Hi all,
May I use the chloride ion-selective electrode with reference argentochloride electrode and Ag2S membrane suitable for an Ag(s)/AgCl(s)/KCl (aq.,sat)/Fe3+,Fe2+/(aq.)/Pt (s) system in order to construct an electochemical cell from argentochloride and Fe2+/Fe3+ electrode for determining a potential of the Fe2+/Fe3+ electrode?
When I will measure the potentials E of linear combinations of Fe2+/Fe3+ solution mixtures, I should get a linear dependence of E on ln([Fe3+]/[Fe2+]).
CN- ions do not interfere, S2- ions do, but they will not be in the solution.
Thanks,
Jan
I did not fully understand from your explanation why you need Cl-selective electrode to work with Fe2+/Fe3+ system, but I do see at least one problem in your setup: saturated KCl will be leaking from the reference electrode constantly (but uncontrollably) increasing Cl- concentration. This will be measured by Cl-selective electrode on first place. Perhaps it is better to reconsider the setup.
Cheers,
Sviatlana
I see. Generally speaking ISEs should not be used as Reference electrodes, because ISE’s potential depends on too many factors which are difficult to control and is also subject of drift.
Easiest would be to make a reference electrode, e.g. from the Cl-SE you have. Take an Eppendorf tip, fill its lower part (ca. 5mm) with 3% Agar made in saturated KCl. Then fill the rest of the tip with KCl sat. and insert there Ag/AgCl wire from your Cl-SE. Here is your brand new Ag(s)/AgCl(s)/KCl (aq.,sat) reference electrode.
Immerse it in KCl saturated overnight and its it fully ready to use.
You can also make Ag/AgCl by chlorinating Ag wire using 9V battery in ca. 1M HCl.
Cheers!
Sviatlana
Dear Jan,
It is only now that I have noticed your further question.
If you are still interested in making your own Ag/AgCl ref. electrodes, I would suggest checking out this link https://www.wpiinc.com/blog/2013/04/29/application-notes/chloriding-silver-wire/
We normally use similar procedure in our lab.
Basically you only need a 9V battery, ca. 2M HCl, and two pieces of Ag wire: one as an anode another as a cathode. It takes 1 min to plate.
Please let me know if you have any doubts,
Best wishes,
Sviatlana
As Sviatlana says, coating a silver wire with AgCl is easy!
I think you would do better if you used a double-junction electrode system, with saturated ammonium nitrate in the outer compartment. This is because the traces of chloride that will percolate through the (single) junction will complex with the Fe3+ (much more than with Fe2+) and thus affect the potential of the Fe2+/Fe3+ couple. This potential will be pH sensitive for much the same reason, but this time it will be OH- complexing with the Fe3+.
If you're using FeCl3 as the source of the Fe3+, then you wouldn't have to worry about a trace of extra Cl-, but you wouldn't have a simple Fe2+/Fe3+ equilibrium!
You can get a fair idea of what's happening in terms of Fe(III) compounds from their colour. Fe(OH2)6:3+ is pale purple (look at NH4Fe(SO4)3.12H2O solid); if your Fe(III) compound is yellow, red or colourless then you've probably got significant complexation taking place.
What you want to do sounds feasible, but make sure you understand the chemistry taking place in your solution so that you can interpret the results correctly.
David
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