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 during the experiment were analyzed using linear regression analysis. The linear equations for each compound at the various wavelengths are provided in the table below.

Results of Linear Regression Analysis

Pathlength (cm)

	475 nm	630 nm
Compound A	y = 1.534 x	y=6.136 x	1.00
Compound B	y = 1.855 x	y =0.879 x	1.00

Using the data provided in the table above, calculate the absorbance value at 630 nm of a sample containing 0.0549M compound A and 0.00297 M compound B. Report your answer in decimal format with leading zeros. Report your answer to the correct number of significant figures.

Answer 1

Ans. Ans. In the graph, Y-axis indicates absorbance and X-axis depicts concentration. The linear regression equation in in form of “ y = mx + x”             , where-

            y = Y-axis value, depicts absorbance

            x = X-axis value, depicts concertation with respect to its absorbance

            m = slope ; (y/x) ration.

# At 630 nm:

Absorbance of A, y1 = 6.136 x                                                      ; [x = 0.0549]

Or, y1 = 6.136 x (0.0549) = 0.3369

Absorbance of B, y2 = 0.879 x                                                      ; [x = 0.00297]

Or, y2 = 0.879 x (0.00297) = 0.002611

Total absorbance of sample = Abs of molecule A + Abs of molecule B

            Or, total Abs = y1 + y2

            Or, total Abs = 0.3369 + 0.002611 = 0.3395

Hence, Abs of the sample = 0.3395