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Fe Ag reactions in used photo fix solution question.

  1. Feb 3, 2014 #1
    I had two griffin beakers with 200mL of used photo fix solution on magnetic stirrers ready for electrolysis only to find the power supply was not up to snuff.

    The backup plan was a redox reaction of Fe with Ag in solution and figure the difference of weight from the set of griffon beakers initially vs. after the reaction (dry of course). The scale had a high degree of accuracy but this otherwise crappy tool could not handle even a dry 250mL beaker. Plans changed to test tube, soon the centrifuge found its way to the table.

    A few of the recently purchased 15mL centrifuge tubes that were apparently not actually for centrifuges were loaded and then there were 2.

    I measured a whopping 2g/L...
    notice the lack of sig figs :P

    Anyway, for anyone looking for a really terrible way to measure the silver content of waste fix just follow the directions above.

    How do I improve the results while waiting on a new power supply?
    Last edited: Feb 3, 2014
  2. jcsd
  3. Feb 4, 2014 #2


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    Staff: Mentor

    If your experimental procedure is as chaotic as your description, it won't work.

    Sorry, I have troubles understanding what you did, what you plan to do, and whatnot.
  4. Feb 4, 2014 #3
    I thought what I wrote was straight forward Borek. Let's try again, this simple experiment was fraught with issues, equipment failures, and mislabeled tubes. Does that clear things up? :biggrin:

    The initial plan was to use an electrolytic cell to plate a preweighed cathode and then weigh again after the reaction was complete. From here it is simple math to calculate the amount of Ag(g)/L for our used fix solution. This did not work out because the power supply was no good with only one power leg functional at 3.9V with an amperage so low my meter wouldn't even show a reading (.002 amp setting)

    It doesn't take a rocket chemist to know this is not adequate so I moved on to ion exchange of Fe with the Ag in solution since the iron likes to give up an electron with the ionized silver in our fix solution. I am assuming this is the case because the average distance of the outermost electron to the protons is further in an average Fe atom compared to that of a silver atom and so going by Coulombs Law it should exchange an electron and result in ionized Fe with the now non ionized Silver falling from the solution.

    The magnetic stir plates were to keep the solution moving around regardless of which method was used. Yes these atoms and molecules are moving around really quickly and should be able to plate or ion exchange just fine on their own but mixing has shown to speed up my reactions in the past (even on such small samples) so they were brought into use. And they look cool to boot!

    I didn't want to take the Fe route but it was better than nothing. While I am waiting for a new power supply I figured I would run the experiment again. The centrifuge tubes were obviously an issue as well, but that will be dealt with later.

    Yes we can simply let the Silver settle out in the beakers and drain the solution from the top, rinse, repeat, etc. etc. but the centrifuge helped the Silver clump up and make for easier washing of the silver and filtering wasn't a good option because an iron oxide 'skin' formed on the top of the solutions and that would have ended up in the final weight. Siphoning from below this skin with the stirrers on seemed like the best choice.

    As stated in the original post AND again in this one, this is not an appropriate method for measuring the silver content of this used fix solution but I was using what was available at the time and taking that into consideration it was a good place to start but now it is time to improve the process.

    I am thinking about using aluminum instead of Fe for the next experiment. The hope is it will not have the same issues with an 'oxide skin' on top of the solution and so could then simply be strained, dried and weighed. Further it would be a good idea to keep the aluminum completely submerged in solution so that there is no chance for oxidation like what happened in the first experiment.

    Don't let my playful ways about the net be a reflection of how seriously I take things in the lab. My notebook is out to record data, careful measurements are taken to the highest accuracy of the equipment with the ultimate goal to attain an accurate measure of Ag(g)/L. It might not be some big fancy Polish laboratory :biggrin: but I will make it work just fine for the limited chemistry we need to perform :approve:

    In the meantime I need to go have a conversation with my local lab supply salesman about some 'centrifuge' tubes :mad:
  5. Feb 7, 2014 #4
    Well, the experiments with ion exchange were fun and all but my new power supply showed up from our campus surplus yard today. After modding it to work outside a PC it is now up and running with a stainless steel cathode happily getting deposits of silver atoms.

    I am currently running 5 volts at less than 1/2 an amp with a distance of about 20mm between the plates in a 250mL griffin beaker of our waste fix solution. This seems to be 'about' right to prevent splitting of H2O and still be able to plate.

    The cathode was weighed to (1/100) of a gram so I should be able to get a fairly accurate measure of the silver content in this solution assuming the majority of it comes out.

    Anyone have ideas on how to improve plating? Or do they usually go to completion?
    I remember in my chemistry class at the community college we measured the copper content of ore using this method (except we had some nice platinum wire anodes and cathodes) and it was surprisingly accurate compared to the other testing methods.
  6. Feb 7, 2014 #5


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    Staff: Mentor

    Sorry, I stopped reading right here: it is not even wrong. It has nothing to do with chemistry, it is some handwavy wishful thinking :mad:

    You do know what a reactivity series is? You have heard about standard redox potential? Formal potentials? Nernst equation? That's where you should start.
  7. Feb 7, 2014 #6
    Since when are chemical reactions not governed by Physics? Or am I missing a bigger picture?
    I know redox, would have to look up the rest.
  8. Feb 7, 2014 #7
    Electron transfer between two species is the basis behind the idea of redox potential that Borek mentions.
    But yes, it is a gross classical oversimplification ignoring the stability of different electron configs. entirely (from QM- blame the cat).
    try these pages:
  9. Feb 8, 2014 #8
    It is an oversimplification but start with the basics and build from there.

    It seems that current understanding places these reactions strictly in the view from a QM perspective instead of a classical one? I would have thought that moving charges were still the realm of E and M and that these objects are so complex and dynamic they are just difficult to describe so start with the simplest possible system and build from there.

    Is it wrong to delve into the EM waves emitted by these moving charges and look at how they interact with one another? Does classical mechanics break down at this point?

    I thought even a single moving electron in a magnetic field has properties that are predictable from a classical point of view, isn't this correct? Or is it that as far as our understanding today there are other 'things' at play with these types of systems and the classical view simply breaks down when looking at more complex things like these type of reactions?

    Either way, thanks for the links!

    Last edited: Feb 8, 2014
  10. Feb 8, 2014 #9
    Atomic and molecular orbital are governed by the schrodinger wave equation and in these orbitals EM waves aren't emitted (hence the electron doesn't spiral into the nucleus after loosing all energy). http://chemwiki.ucdavis.edu/Physica...anics/Atomic_Theory/Why_atoms_do_not_Collapse
    But all this is more physics and quantum chemistry rather than electrochemistry. The chemical understanding of reactions deals much more practically, (A+B->C+D+energy) the only thing about electrons that you need to know is how many are involved (ie. redox reactions) what kind of energy is released. You don't need to understand the QM behind it to do electrochemistry (thank the holey socks or I wouldn't have made past high school) or any other chemistry (...most of the time).
  11. Feb 8, 2014 #10
    I've heard about that. What I understand is we use linear differential equations to describe particles on this scale and it is the most successful description we have so far for their behavior but it does not imply they are in fact waves but just can have wave like behavour, is this right?

    What was the experiment that gave us this kind of thinking? Was it part of the Stern Gerlach experiment? (I see Schrodinger came up with this idea about the same time) Or was it theoretical and the experiment came after?

    It's nice to have a basic system to predict these things.

    I imagine that would be the case for most everyone :biggrin:
  12. Feb 8, 2014 #11
    I believe that depends on what interpretation you choose to follow.
    (stress on the believe part, I'm stretching my horizons)
    I think first was the dual nature of light (einstein's photoelectric effect) then Hisenberg's uncertainity principle then de broglie's wave-particle duality.

    We have elaborate data tables (experimental) to help us predict them, QM often is too complex to bother with and many a times results are only approximate.
  13. Feb 8, 2014 #12
    Well it at least seems to be a good description for behavior but as far as what is actually going on it seems we have no concrete idea. I looked at the equation but don't 'see' the differential equation part, do you have a derivation of it?

    Okay, looks like some further research will be needed here.
  14. Feb 8, 2014 #13


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    Staff: Mentor

    You are either joking, or trolling. Or both.

    What was the equation you looked at?
  15. Feb 8, 2014 #14
    Cheerful as always Borek :)

    this one,
    $$i\hbar {\frac {\partial }{\partial t}}\Psi ={\hat H}\Psi$$

    Is this it?
  16. Feb 8, 2014 #15


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    Staff: Mentor

    And what is [itex]\hat H[/itex]?
  17. Feb 11, 2014 #16
    That is the total energy in the system isn't it? From a classical view the total kinetic and potential, would that be the same here?
  18. Feb 11, 2014 #17


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    Staff: Mentor

    No, it is not total energy. It is an operator of total energy. Differential operator, to be more precise. It contains the "differential part" of the equation that you were not able to spot.
  19. Feb 11, 2014 #18
    Ah hah!
    Can you write it out for me
  20. Feb 11, 2014 #19


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    Staff: Mentor


    But feel encouraged to borrow/buy/download free quantum chemistry handbook and read it. There should be a chapter or two on constructing Hamiltonians.
  21. Feb 11, 2014 #20
    OMG, you are a jerk sometimes :tongue:

    You gonna loan me a book Borek? :biggrin:

    Anyway I'll look through some things, if it half way makes sense then some new threads will pop up.
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