Roger, I did detail reaction (2) in my last post: reaction (2) is 2H2O ---> [2H+] + O2(g) + 4e -0.42 + -0.60 = -1.42
The over-voltage required by H and O is due to the extra energy required to rip these elements from the water (or so it has been explained to me). I think that the pH does rise somewhat, but is possible that the OH- reacts with Ag+ arriving at the cathode to form AgOH or is adsorbed to the elemental silver particles attached to the cathode, and is essentially pulled out of solution. >>>I believe this phenomenon is duplicated in reverse when, an EMF is IMPRESSED on two silver wire electrodes. Silver "ions" are produced at one electrode and hydrogen gas (at least initially) is produced at the other. Just as zinc ions are produced in one beaker WITH NO BALANCING NEGATIVE ION, silver "ions" are produced at the anode WITH NO BALANCING NEGATIVE ION because hydrogen is also released as a gas just as it occurs in the zinc/hydrogen battery example. This charge imbalance is transferred to the silver "ions", and since Frank has demonstrated that practically all electrolytic LVDC CS processes generated a mixture of ions and particles, it is likely that particulate silver combines with ionic silver and the combination of the two holds the charger in question.<<< I agree that there is no requirement for the charge of the solution to be neutral, only that the electrical laws be followed ie. that for every electron supplied at one end of the circuit one must be withdrawn at the other. I am not sure that I agree that, as in your connecting a salt bridge analogy, the charge imbalance is redressed by adding a salt. In this case the charge remains exactly the same, as you have added an essentially neutral substance, which just happens to divide into 2 equal but oppositely charged ions. The charge imbalance still remains, no matter how the ions and elements arrange themselves. By placing a salt bridge in your example you simply provide a connection which allows the charge imbalance to distribute evenly between the 2 solutions. There is no way to keep this cell running without replenishing the lost H+ ions by adding further HCl. Ivan. ----- Original Message ----- From: <[email protected]> To: <[email protected]> Sent: Monday, 2 April 2001 02:51 Subject: CS>Model to Explain Charge Buildup for LVDC CS Electrochemical Reactions > As yet, I do not have all the overvoltages corresponding to the proposed half > cell reactions given below. When I get these values (hopefully, Ivan will > come through) I may have to revise reaction (2). However, for the time being, > allow me to use the reactions below as a starting point to further explore > what happens when CS is made by the LVDC method. > > Potential Anodic Reactions > > (1) Ag -------> [Ag+] + 1e -0.80 volts (+ over voltage) > (2) 4[OH-] ---------> O2(g) + 2H2O + 4e -0.40 volts (+ over voltage) > > Potential Cathodic Reactions > > (3) 2H2O + 2e -----> H2(g) + 2[OH-] + 0.41 + 0.40 = 0.81 > (4) [Ag+] + 1e ------------> Ag(s) +0.80 (+ over voltage) > > Assuming that the over voltage for reaction (2) is such that its total > voltage is near 0.8, and taking into account that less OH- is produced per > mole of reacted water by reaction (3) than is consumed by reaction (2), the > resulting TENDENCY to consume of OH- could explain why pH values do not rise > above 7. I emphasise "tendency" because the over voltage for reaction (2) > will rise dramatically as the concentration of OH- decreases to levels based > on the ionization constant of water. > > Now let's turn our attention to how the colloidal particles are charged > during electrolysis. I believe it is instructive to examine the half cell > reactions when a zinc strip electrode is placed in one beaker of dilute HCl > and a platinized, platinum wire electrode is placed in a similar beaker which > also contains dilute HCL. Let me stipulate further that NO salt bridge > connects these two beakers. When these two electrodes are connected, there is > a driving force to oxidize zinc metal to Zn++ and to reduce H+ to H2(g). The > zinc half cell, therefore, picks up a positive charge that interferes with > the transfer of more electrons. The reduction of H+ ions in the hydrogen half > cell leads to a net negative charge as hydrogen leaves the beaker as a gas. > Both these half cell reactions will cease, or better stated, will reach > equilibrium as their total EMF is balanced by the combined charge buildup in > both half cells. > > I believe this phenomenon is duplicated in reverse when, an EMF is IMPRESSED > on two silver wire electrodes. Silver "ions" are produced at one electrode > and hydrogen gas (at least initially) is produced at the other. Just as zinc > ions are produced in one beaker WITH NO BALANCING NEGATIVE ION, silver "ions" > are produced at the anode WITH NO BALANCING NEGATIVE ION because hydrogen is > also released as a gas just as it occurs in the zinc/hydrogen battery > example. This charge imbalance is transferred to the silver "ions", and since > Frank has demonstrated that practically all electrolytic LVDC CS processes > generated a mixture of ions and particles, it is likely that particulate > silver combines with ionic silver and the combination of the two holds the > charger in question. > > Let's continue to use the zinc/hydrogen analogy by examining what happens > when a potassium chloride salt bridge IS used to connect both beakers. > Negatively charged Cl- ions flow out of one end of the "U" tube to balance > the positive charge of the Zn++ ions, and positively charged K+ ions flow out > of the other end of the tube to replace the H+ ions consumed in the other > half cell. Thus, KCL serves as a bridge to complete the electrical circuit. > Similarly, when a salt, such as NaCl is added to a LVDC CS electrolytic > process, charge buildup is diminished significantly, or even eliminated, > rendering the essentially uncharged CS product susceptible to agglomeration > and 'drop out". > > Roger > > > -- > 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]> >
