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topic 28434

Electroplating copper from copper sulfate bath for science project

Current question and answers:

December 2, 2020

Q. Hello,

My son wants to validate the atomic mass unit of copper through a copper electroplating experiment. Passing a known amount of current for a given time (ampere-seconds) and measuring the mass of copper deposited, and then using the principle behind Faraday's law, he wants to calculate what he finds the atomic mass unit of copper to be :-) experimentally and check whether it is indeed 63.5. He is estimating that if he can get 3 gms of copper deposited through passing a current of 1.25 Amps for 6 hours (using a low-cost DC power supply), he may be able to get some calculations he can work with. We already have a scale that can measure to 0.01g so he may plan to do 2-3 trials.

I am writing to you since it is unclear how much electrolyte he should use and what would be best way for him to measure the amount of copper deposited. He was planning to use an iron electrode (4 inch long bar, 12g) and a copper electrode (4 inch long bar, 12 g) from a science experiment tools store.

Thank you in advance for your guidance!

Kiran

Kiran Kuntamukkala
- San Jose, California




December 2020

A. Hi Kiran, that's an ambitious science project! I didn't carefully check your numbers, but they look about 2X too high. Remember that in acid copper sulphate, the oxidation state/valence of the copper is +2, which means you need to move 2 electrons through the power supply and wiring, not 1, for each ion of copper you want to transfer from anode to cathode through the solution.

But don't use an iron cathode because copper, being more noble than iron, will spontaneously deposit a thin layer on it without electricity, slightly changing the data. I would suggest just using two copper electrodes and carefully measuring the weight of both, and the weight of the solution before and after the experiment (if the solution & beaker aren't too heavy for your scale), which will offer checks and balances against measurement errors. In the unlikely event that the total of the three changes, he'll have another thing to consider & report -- that some of the weight might have evaporated as water or turned to hydrogen and floated off :-)

I don't know the surface area of those 4 inch long bars, and you probably only want to submerge 3 to 3-1/2 inches in the solution, because you won't want the connection submerged in the solution and possibly corrupting the situation. But I wouldn't suggest trying to plate at more than about 10 amps/square foot, so I think the 1.25 Amps is probably high. Shooting for less copper deposited or plating for 12 hours might be better.

A beaker of 300-500 mL would be ideal because he can also record and track the solution level, to see if some was lost to evaporation or hydrogen. I'd get the beaker first and see how much solution corresponds to a 3 to 3-1/2" level (but obviously less than 300-500 mL).

With the before & after weight of the anode, the before & after weight of the cathode, the before & after weight of the solution, the ampere-hours of electricity, and the before & after solution level he should have outstanding data for his terrific experiment.

Luck & Regards,

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Ted Mooney, P.E. RET
finishing.com - Pine Beach, New Jersey
Aloha -- an idea worth spreading


December 6, 2020

Q. Hello, Mr. Mooney,

Thank you so much for your terrific guidance on my son's project. He is very grateful. I have ordered the DC supply, glass beaker set with various sizes, and copper electrodes for him. I have a few follow-up questions.

1. For making the electrolyte, is it ok to buy copper sulfate crystals or powder and mixing with water? or is it better to buy pre-made copper sulfate electrolyte. If it is the former, then how many gms would be best to order.

2. Based on 10 amps/sq.foot recommendation, my son converted this guidance to amp/sq.inch and for plating both sides of roughly 3 sq.inch of his electrode, he is thinking 0.5 Amps. He will run this for a longer time (12 hours). I got him a couple extra electrodes in case his first run doesn't work out ;-)

3. Can you pls validate if our understanding of the scientific principle is correct: When electricity is passed, the copper cations Cu2+ from the copper sulfate solution will go to the copper cathode and deposit as metallic copper, while the sulfate anions (SO4) 2- will go to copper anode and combine with the copper and leach out more CuSO4 back into the electrolyte (replenishing the copper ions). This process keeps going on as electricity is passed. We will lose some electrolyte as you mentioned to evaporation. Is our understanding correct?

4. So for his calculations: the total mass of copper deposited will be increase in weight of the copper cathode. I'm wondering how does the decrease in weight of copper anode and any changes to the electrolyte factor in his calculations for mass of copper deposited.

Thank you so very much for your continued guidance!

Kiran Kuntamukkala [returning]
- San Jose California


December 2020

A. Hi again Kiran. I have never actually done the experiment, but:

1. When people talk about buying or using copper sulphate, they usually actually mean Copper sulphate pentahydrate, CuSO4·5H20. This is the blue crystals or powders you generally see. It is quite soluble, so he should be able to readily dissolve it in water. The advantage of using crystals or powder over buying a liquid is that you'll know how much actual copper sulphate you have, whereas if you buy a liquid then you'll have to trust the percentage from the label to know how much copper sulphate you have versus water.
A standard copper plating bath is about 210 grams per liter but you can operate at much lower concentration, and you may not be able to dissolve quite that much anyway, so buying 100 grams for a 300-500 mL beaker should be more than enough. You're also supposed to have about 30 grams per liter of sulfuric acid in your plating bath, but you didn't tell us how old your son is so I don't know if that's appropriate. You may want to just use vinegar instead. In that case, I'd probably use about 1 part vinegar to 4 parts water (200 grams per liter).

2. 0.5 Amp sounds okay to me.

3. Your understanding is correct, but you don't really even have to worry about the sulphate to understand it: when your power supply strips two electrons from the anode and pushes them through the copper wiring to the cathode, what used to be an atom of Cu0 on the anode has now been turned into a Cu+2 ion in solution. It will migrate over to the cathode where it re-meets those 2 electrons and becomes an atom of copper again.

4. The anode weight and solution weight don't factor into his calculation for the weight gain at the cathode; that's a free-standing measurement; sorry for confusing/misleading you ...
But, just as one atom of copper should deposit on the cathode for each 2 electrons transferred, one atom of copper should be removed from the anode. So the weight loss from the anode should match the weight gain on the cathode -- just a built-in check.
My suggestion about weighing the solution and watching for evaporation was probably overkill, I only mentioned it because if the weight gain of the cathode doesn't match the weight loss from the anode, the only explanation is that there is either more or less copper dissolved in the solution at the end of the test than at the beginning; probably just skip that and weigh the anode and cathode before and after rather than going nuts with data :-)

Luck & Regards,

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Ted Mooney, P.E. RET
finishing.com - Pine Beach, New Jersey
Aloha -- an idea worth spreading


December 7, 2020

A. Please do not forget the 2 most important ingredients of the experiment: safety glasses and gloves.

Leon Gusak
- Winnipeg, Canada


December 8, 2020

thumbs up sign Thank you Mr. Mooney so very much for such detailed guidance!

I think my son now has ample clarity to embark on his experiment.

Per Leon's advice, I will be sure to ensure he keeps his safety gloves and glasses at all times ;-)

Kiran Kuntamukkala [returning]
- San Jose, California




Previous closely related Q&A's starting in:

2004

Q. Hello,

I am a freshman student in an honors chemistry class. I have conducted an electroplating experiment that tested the effect of different amounts of copper sulfate [affil. link to info/product on Amazon] in the bath(g) on the change in mass of a nickel from before it was plated to after it was plated with copper. I had 100 trials total. The four amounts of copper sulfate tested were 5 g, 10 g, 15 g, and 20 g dissolved in 150 mL of water. From the results I gathered my data showed that there is virtually no difference in how much copper was plated on the nickel despite the different amounts that were used. I am now writing my lab report and my teacher wants me to find out why there was no difference between in the change of the mass of the nickels. My experiment obviously showed that the amount of copper sulfate in the plating bath has no effect on how much the nickel is plated but I really need to know why.

I am sorry if this is a stupid question, but I am not very familiar with this site and do not know if it has already been answered elsewhere, and I don't have a lot of time. I appreciate any help you can give me. Thank you and please respond as soon as you can.                                 

Melissa A [last name deleted for privacy by Editor]
student - Columbia, Missouri, United States


2004

A. Not a stupid question at all, Melissa. You are very industrious to plate 100 samples, good for you, and your results are exactly correct! Here is what happens--

The copper ions are sitting in solution, doing essentially nothing until you apply electricity. Then, when you apply electricity and a copper ion is touching your nickel cathode, two electrons flow into it reducing it from a Cu++ ion to a Cu0 metal atom. So the amount of copper deposited is proportional to the number of electrons that flowed, i.e., the coulombs or ampere-seconds, NOT the copper concentration. This is Faraday's Law, and we're very happy you demonstrated it so well.

There is, however, a second reaction that occurs to a much lesser degree. Those two electrons can sometimes instead be wasted in the liberation of hydrogen from water,
2H2O + 2e => H2 + 2OH.

If 100 percent of your electricity goes into depositing copper, the process is said to be operating at 100 percent efficiency. If 10 percent of the electricity goes into liberating hydrogen from water, the process is operating at 90 percent efficiency. At high copper concentrations and reasonable current, like you used, copper plating is close to 100 percent efficient because it is much easier to reduce copper than hydrogen; but if you lower the copper concentration way down, the efficiency will drop off. You can understand this by remembering that I started by saying "a copper ion is touching your nickel cathode". Suppose that the concentration is so low that at a given instant no copper ions are near or touching the cathode? The electricity still needs to flow, and will do so by liberating hydrogen from the water.

You did a great experiment and demonstrated Faraday's Law -- with the great 'control' of showing that copper concentration within reasonable limits has no effect on plating rate! (but had you run another trial with a greatly reduced copper concentration, you might have seen the reduced efficiency that results from too little copper in solution).

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
finishing.com - Pine Beach, New Jersey
Striving to live Aloha



February 1, 2009

Q. I am helping my 7th grade child with a science project that involves ECD of copper using different concentrations of copper sulfate solution. At higher concentrations it went pretty well and he observed nicely deposited copper formations. At successively lower concentrations there seemed to be increased bubbling (presumably electrolysis of water?) but also the deposits were black. Is this an optical property of the deposited copper, CuO or something else?

Thanks,
Dan

Dan Abraham
hobbyist - Northport, New York, US


February 1, 2009

A. Hi, Dan. The black deposit you are seeing is called "burning" or "smut", and I can tell you basically what it is, but it's hard to put a fine point on it in terms of percentages, because it is the result of a process that is out of control and therefore erratic and unpredictable. One component of it is a very finely deposited copper powder (if powders are fine enough they tend to look black because the tiny balls bounce light away at skew angles instead of reflecting it back.

It is caused, as previously mentioned, by trying to plate at a higher voltage/current than the solution can sustain. The electricity must take two paths to complete the circuit, electrons flow through the copper wire, while positively charged copper ions flow through the solution. If there isn't enough copper in the solution to sustain the current you are passing through the wire, the instant a copper ion reaches the cathode it is instantly reduced to a spec of powder instead of slowly growing a proper grain structure. Additionally, water is hydrolyzed into hydrogen and oxygen to try to carry the current.

It is possible to successfully plate copper with a low concentration of copper in the solution, but you must plate at a lower voltage and consequently slower so the small concentration of copper ions is sufficient to match the electrons you are passing through the wire. Good luck.

Regards,

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
finishing.com - Pine Beach, New Jersey
Striving to live Aloha



March 16, 2010

Q. My name is Aditi and I'm doing a chemistry project on Electrolysis. I'm in the ninth grade. I'm plating a steel rod with copper from a CuSO4 solution. I want to know what reactions take place and whether the SO4 ions will rush to the other electrode.

Aditi L.
Student - Pune, Maharashtra, India


October 2013

A. Hi Aditi. Sorry, but your experiment will not be successful because electroplating copper onto a steel rod is a problem. Copper is more noble than steel, so copper will deposit onto the rod without any electricity applied. As for the reaction involved, the copper sulphate ionizes into Cu++ and SO4- -, and the Cu++ ions migrate over to the steel surface. When they reach it, they "steal" electrons from the steel because they are more noble than the steel is. Thus the copper ions become neutralized and deposit as copper metal onto the rod, while simultaneously the iron (steel) atoms lose their electrons and ionize into solution. When the steel surface is completely covered with copper metal, the reaction will stop.

However, if you apply electricity at that point, you can make it continue. You'll pump electrons to the cathode, where they will continue to reduce Cu++ ions to copper metal, and the electrons you pulled from the anode will cause the copper atoms of the anode to dissolve into solution as Cu++ ions.

Regards,

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Ted Mooney, P.E.
finishing.com - Pine Beach, New Jersey
Striving to live Aloha



Need very heavy copper plating on top of nickel plating

January 10, 2019

Q. Dear sir. I run a small electronics company (mostly power electronics) and we need to have a thick copper plate applied to a nickel plated spring clip and a nickel (or gold) plated magnet. The cladding must be a minimum of .32mm but we prefer .4mm [ed note: 0.016"] thick. I have contacted every plater in the country (Guatemala) -- they do not "experiment" so we are on our own.

Our need is estimated to be 2000 clips and 1500 magnets per year. Also we are somewhat space limited -- a process that requires ten different baths even if it is less costly would not be as suitable as one that requires less space but is more costly. Any suggestions or advice would be greatly appreciated.
Sincerely ,

Robert Lackey
Field Effect Transistor Co. - Teculutan , Zacapa , Guatemala
  ^- Privately contact this inquirer -^


January 2019

A. Hi Robert. 3500 parts per year is only 15-20 per working day, so your production needs are not far beyond an experimental laboratory. But the only practical way to get the copper on them is probably electroplating, and these thicknesses are in the range of usual electroforming thicknesses and will likely require a plating time of almost a full day.

Before plating, the parts will require electrocleaning, rinsing, acid dip neutralization, rinsing, Wood's Nickel Striking, and rinsing before the copper plating. A possible alternative for less space is sandblasting followed by rinsing and Woods's Nickel Striking.

The plating is thick enough that maybe, depending on the shape of the parts, you can rely on a shrink-wrap cohesion effect more than adhesion to keep the copper attached to the parts. So maybe you can just sandblast the parts, rinse off the dust, and quickly start copper plating without the strike. (Must the nickel plating be retained?)

Years ago I was involved with the re-plating of the ironwork of Philadelphia city hall's William Penn clock tower; the original plating (acid copper plating directly onto iron & steel) was in the same general thickness range as you are contemplating and worked for many decades ... but once it became perforated there was rapid horrible undercutting corrosion because there was zero adhesion.

Regards,

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Ted Mooney, P.E. RET
finishing.com - Pine Beach, New Jersey
Aloha -- an idea worth spreading


January 12, 2019

Q. Thank you mister Mooney for your advice ... it sounds like it is doable. You asked if the nickel is necessary -- no, I just mentioned it because it was there, but I believe good adhesion is necessary because of flexing and the high amps that will be passing through the part.

I do have a few follow up questions if you don't mind --
1. in this application sand blasting is unacceptable due to the stress risers it would leave (it is a spring) but we have bead blasting, hot caustic soda bath, hot ferric chloride bath (with or without 5% nitric acid ) would any of these do what the sand blasting was intended to do?
2. after the Wood's Nickel Strike you say to copper plate , but a quick search of the internet turns up at least a dozen different copper plating methods, does it matter which one I choose? (many chemicals are not available here , for example we make our own Ferric chloride , so having several choices is a good thing from a chemical availability aspect).
Thank you in Advance.
Sincerely,

Robert Lackey [returning]
Field Effect Transistor Co. - Teculutan Zacapa Guatemala


January 2019

A. Hi again Robert. If at all possible you should be buying your plating solutions from a reputable plating process provider. If that is impossible, then you need to at least build a good plating library so you can research the matter.

Old nickel plating is difficult to activate for good adhesion even with a Wood's Nickel Strike. And chemically removing it without proprietaries or creating an environmental mess with nitric acid is difficult; blasting is better. Personally I would guess the best procedure for good adhesion on springs with old nickel plating would be to blast the old nickel off, then either nickel strike or cyanide copper strike, then acid copper plate.

But you don't build a plating plant based on theory. You need to try these things before you build a plant to do them.

Regards,

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Ted Mooney, P.E. RET
finishing.com - Pine Beach, New Jersey
Aloha -- an idea worth spreading



January 5, 2020

Q. Hi - for a 6th grade science experiment we are copper plating US 5 cent (Nickel) coins in a 500 CuSO4 solution with 9v battery and increasing amounts of Sulphuric acid - the problem is our weighing scale has a d=0.1 g and we are not seeing any more than 0.1 grams or at best 0.2 g for the highest acid levels - but we can clearly see that the Copper is pushed onto the coin and the alligator clip - are we saturating the coin ? Does copper deposit stop after the first level of coating? How can we show the gradients of acidity vs Copper deposited if we are "over plating"?

Anand Venugopal
Student - San Jose, California


January 2020

affil. link
Electronic scale

A. Hi Anand. Sorry to have to say this but, unfortunately, your experiment is not a good one. The variable that you are varying (acid concentration) does not approach the heart of the matter of what electroplating is really about as a science, and your constants (like 9V battery) are poorly chosen (9V is WAY too much; 3 V is plenty, and probably too much), and a scale which is incapable of measuring what is going on really isn't much use. Apologies :-(

Please see our paper "Faraday's Law of Electrolysis for Plating" which explains what the science of electroplating is really about. Then I think you will rethink your experiment and figure out a better way to structure it. Good luck.

Regards,

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Ted Mooney, P.E. RET
finishing.com - Pine Beach, New Jersey
Aloha -- an idea worth spreading

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