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topic 33641

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



A discussion started in 2005 & continuing through 2017

(2005)

Q. Dear Sir/Madame:

My daughter and I are conducting a science experiment on electroplating zinc onto copper in a solution of Epsom salt, sugar and vinegar. We are using several different voltages (12,9,6, 3 and 1.5 volt batteries) to test whether higher voltages will result in faster electroplating or a heavier zinc coating on the copper.

Can you kindly shed some light on the effects of different electric voltages on the electroplating process? Will higher voltages speed up the electrolysis and electroplating process? Our one test resulted in the 12 volt battery getting very warm and then "burning out," since it apparently failed to continue producing a current. The other lower voltages did result in different levels of zinc coating, but the differences were very small.

Any comments on the role and affect of voltage on the electroplating process would be very much appreciated. Thanks in advance for your thoughtful assistance!

Alyssa and Rich

Richard Merski
- Vienna, Virginia


(2005)

A. 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 it's 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. 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 may be able to discern differences between plating rates for 1-1/2 volts and 3 volts though.

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


(2005)

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!

Rich Merski [returning]
Student - Vienna, Virginia USA


(2005)

A. As long as the copper is the cathode rather than the anode, it doesn't dissolve into solution, it simply stays metallic copper. The Zinc metal at the anode, 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+++ is beyond your daughter's age level, but that's just the way zinc ionizes in acid solutions. When those ions get to the cathode they meet up with the electrons, and are reduced back to Zn metal.

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



March 21, 2012

Q. Hey! Please I'm doing an experiment on the effect of different voltages on the rate of electroplating. Please where are the values going to be generated from, cause I'm totally confused. thanks

Vivian B. [last name deleted for privacy by Editor]
- Miami, Florida


March 21, 2012

A. Hi, Vivian. Yes, your question shows your confusion -- and I don't even know what "values" you are talking about. Sorry.

Do you very clearly, and without the least bit of confusion, understand exactly what "voltage" is? Do you very clearly, and without the least bit of confusion, understand exactly what you mean by "rate of electroplating"? A meaningful question can't be asked, and a meaningful answer provided unless the words that are used have clear, unambiguous meaning to you. You can't hope to sort out the confusion until then, so please start there.

Then make sure what you mean by "the values" and clarify it for us because I don't know what values you are referring to. Good luck.

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



July 13, 2012

Q. Hello,

I recently conducted an electrolytic plating experiment for my high school chemistry assignment, and some of the results that I obtained did not conform to the theory that the amount of metal plating is proportional to the amount of voltage that is being applied or the concentration of the electrolyte.

I plated zinc onto iron in a zinc nitrate [sic, probably meant sulfate] solution, (Zn(SO3)2 and for my particular problem, I changed the concentration of the electrolyte in three separate tests (0.5, 0.75 and 1.0 M solutions) all being powered by a 6V power pack. I did these tests twice and in both trials the 0.75 M solution resulted in the most plating. In the first trial the difference between the 0.75 M test and the 1.0 M test for the iron electrode was only 0.01 g but for the second trial is was 0.73 g. Can you please help me explain this because I don't know why this is going on?

Danny [last name deleted for privacy by Editor]
- Australia


July 16, 2012

A. Hi Danny.

Although solution concentration and 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 look up "Faraday's Law of Electrolysis", preferably in several different places, read it, 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 form 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 related due to 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 always be positively zinc ions available at the cathode to join up with the extra electrons your power pack has pumped there ... so the electrons will steel H+ from the water, converting it to H2 gas bubbles. Good luck.

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



November 10, 2015 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. I am in 7th grade, and I am doing a science fair project on electroplating. I was wondering how the concentration of salt, the voltage of the battery, and type of metal I electroplate affects the speed of electroplating.

Ramya C [last name deleted for privacy by Editor]
- Santa Clara, California, USA


November 2015

A. Hi Ramya. It's a little deep for 7th grade, but an atom of any given metal has a particular number of positively charged protons, which number we call it's "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 steal electrons from it, turning the neutral atoms into positively charged ions of the metal, which can dissolve into the plating solution.

The battery pumps those electrons from that anode metal 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 practical 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. But in the real world of practical electroplating, some concentrations might be higher than optimal and some might be lower than optimal. There are both theoretical and practical aspects of one metal vs. another that affect the plating speed, but I think that's way beyond 7th grade. Good luck.

Regards,

pic of Ted Mooney
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"


simultaneous November 11, 2015

Q. Thank you so much. So does the concentration of salt even affect the speed of electroplating? I was also wondering which metals I should test in my project. Is there any particular metal that electroplates the fastest?

Ramya C [returning]
- Santa Clara, California, USA


November 13, 2015

A. Normally, the higher the voltage, the higher the amps going to the plating. Higher amperage normally requires better solution conductivity which normally means higher salt concentration.
One kicker to this is the overvoltage potential of hydrogen and oxygen. This is the voltage at which the ions become gasses at the associated poles. This drives the efficiency way down.
Agitation is critical at higher amperages or you will get burnt plating in the high current density areas of the part.

James Watts
- Navarre, Florida


November 2015

A. Hi. The concentration of the salt does not effect the theoretical plating speed, because it 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 would depend on whether you judge by thickness or weight, and is 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,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"


September 16, 2017

Q. Hello,

I am in 9th grade, and I'm doing a science fair project on electroplating. I am testing if copper sulfate, copper nitrate, or copper chloride works best when copper plating a dime. I also want to test different voltages along with this. I could not find which 3 voltages to test. I tried searching it up, but it seems people doing the same experiment are using very different voltages. Could you please help me? Thank you!

Joy D [last name deleted for privacy by Editor]
student - Atlanta, Georgia, US


September 2017

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 6 volts (4 batteries in series).

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"


September 18, 2017

thumbs up sign Thank you so much!

Joy D [returning]
- Atlanta, Georgia US



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