This is some before/after

This question has probably bothered many a postgrad student - I know it bothered me during my PhD. The general question, "how long is my electrolyte stable?" is a different one from your particular case, "why is my electrolyte changing colour after a few weeks?".

The first question depends on each lab, storage conditions, and the individual making the electrolyte. It therefore varies. I was instructed by my supervisor to make new electrolyte every 2 weeks, but that was arbitrary - I judge for myself based on temperature, likelihood of contamination, and the sensitivity of my particular set of experiments.

In your case, a change of colour could be simply a change of concentration between the species - ferricyanide and ferrocyanide will balance in solution, and this equilibrium would be altered by the presence of extra KCl (and NaCl from the PBS). How sure are you that your electrolyte is at redox equilibrium, before you apply it to your cell?

Anne Sawhney

First, I want to thank you for your time.

If I understood correctly, your idea about the color change is that a redox reaction occurred in my solutions oxidizing chloride ions to make Cl2 and reducing Fe(CN)6 complex. but how is it possible to happen spontaneously when ferri/ferro cyanide cell (2mM) has a positive Ecell(0.37) and there is no chlorine gas to reduce?

furthermore, both ferri/ ferro cyanide are colored red/yellow. if there is a redox equilibrium the color shouldn't be removed or reduced.

Some of the decolored electrolytes were not even used a single time.