butcher said:
One thing I have noticed with some electrolytes, they will change from acidic to basic, and others just seem to become more acidic, depending on the starting solutions, sulfuric based solution seem to become more acidic and nitrate base seem to go toward hydroxide.
A little electrolytic systems 101.
Assume you are plating nickel from a standard Watts nickel plating bath using nickel anodes. This bath contains nickel sulfate, boric acid, and other things and an ideal pH for this bath is 4.3. As you apply current, nickel plates at the cathode and dissolves at the anode. Under perfect conditions, 1.095 grams (I got this number from a plating book) of nickel will dissolve per amp per hour and the same amount will plate out. Electrolytically, this number will never be higher. It is based on Faraday's laws of electrolysis and is determined by the element involved and it's valence in the particular electrolyte.
http://en.wikipedia.org/wiki/Faraday%27s_laws_of_electrolysis
When 1.095 grams of nickel per amp-hr dissolve at the anode, the anode reaction is said to be operating at 100% efficiency. The same with the plating of nickel at the cathode. At 100% efficiency of both electrodes, the system is in perfect balance and the pH will always remain at 4.3.
In practice, these dissolving and plating electrode reactions rarely operate at 100% efficiency. To utilize the entire amount of amperage applied (which must happen), other electrode reactions will occur. The exact blend of these reactions depends on many different variables. The most common of these electrode side reactions is the splitting of water. When water splits at the cathode, H2 gas escapes the solution and OH- ion enters the solution. In this case, since the OH- ion is alkaline, the pH will increase. Water splitting at the anode generates O2 gas, which escapes, and H+ ion, which enters the solution, The H+ ion is acidic and lowers the pH. The amount of water splitting at the 2 electrodes is rarely the same. Therefore, depending on many variables, the pH will usually go up or down - note that if the same amount of water splitting occurs at both electrodes, all of the H+ will combine with all of the OH-, to form water, and the pH won't change. If you use an inert anode (one that doesn't dissolve in the particular electrolyte you're using), 100% of the current applied will split water and the pH will rise. Water splitting is explained pretty well in this link.
http://www.green-planet-solar-energy.com/hydrogen-electrolysis.html
Often, there are other reactions that occur. These usually depend on the electrolyte composition and the relative affinities for various reactions to occur. For example, in solutions that contain Cl- ion, Cl2 gas will usually be generated at the anode instead of O2.
This was quite wordy and, in practice, you just need to be aware that these things can happen. It's very hard to predict exactly what will happen in a particular setup. You can only experiment and measure the results. When experimenting, consider these things I've mentioned and start out with your best guess.
Here are a few of the things that can alter the electrode reactions.
(1) The electrolyte makeup. This includes both the chemicals involved and their concentrations. Low concentrations will certainly alter the electrode reactions, especially at the cathode.
(2) The ratio of the anode surface area to the cathode surface area. In most plating applications, they recommend that the anode surface area be at least twice the cathode surface area.
(3) The temperature.
(4) In certain solutions using certain types of anodes under certain conditions, a chemical film can coat the anode. If the anode is of the soluble type, this film can impede the dissolving of the anode.
(5) The current density. This is defined as the number of amps applied per square inch (or square foot, or square decimeter, or whatever). Most electrode reactions operate most efficiently within a certain current density range.
(6) The voltage. Every metal has a certain minimum threshold voltage required in order for it to plate. The electrolyte has something to do with this also. In most cases, the voltage will be high enough so you don't have to worry about it.
This is only the tip of the iceberg.
P.S. On the silver ware or flatware I have notice silver plated on copper, and what seems to be yellow brass, but there also seems to be a white or silver colored metal they also plate to I would like to know what it is, could it just be white brass?
The white metal is usually German silver (also called nickel silver and other names), an alloy of copper and nickel that looks like silver but contains no silver.
