An unknown solution containing a mixture of two compounds is being analyzed by U

Question

An unknown solution containing a mixture of two compounds is being analyzed by UV/visible spectrometry in order to determine the amounts of compounds A and B in the sample. Both compounds absorb to some extent at 475 and 630 nm. The calibration curve data obtained uring the experiment were analyzed using linear regression analysis. The linear equations for each compound at the various wavelengths are provided in the table below. [Pathlength (cm) Pathlength (em) Results of Linear Regression Analysis 475 nm ly 1.534 x CompoundA .00 Compound-y-1.855 x The absorbance of the unknown solution was 0.632 at 475 nm and 0.575 at 630 nm. Calculate the concentration of compound A in the unknown sample. Report your answer to 3 sigfigs using decimal notation. Use leading zeros. Do not include units.

Explanation / Answer

Given

For compound A

at 475nm

y = 1.534x

Therefore absorptivity of A at this wavelength = 1.534

at 630nm

y = 6.136x

Therefore absorptivity of A at this wavelength = 6.136

For compound B

at 475nm

y = 1.855x

Therefore absorptivity of B at this wavelength = 1.855

at 630nm

y = 0.879x

Therefore absorptivity of B at this wavelength = 0.879

Let concentration of unknown A = A1 and concentration of B = B1

Absrobance at 475nm

0.632 = Absorbance due to A + absorbance due to B

Absorbance = Concentraiton X absorptivity x path length

0.632 = A1 X 1.534 + B1 X 1.855

0.632 - 1.855 X B1 / 1.534 = A1 .......(1)

similarly at 630nm

0.575 = A1 X 6.136 + B1 X 0.879 .....(2)

Putting (1) in (2)

0.575 = 6.136(0.632 - 1.855B1) / 1.534 + 0.879 B1

0.882 = 3.878 - 11.38 B1 + 1.348 B1

2.996 = -10.032B1

B1 = 0.299

A1 = 0.632 - 1.855 X B1 / 1.534 = (0.632 - 1.855 X 0.299) / 1.534 = 0.05

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