Determination of the Equilibrium Constant

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# Determination of the Equilibrium Constant - PowerPoint PPT Presentation

Determination of the Equilibrium Constant. 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 = .

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### Determination of the Equilibrium Constant

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
• Kc =
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
Math
• Determine moles of each reactant species
• Determine M for each based on total volume of solution
• ICE
• Keq =
• Lab,P. 298
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
HNO3 blank
• Set absorbance = to 0
• Test solutions
• Zero the machine frequently
• http://www.chm.davidson.edu/java/spec/spec.html