1. Determination of the Equilibrium Constant

2. Theory Beer’s Law: Concentration is proportional to Absorbance The reaction: Fe +3 + SCN - [Fe(SCN)] +2 Kc = Beer’s Law: Concentration is proportional to Absorbance The reaction: Fe +3 + SCN - [Fe(SCN)] +2 K c =

3. Fe(SCN) +2 absorbs light in the blue-green region –Set up standard curve with absorbance readings for solutions of known concentration –Beer’s Law plot

4. Math Determine moles of each reactant species Determine M for each based on total volume of solution ICE K eq = Lab,P. 298

5. Spectrophotometer 3 clean cuvettes, wipes Empty chamber –Light source on –Power knob: 0%T Water blank –447 nm –Clean cuvette with distilled water –Light source on –T knob: 100% T

6. HNO 3 blank –Set absorbance = to 0 Test solutions Zero the machine frequently http://www.chm.davidson.edu/java/spec/spec.ht mlhttp://www.chm.davidson.edu/java/spec/spec.ht ml