> -----Original Message----- > From: [email protected] [mailto:[email protected]] > Sent: Thursday, 21 June 2001 05:08 > To: [email protected] > Subject: Re: CS>Theorizing About the Species Produced at Electrodes > During LVDC CS Pro... > > Another property of Lewis acids: > Some metal cations form Lewis acids (including silver), and the total > dissolved concentration of the metal depends upon the > concentration of the > complexing ion...say Cl-... as the concentration of Cl- increases the > concentration of Ag+ decreases (common ion effect) until a point > is reached > where Ag+ redissolves as variations of AgCl(aq) are formed eg > Ag++ Ag2Cl and > so on. > ------------------------------------------------------------------ > ------------ > > ----------------------------------------- > Ivan: I assume you are referring to several other equilibria > being setup, two > of which I've written below: > > [Ag+] + [Cl-] = AgCl(aq) > > [Ag++] + [Cl-] = AgCl2(s) > > Please tell me the likely oxidizing agent (in the blood, I guess) that > oxidized Ag+ to Ag++
There is no oxidising agent, this range of complexes is entirely due to the concentration of the ligand (the thing that is joined to the metal). > In any case, wouldn't these additional equilibria tend to remove > even more > FREE ionic silver from the bloodstream since a finite amount of > silver ions > entered the body in the first place, and these extra equilibria > will consume > additional free silver ions to form the various compounds and molecules > required by these additional equilibria? I am not really saying anything about the body, just noting the the reason for an interesting phenomenom, namely the redissolving of silver due to increasing Cl- (in this case) concentration. Rather than consuming more free Ag ions, more is actually dissolved, each complex having its own equalibrium steals Cl- from the original solubility calculation. > ------------------------------------------------------------------ > ------------ > > ------------------------------------------- > > > Quantitative Chemical Analysis 5th Ed. - Harris > has this worked example: > > What is the maximum Cl- concentration at equilibrium in a > solution in which > [2Hg2+] is somehow FIXED at 1.0E-9 M? Our concentration table looks like > this: > > Hg2Cl2(s)<===>Hg(2)2+ + 2Cl- > --------------------------------------------- > Initial concentration 0 1.0E-9 0 > Final concentration solid 1.0E-9 x > --------------------------------------------- > [Hg(2)2+] is not x in this example, so there is no reason to set > [Cl-]=2x. > The problem is solved by plugging each concentration into the solubility > product: > [Hg(2)2+][Cl-]^2 = Ksp > (1.0E-9)(x)^2 = 1.2E-18 > x = [Cl-] = 3.5E-5 M > ------------------------------------------------------------------ > ------------ > > ------------------------------------------ > Ivan: Based on your stipulation, I guess I can't disagree even > though I'm at > a loss as to how the concentration of Hg(2)2+ can remain constant WHILE > Hg2Cl2(s) is formed since, according to your scenario, this salt > wasn't there > in the first place and it will take SOME finite amount of Hg(2)2+ > to form it. I copied this straight from the book. It demonstrates how a solubility equation is handled if there is NO solid at equilibrium, and it seems to fit the manner in which silver ions are introduced into water...directly, and not as the product of salt dissolution. > ------------------------------------------------------------------ > ------------ > > -------------------------------------------- > Here is my thinking; > For every Ag+ ion released into the water an OH- ion is created > (due to the > release of H2 gas) so the [OH-] (concentration) increases at the > same rate > as the [Ag+]. > > Ivan: So far so good. > > Now if [H+] was to remain the same as found in the water That should be [OH-] > (1.0E-7) then using > the template described above (except that x is not squared > because there is > only 1 Ag+ in AgOH) the equation looks like this: > > [OH-][Ag+] = Ksp > (1.0E-7)[Ag+] = 1.52E-8 > [Ag+] = 0.152M or 16,416 mg/L > ------------------------------------------------------------------ > ------------ > > ----------------------------------------- > Ivan: If the concentration of [OH-]continues to rise so that the > product of > [OH-] and [Ag+] reaches the Ksp of AgOH near the anode then why > couldn't the > following anodic reaction occur to reduce the buildup of [OH-]? > > 4[OH-] = O2(g) + 2H2O + 4e E = Eo (-0.40) + overvoltage No, because to have water oxidised at the anode would mean the reduction of water at the cathode, the net result being zero. Without silver being oxidised and water reduced (H2 gas) there would be no net gain of Ag+. > Given enough time for OH- migration to reach the anode, isn't the > reaction > above just as likely to occur as the well known Ag+ migration to > the cathode > where it gets reduced back to silver metal? Note that this half > cell reaction > consumes 1 mole of OH per electron RELEASED just as the cathodic reaction > CONSUMES 1 electron per mole of OH- produced. Since most LVDC CS > methods I'm > aware of have a final pH around neutral, aren't these half cell reactions > sufficient to explain CS generation as well as the final pH? > > Roger As a Lewis acid a single solvated silver ion has 6 OH- ions surrounding it, which effectively frees 6 H+ ions to circulate thus lowering the pH. I have done some more calculations as above... Assuming an OH ion is generated for every Ag+ For 1E-5M of OH, the silver concentration would be 1E-5M (1ppm) but if one could add silver ions alone it could rise to 164ppm. But carrying on in this way one finds that that, as Frank noted, if one generates 1.2e-4M OH- then that is the limit before precipitation (13.5ppm). Obviously this does not happen, so what is the reason. Perhaps starting with water that is deficient in OH- ions (acidic) or the the perhaps the Lewis acid effect of silver ions has an influence. More later. -- The silver-list is a moderated forum for discussion of colloidal silver. To join or quit silver-list or silver-digest send an e-mail message to: [email protected] -or- [email protected] with the word subscribe or unsubscribe in the SUBJECT line. To post, address your message to: [email protected] Silver-list archive: http://escribe.com/health/thesilverlist/index.html List maintainer: Mike Devour <[email protected]>
