The following data are obtained for the absorbances of standard solutions of com

Question

The following data are obtained for the absorbances of standard solutions of component X, using 1.00 cm cells:

Solution            [X], molar          Absorbance

A                         0                                   0.000

B                         0.001                           0.174

C                         0.002                           0.352

D                         0.003                           0.510

E                         0.004                           0.697

A. Construct a plot of A vs. [X] and determine the calibration equation relating absorbance to [X]. Note: omit the intercept; use a regression model of the format y = mx.

B. What is the molar absorptivity? Include its units.

C.   An unknown sample is analyzed that contains X as the only absorbing species at the pertinent wavelength; A = 0.497. Calculate [X] of the unknown sample using the calibration equation.

D.   Suppose the incident light intensity was 423 arbitrary units for Standard D ( [X] = 0.003; A = 0.510). What is the transmitted light intensity for Standard D?

E. What is the % T for the unknown sample (A = 0.497)? What would the %T and A be if the same sample were analyzed using a cell with b = 2.50 cm?

Explanation / Answer

For the given data

A.plot of abs vs [X] is given below

B. Molar absorptivity = slope = (0.352 - 0.174)/(0.001)

                                               = 178 M-1.cm-1

C. For unknown with A = 0.497

[X] = 0.497/178 = 0.0028 M

D. molar absorptivity for D = 0.510/0.003 = 170 M-1.cm-1

log(Io/I) = 170 x 0.003

log(423/I) = 170 x 0.003

Transmitted ligth intensity (I) = 130.72

E. For A = 0.497

A = 2 - log(%T)

0.497 = 2 - log(%T)

%T = 31.842%

When cell of b = 2.50 cm is used,

31.842/%T = 2.5

%T = 12.737%

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