Question

To determine the concentration of individual components in a mixture of two analytes, the absorbances of the sample are measured at two wavelengths at which the difference in absorptivities of the components are large (multiple analysis). The absorbance of two compounds and their mixture at two wavelengths are given below. The optical pathlength is 2.5 cm. Concentration (ppm) | Wavelength 1 | Wavelength 2 Compound 1 | 40.0 | 0.610 | 0.400 Compound 2 | 120.0 | 0.450 | 0.600 Mixture | | 0.850 | 0.760 (a) Calculate the absorptivities of each compound at wavelengths 1 and 2. Use appropriate unit in your answers. (b) Calculate the concentration of each compound in the mixture. 

          To determine the concentration of individual components in a mixture of two analytes, the absorbances of the sample are measured at two wavelengths at which the difference in absorptivities of the components are large (multiple analysis). The absorbance of two compounds and their mixture at two wavelengths are given below. The optical pathlength is 2.5 cm.

Concentration (ppm) | Wavelength 1 | Wavelength 2
Compound 1 | 40.0 | 0.610 | 0.400
Compound 2 | 120.0 | 0.450 | 0.600
Mixture | | 0.850 | 0.760

(a) Calculate the absorptivities of each compound at wavelengths 1 and 2. Use appropriate unit in your answers.
(b) Calculate the concentration of each compound in the mixture.
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To determine the concentration of individual components in a mixture of two analytes, the absorbances of the sample are measured at two wavelengths at which the difference in absorptivities of the components are large (multiple analysis). The absorbance of two compounds and their mixture at two wavelengths are given below. The optical pathlength is 2.5 cm. Concentration (ppm) | Wavelength 1 | Wavelength 2 Compound 1 | 40.0 | 0.610 | 0.400 Compound 2 | 120.0 | 0.450 | 0.600 Mixture | | 0.850 | 0.760 (a) Calculate the absorptivities of each compound at wavelengths 1 and 2. Use appropriate unit in your answers. (b) Calculate the concentration of each compound in the mixture.

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Chemistry: Structure and Properties
Chemistry: Structure and Properties
Nivaldo Tro 2nd Edition
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To determine the concentration of individual components in a mixture of two analytes, the absorbances of the sample are measured at two wavelengths at which the difference in absorptivities of the components are large (multiple analysis). The absorbance of two compounds and their mixture at two wavelengths are given below. The optical pathlength is 2.5 cm. Concentration (ppm) | Wavelength 1 | Wavelength 2 Compound 1 | 40.0 | 0.610 | 0.400 Compound 2 | 120.0 | 0.450 | 0.600 Mixture | | 0.850 | 0.760 (a) Calculate the absorptivities of each compound at wavelengths 1 and 2. Use appropriate unit in your answers. (b) Calculate the concentration of each compound in the mixture.
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Transcript

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00:01 So there'll be quite a bit of calculating in this problem.
00:03 First, we need to calculate the absorptivities.
00:07 To do that, we'll rearrange the beerslaw equation, and absorptivity will be equal to absorbance divided by path length and concentration.
00:17 So the absorptivity for compound 1 at wavelength 1 will be equal to the absorbance at wavelength 1 for compound 1, divided by the path length, and the concentration of compound 1, 40 ppm, giving us .00611 over centimeter ppm .m.
00:38 Then the absorbent or the absorptivity for compound 1 at wavelength 2 will be the absorbance at wavelength 2 for compound 1 divided by the path length and concentration, giving us 0 .0401 over centimeter ppm, then the absorptivity for compound 2 at wavelength 1 will be equal to the absorbance for compound two at wavelength 1, divided by the path length and the concentration, 120 ppm, giving us 0 .015, 1 over centimeter ppm.
01:20 Then the absorptivity for compound 2 at wavelength 2 will be the absorbance at wavelength 2 for compound 2 divided by the path length and the concentration and we get 0 .00201 over centimeter ppm then to answer part b we're going to need two equations and two unknowns one equation will be the total absorbance will be equal to the absorptivity for compound 1 at wavelength 1 this is the total absorbance at wavelength 1 multiplied by the path length and concentration of compound one, plus compound two is also absorbing in the mixture, so it'll be the absorptivity for compound two at wavelength 1, multiplied by the path length and the concentration of compound 2.
02:21 Then at the second wavelength, we'll have the total absorbance for the two compounds in the mixture, set equal to the absorptivity for compound 1 at wavelength 2, multiplied by path length and concentration of compound 1, plus the absorptivity for compound 2 at wavelength 2, multiplied by the path length and the concentration of compound 2.
02:56 Now, if i rearrange this first equation and solve for c1, i'll multiply these together, multiply these two together, that's how i get these values.
03:11 Solve for c1, c1 is 0 .850 minus .00375 multiplied by c2, divided by 0 .01525...
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