Spectrophotometer Lab

Chapter 8: Spectrophotometry Question 1: a. A light including visible wavelengths of the electromagnetic spectrum also absorbs and reflects certain colors. b. The absorbance of light is critical to these molecules’ functions. Question 2: a. The spectrophotometer has an absorption spectrum that absorbs any wavelengths of light, this is why it is important to clean any finger prints or smudges before placing it in the spectrophotometer. Table 8.1 Chlorophyll 350 420 460 490 530 570 610 660

Absorbance 1.230 .880 .724 .498 .247 .214 .226 .354

Table 8.2 Acetone 10% 350 420 460 490 530 570 610 660

Question 3:

Absorbance -.018 -.006 -.008 -.009 -.007 -.006 -.007 -.007

a. 490 is the wavelength for COCl₂. b. I would except a curve of the same shape for another molecule because they are all light absorbers and reflectors. Table 8.3 Concentration of Standards 1

Absorbance -.000

10

.029

20

-.410

30

.774

40

1.120

50

1.370

Table 8.4 Unknown 1: B

1.230

Unknown 2: C

.081

Unknown 3: E

1.660

Question 4: a. The plotted points on my standard curve lie in a straight line. Question 5: a. The appropriate blank for determining the absorption of chlorophyll in a plant extract is a cuvette. b. The wavelength of 660 is least absorbed by chlorophyll. c. The wavelength of 490 is most absorbed by chlorophyll.

Table 8.5 Wavelength

Absorbance

350 420 460 490 530 570 610 660

.326 .642 1.980 1.950 1.500 .288 .003 -.002

Questions for further thought and study: 1. The absorption spectrum is the fingerprint of the chemical and is represented as a graph relating absorbance to wavelength. Standard curve is a graph showing a chemical’s concentration versus its absorbance of a wavelength of light. 2. A spectrophotometer can be used to determine the concentration of “colorless” solutes such as salt or sugar- the more solute the higher the absorbance.