How do I answer this?

Question

Lab Experiment: Fluoride Speciation and Analysis by Flow Injection using Ion-Selective Electrode.

Q1) what is the Nernst equation for the Fluoride Ion-Selective Electrode (ISE)? How does this show that measured potential is proportional to Fluoride ion concentration?

2Q) What is a common cause of an error when using a reference electrode?

3Q) IS the pH of solutions important when using the Fluoride ISE? If so, why?

Answer 1

Hi Kali S.,

Look like you haven't searched out for information on the web?(!) Plenty of stuff on Nernst Equation and ion-selective, even specifically for F- selective (EuF₂ doped LaF₃ as an ion conduction path) electrodes(!). The stuff on the F electrodes specifically mentions OH- as a possible interference(!). This info is not difficult to find(!). Now, that middle question -- I suspect your instructor wants you to be aware of the necessity of keeping reference electrodes properly filled with electrolyte. You want slow leakage from the reference electrode into sample solution, not the other direction! There may be other routes towards errors, which you may be alerted to be the operating instructions for the specific equipment. If you ask "Why?" a lot, you'll start receiving all the info you need. (And you won't need to keep asking Wyzant!)

--Cheers, -- Mr. d.