What is the affect of using different voltages in the electroplating process?

A. Hi Cora. Please review our short paper on "Faraday's Law of Electrolysis" because it answers most of your question, and explains what is happening & why.

Deposition rate is directly proportional to the current (after taking 'efficiency' into account). 'Efficiency' is the percentage of the electricity which deposits metal as opposed to electrolizing the water into hydrogen and oxygen or hydroxide; the paper explains why 'efficiency' decreases at higher voltages / higher currents.

There is nothing wrong with tracking voltage vs. mass change as you are doing -- but it's tracking an indirect variable, like tracking how many pretzels you can eat before it's no longer safe to drive, if each pretzel is washed down with a swallow of beer.

It is difficult to say exactly why your efficiency dropped to zero at 5 volts, but it may be related to what is going on at the anode (the dissolving electrode) rather than the cathode. Some things that have been reported widely include 1). that nickel anodes can 'passivate' (become inactive and no longer dissolve) if the current on them gets too high; and 2). that copper anodes stop conducting current or at least greatly slow down if the amount of dissolved copper surrounding them gets too high. Although I'm not familiar with your particular case, it is certainly possible that something similar is happening to you at high voltage.

For other readers, this issue you are encountering is a good example of why it's best to track the direct variables as well as indirect ones. Someone may decide to follow an especially salty pretzel with two or three swallows of beer -- and your question would be more confidently answerable if we also knew the current flowing at 4.5 and 5 volts.

Luck & Regards,

A. Hello, Richard.
Theoretically, what controls how much plated metal is deposited is how much current (amperage) has flowed for how long (i.e., how many electrons have been transferred). This principle is known as Faraday's Law of Electrolysis if you want to do some background research. But to visualize it simply, you can think of it as: "if your battery moves the negatively charged electrons to the other pole, the positively charged metal ions will move to the other pole to catch up". At its simplest, that's how electroplating works: pull the electrons away from a metal anode, and move them to the cathode, and you are left with positively charged ions at the anode, which dissolve into the solution, migrate to the cathode, and rejoin with the electrons to become metal again.

According to another law, Ohm's Law, the amount of current flow will be proportional to the voltage: Amps = Volts/Ohms.

So, if the real world didn't rear its ugly head, the resistance would be essentially constant, and you would control the current by controlling the voltage, and your experiment would work and would prove what you'd like it to prove. However ...

Even if you were using industrial strength plating solutions, 12 volts would be too much and 9 volts might be too much because the zinc ions simply can't migrate through the solution quickly enough to keep up. So what happens then is that the excess negative and positive charges at the electrodes cause the water in the solution to break up into H+ and O--, liberating hydrogen and oxygen gas, to balance those charges. This is called inefficiency.

With the very mild acid (vinegar) that you are using, very little zinc can be held in solution; the zinc concentration is much lower than in industrial plating solutions and even 6 volts is way too much. The zinc ions in solution can't nearly keep up, so you'll get great inefficiency, substantial liberation of hydrogen, and 'burning' even at 6 volts. You might be able to discern differences between plating rates for 1-1/2 volts and 3 volts though.

Q. Dear Ted: Thank you for a very helpful and detailed response. Your answer clearly explains why our higher voltages did not work as well as the lower 1.5 or 3.0 volt tests.

One final question about coating Zinc on Copper:

What do the zinc and copper metals become in the electroplating process when charged and immersed in the Epsom salt, vinegar and sugar solution and Zinc is the anode and Copper the cathode. Does the dissolved Zinc simply become Zn- and Copper Cu+?

Thanks again for your very kind assistance!

A. As long as the copper is the cathode (negatively charged electrode) rather than the anode, it doesn't dissolve into solution, it remains metallic copper. The Zinc metal at the anode (positively charged electrode), however, has its electrons stripped from it so it becomes Zn++ (an ion with a deficit of two electrons). Why it becomes Zn++, rather than Zn+ or Zn+++ might be beyond your daughter's age level but you can read my Presentation on Faraday's Law, and see how she receives it. When those ions get to the cathode they meet up with the electrons, and are reduced back to Zn metal.

A. Hi, Vivian. Yes, your question shows your confusion -- I don't know what "values" you are talking about either; sorry!

But sorting out confusion must be done one step at a time. Do you very clearly, and without the least bit of confusion, understand exactly what "voltage" is? If not, we will start there. Do you very clearly, and without the least bit of confusion, understand exactly what you mean by "rate of electroplating"? If not, we can start there. An answer to a question usually only further confuses if you don't very clearly understand the question :-)

After we clear those two hurdles, I'll ask what you mean by "the values". Good luck.

Regards,

A. Hi Danny.

Although solution concentration & voltage can be important variables for achieving robust, attractive industrial plating, the solution concentration has nothing to do with the theoretical amount of metal that is deposited, and the voltage has only a little to do with it :-)

Please see our presentation on "Faraday's Law of Electrolysis", study it, and try your best to deeply understand it. Once you really understand it, everything will be exceptionally clear.

But, in brief, in electroplating you use a battery or power source to pump electrons from the anode to the cathode though the external copper wiring and, as you do so, you are stealing electrons from the metal of the anode which thereby converts the metal into positively charged metal ions. These ions dissolve into solution, are attracted to and migrate to the cathode, where they rejoin the electrons to become metal once again. So, the amount of metal which moves from the anode to the cathode is thus directly proportional to how many electrons you pump from the anode to the cathode, which is expressed in ampere hours (current x time).

Within reasonable limits, solution concentration has nothing to do with it, and voltage is only indirectly related per Ohm's Law that voltage equals current x resistance. But if you try to plate at too high a rate (and 6V is too high!), there will not be enough positively zinc ions available at the cathode to join up with the extra electrons your power pack has pumped there ... so the electrons will steal H+ from the water, converting it to H2 gas bubbles. Use 1.5 V for best results; 3.0 V might be workable, but 6.0 V wrecks havoc before you even start :-)   Good luck.

Regards,

A. Hi Ramya. It's probably a little deep for 7th grade, but an atom of any given metal has a particular number of positively charged protons (which we call its "atomic number"), and an equal number of negatively charged electrons balancing out the charge. If we put a piece of that metal into a watery acid solution and connect the metal to the positive pole of a battery in an electric circuit, we can pull/steal electrons from it, which turns it from neutral metal atoms into positively charged metal ions, which will dissolve into the plating solution.

The battery pumps those electrons from that anode to another piece of metal we put into the solution (called the cathode) through copper wiring. And the dissolved positively charged ions of metal are drawn to the negatively charged cathode. When they get there, they rejoin the electrons and become metal again.

Within limits, the higher the voltage, the more current will flow, so the faster the plating. From a theoretical standpoint, the concentration of salt doesn't enter into the plating speed. There are both theoretical & practical aspects of one metal vs. another that affect the plating speed, but that's probably beyond 7th grade. For 7th grade the thing to be learned might be: within practical limits, the amount of any metal moved from anode to cathode is directly proportional to the current x the time. Good luck.

Regards,

A. Hi. The concentration of the salt does not effect the theoretical plating speed, because that is calculated from Faraday's Law. But as James says, in the real world you will be able to properly plate faster at higher concentrations.

Copper or zinc would be the most practical metals to try to plate. Please see our page on "How Plating Works".

The question of what metal theoretically plates fastest may be beyond your grade level; but according to Faraday's Law again, the metal which plates fastest would be the one with the highest gram equivalent weight -- probably gold.

Regards,

A. Hi Joy. The easiest voltages to get your hands on are from 1-1/2 volt dry cell batteries. So 3 voltages worth trying are 1-1/2 volts (one battery), 3 volts (2 batteries in series), and 4-1/2 volts (3 batteries in series).

Regards,

A. Hi Khushin. Please read the article this page references about Faraday's Law of Electrolysis. Then tell us what your hypothesis will be about how voltage could effect the amount of copper electrodeposited, and we can certainly help flesh out what you would need to do to set up an experiment to support or refute that hypothesis.

However, we do need to warn you that plating copper onto steel for this experiment is probably a poor idea because copper will spontaneously deposit on steel without any electricity applied. You could account for this but it adds a layer of complexity, so your experiment might profit from switching to zinc plating on steel.

Regards,

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A. Hi Russ. There will be some amount of gassing at any voltage & current (depending on the type of electroplating solution) -- the need is to keep it within boundaries so it does not cause "burning" or other poor plating.

When this forum started in 1989, if I suggested that you forget 12V batteries and purchase a proper power supply, you could have reasonably complained that you didn't have $1000 for one :-)
But these days small, regulated, adjustable, laboratory power supplies cost less than a car battery, so please don't try to make do with something that is too high voltage, too high current, where you'll have no control, and will have to sacrifice all the other optimum plating conditions to try to work around its severe limitations. Please get a proper power supply if you want to try to learn electroplating :-)

(The word "galvanizing" is usually reserved by professionals for the process of dipping into molten zinc, so confusion will probably be minimized if you avoid that term and refer to the process as electroplating).

Luck & Regards,