Science Buddies: "Ask an Expert"

Hello
I am currently writing my Extended Essay, in a topic where I explore how adding ligands in aqueous solution (I've been using EDTA, HCl and Ammonia) to an anode in a voltaic cell affects the electrode potential. I'm using Copper in Copper Sulfate at the moment (as a base), and then I add the various ligands to the Copper Sulfate solution and record the potential difference then.
The topic is interesting, and I am genuinely curious about the answer, but the problem is that I cannot find any explanations for why this even happens. My research online leads me to complicated articles that I have difficulties understanding, and I have researched for weeks to find something that explains it clearly enough that I can understand.
I'm usually using Google Scholar, with a search entry that is usually something like "effect of ligands on electrode potential", but I get very few relevant results.
I am desperately trying to find sources for me to use, and it is proving to be really challenging to write my first draft without knowing any of the reasons as to why this change actually happens.
I did my experiment and some of the addition of the ligands to the copper sulfate increase the potential difference measured in the voltaic cells, while some of the ligands reduce the potential difference.
Is there something I'm missing?
Could I work it out on my own?
Does anyone have any tips or places they know I can find some resources?
Or does anyone know why ligands affect the potential difference, and can, therefore, point me in the right direction by changing what I am searching for online?
Many thanks,
hamburgertheplant

Hello hamburgertheplant,

As you probably know, the potential in your voltaic cell arises from two redox half reactions involving copper and zinc. When you add EDTA, ammonia or HCl to the copper sulfate solution, some of the copper ions form a complex with the added species. Each copper complex has its own half reaction and associated potential. Thus adding the species you mentioned should result in a cell potential different from the one observed with only copper sulfate present.

Most physical chemistry textbooks have a chapter about electrochemical cells that should provide background information useful to you. A good chemical handbook (CRC handbook) should list half reactions and standard potentials for copper complexes. Also, you may want to search online for the chemical formulas to copper complexes of EDTA, ammonia and chloride.

I hope this helps. Please ask again if you have more questions.

A. Norman