The following percent transmittances for a 0.400M chromium (III) ion solution (C

ID: 1042074 • Letter: T

Question

The following percent transmittances for a 0.400M chromium (III) ion solution (Cr3+) were recorded, using a Spectronic 20 spectrophotometer.

Wavelength (nm) Percent transmittance (%T) Absorbance (A) Wavelength (nm) Percent transmittance (%T) Absorbance (A)

700 (nm) 69.6 (%T) 575 (nm) 3.04 (%T)

675 (nm) 58.5(%T) 550 (nm) 7.09 (%T)

650 (nm) 29.0 (%T) 525 (nm) 6.92(%T)

625 (nm) 12.9 (%T) 500 (nm) 16.7 (%T)

600 (nm) 3.88 (%T) 475 (nm) 34.2 (%T)

a) (1 pts) Determine the absorbance (A) at each wavelength and fill the table, using A=2.000 - log%T.

b) (1 pts) Determine the analytical wavelength of the ion solution (?max)

Explanation / Answer

a) Prepare the following table as below.

Wavelength (nm)

A = 2 – log (%T)

700

69.6

0.157

675

58.5

0.233

650

29.0

0.538

625

12.9

0.889

600

3.88

1.411

575

3.04

1.517

550

7.09

1.149

525

6.92

1.160

500

16.7

0.777

475

34.2

0.466

b) Prepare a plot of absorbance vs wavelength as below.

The maxima of the plot gives the maximum wavelength of absorbance which is clearly at 575 nm (ans).