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

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

Calibration of Spec 20 Setting zero Setting 100% 3

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

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

Your Data: Clean and dry your cuvette Fill with 0.150 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

Finding optimum wavelength Absorbance Wavelength (nm)

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

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!