1. Spectrophotometric Determination [Co2+]
Spec 20 Lab
Spectrophotometric Determination [Co2+] 1

2. Machine that measures amount of light transmitted through a solution
Spectrophotometer
Machine that measures amount of light transmitted through a solution 2

3. Calibration of Spec 20
Setting zero
Setting 100% 3

4. Spec 20’s Zero Newer Spectrophotometer:
1. Without anything inside, press zero set button
2. Adjust left knob so scale reads exactly zero
3. Unpress zero set button
Zero Older Spectrophotometer
1. Without anything inside, adjust left knob so scale reads exactly zero 4

5. Set 100% (no color) Open door and place inside securely
Using cuvette (small test tube) of distilled water, wipe off
fingerprints with kim-wipe
Open door and place inside securely
Close door gently.
Adjust 100% knob exactly.
Remove “blank”, return to beaker.
(Do not change wavelength from 620 nm)
***Repeat each time you measure on the spectrophotometer. Use same machine for entire lab! 5

6. Your Data: Clean and dry your cuvette
Fill with M CoCl2 to level of label
Wipe fingerprints
Read % T to nearest 0.1%
Each time you change wavelength (25 nm) recalibrate!
Graph to find optimum
wavelength. 6

7. Finding optimum wavelength
Absorbance
Wavelength (nm)

8. Part 2] Beer’s Law
Follow procedure at determined wavelength to make standardized graph.

9. Part 3 Finding concentration of unknown
Since it is darkly colored, you will need to perform dilutions
Find measurement between 0.3 and 0.5
Make sure you have at least 3 mL sample
Calculations!