Procedure.

You will collect data with a lab partner(s) (who should be noted in your write-up). However, all the data analysis and write-up should be done without collaboration.

You will investigate main features of the cyclic voltametry technique and measure redox potentials of three compunds. We will be using an CHI-600A meter from CH Instruments.

Learning CV and Measuring E^o

Before experiment

You should have following components available:

• Stock solutions available:
  • 5 mM Ru(bpy)₃Cl₂
  • 0.50 M KNO₃
  • 5 mM K₄Fe(CN)₆
  • 5 mM K₃Fe(CN)₆
  • 5 mM FeCl₃ in 0.25 M HCl
  • 5 mM FeCl₂ in 0.25 M HCl
• N₂ tank with reductor
• CHI ElectrochemicalAnalyzer 600A with computer
• Electrochemical Cell
• Working electrode (carbon glass)
• Reference electrode (Ag/AgCl)
• Auxilary electrode (Pt)

During experiment

• The first step is polishing and cleaning the working electrode to ensure good electron transfer. Follow advise of your TA on the appropriate technique for polishing.
• Rinse with DI water all three electrodes and assemble them onto the cell as shown.
• Attach clips to the appropriate electrodes (see picture for color coding)
• Run a voltammogram of pure electrolyte, 0.50 M KNO₃, between -0.2 and 0.9 V at 100 mV/s. Are there any signals?
• Next run a voltammogram of 1 mM Fe(CN)₆^3- in the same electrolyte and the sweep range from -0.1 to 0.5 V for different sweep rates, n = 0.5 V/s, 0.1 V/s, 0.05 V/s, 0.01 V/s, 0.005 V/s. For each case record the i_pc and i_pa as well as E_1/2 measured with the help of the program's automatic analysis software
• Next run a voltammogram of 1 mM Fe(CN)₆^4- , 1 mM Fe³⁺, and 1 mM Fe²⁺ at 0.1 V/s. Choose one of them for varying n as you did with Fe(CN)₆^3-. For the latter two use range from 0.2 to 0.9 V.
• Before you start with Ru(bpy)₃²⁺, insert a tubing with slow N₂ gas bubbling through your sample to eliminate dissolved O₂ from your solution. Let the gas run for a couple of minutes and then run a few cycles of voltammogram of pure electrolyte, 0.50 M KNO₃, between -1.6 and 2.0 V at 100 mV/s. Are there any signals? Run a few cycles of voltammogram of 5 mM Ru(bpy)₃²⁺ in the same range. You will need to be more "artistic" finding your signals. Pay attention to both anodic and cathodic currents on both sides. Are the voltammorgarms reversible? What are the E_ox and E_red of Ru(bpy)₃²⁺?
• Now try running electrolyte saturated by oxygen. For that, bubble oxygen through the sample, instead of N₂. Can you see E_1/2 for O₂ + e^- --> O₂-? Why?

After you finish

• clean up the mess after yourself
• show your notebook and the apparatus to the TA or the instructor before you leave

Tentatively, plan to run iron ions during first day, Ru(bpy)₃²⁺ and O₂ - on a second day. If you have time, you might study some other systems of your choice; it is greatly encouraged that you do so.

Last updated 02/12/02.