the approximate absorbance of benzoic acid at 228 is 0.8.

mass concentration of benzoic acid = $8.74 \frac{mg}{L} =8.74 * 10^{-3} \frac{g}{L}$

the molar concentration of benzoic acid = (mass concentration of benzoic acid) / (molar mass of benzoic acid )

 

molar concentration of benzoic acid = $(8.74 *10^{-3} \frac{g}{L} ) /(122.12\frac{g}{mol} )$

molar concentration of benzoic acid = $7.157 * 10^{-5}M$

molar absorptivity (∈) of benzoic acid = (absorbance) /[ (molar concentration of benzoic acid ) × (path length) ]

 

 ∈    = (0.8) / [ ($7.157 *10^{-5}M$) ×(1.00 cm)]

        =  $1.12 * 10^{4} M^{-1} cm^{-1}$