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Electroplating for a school science project, page 3

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How come after electroplating the nickel with copper, the copper in the nickel fades and turns into blue green color. I used vinegar with salt 9 volts battery charger.

I put them in separate containers with vinegar using copper as the anode and the nickel as the cathode.

Marc Andres
- Laredo, Texas USA

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+ I'm not sure I understand you, Marc, but if you don't thoroughly rinse the vinegar off, and dry it, you will still have acid on it that is capable of dissolving copper back into blue-green copper ions. Ted Mooney, P.E. finishing.com Brick, New Jersey + Dear Mr. Mooney, After browsing through your website I stumbled upon an experiment you and another person had found to be quite effective in the electroplating of copper pennies. You used vinegar, sugar, and salt as the electrolytic solution/bath. I've tried and tested your mixture. I changed it a little however....: I used a six volt battery, the sanded down penny as the anode, and the "bright" penny as the cathode. I filled my transparent tank with 1 gallon of warm water. Then I added 1/8 cup of vinegar, salt and sugar. Once placed in the tank, the cathode immediately began to fizz. After ten minutes, and the re-application of the toothbrush cleaning, my "zinc" penny was quite remarkable. I'm not sure of what was being let out at the cathode, though. Can you please tell me what was being released and how this electroplating process took place even without a SALT of zinc serving as the electrolytic solution? How can this work if the electrolytic bath is not composed of ions of the plating metal? Any help you can give me would be much appreciated. (The purpose of my doing this is to show how simple household substances can electroplate dull objects). Thank you, Danielle Danielle W. [last name deleted for privacy by Editor]

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Hello Danielle, we're happy to hear that the experiment went well for you.

At the anode (the sanded penny) there is a positive charge, i.e., the battery is pulling electrons away. At the cathode (the penny being plated) there is a negative charge, i.e., the battery is supplying electrons.

So, what happens at each end of the cell then is reactions that are consistent with this electron activity.

At the anode, metallic zinc (Zn⁰) is available from the sanded penny. Remove two electrons per atom, pulled away by the battery, and you get Zn⁺⁺ ions of zinc dissolving into the solution. Also available at the anode is water , H⁺₂O^{- -}. Pull electrons away from the oxygen and you get oxygen gas.

At the cathode, electrons are added to the Zn⁺⁺ ions in solution, reducing it to metallic zinc Zn⁰. Also happening though, is electrons are being added to the water, causing the hydrogen in the H⁺₂O^{- -} to be reduced to H⁰, hydrogen gas.

There is a bit more to it, related to the fact that molecules of gases like hydrogen and oxygen usually contain two atoms rather than one, and that, depending on the pH, water may split into hydrogen gas and hydroxide (OH^- )ons rather than hydrogen gas and oxygen gas. But that's the general idea.

By the way, I note that some people mix-and-match pieces of experiments, and that's a good learning experience. Because of that I like to discourage people from using table salt (NaCl) in the experiments, suggesting the use of Epson salts MgSO₄ instead, because we don't want any possibility of chlorine gas Cl^- being released if people get carried away with increasing the voltage, concentration, and acidity.

Ted Mooney, P.E. finishing.com Brick, New Jersey

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+ Mr. Mooney & others, The "silver plating" mentioned in the first inquiry may well have been the mercury replacement reaction that I, too, did as a kid. Mercuric Nitrate solution, kept in a Skippy peanut butter jar, was quite useful for impressing sixth-grade girls with my "magic". Today, however, mercury is limited from common use by the knowledge that it is very toxic (to humans and in the environment). Mercury-containing hazardous wastes are some of the most worrisome by-products concerning industry today. Alas, no more slippery, shiny silver pennies! (I'm glad I learned chemistry when I did and lived to talk about it.) My hat is off to you, Mr. Mooney, for your concern about encouraging learning while advising caution and stimulating independent research. Thank you. John E. Softy - Mt. Airy, Maryland, USA

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Why does the copper leave the pennies and deposit on the iron? I need a simplified reason to explain to my 2nd grader. We're doing Immersion copper plating.

Aileen Paluck
- Sioux Falls, South Dakota

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Start by looking at the acid, Aileen. It consists of 2 kinds of ions paired together, cations and anions. For example, hydrochloric acid is H⁺Cl^-, where you have H⁺ (hydrogen) cations and Cl^- (chlorine) anions paired together in balance, forming HCl.

The Cl^- has a greater affinity for metal than for the hydrogen they were originally bound with. So the acid will dissolve Fe (iron) or Cu (copper), while releasing hydrogen gas, per these reactions:

2H⁺Cl^- + Fe⁰ --> H₂⁰ ^ (hydrogen gas) + Fe⁺⁺Cl₂^- and

2H⁺Cl^- + Cu⁰ --> H₂⁰ ^ (hydrogen gas) + Cu⁺⁺Cl₂^-

But copper is more noble than iron (wants to come out of solution and reform copper metal), so the reaction continues:

Cu⁺⁺Cl₂^- + Fe⁰ --> Fe⁺⁺Cl₂^- + Cu⁰

So what happens is the acid dissolves both copper and the iron, but the iron pairs better, so the Cl pairs with the iron, and the copper has no matching anion to keep it in solution, forcing it to fall out of solution and deposit on the iron article.

As soon as the iron object is lightly covered with copper, the reaction will stop.

Not a great explanation, but it's hard to explain this kind of chemistry to a second grader.

Ted Mooney, P.E. finishing.com Brick, New Jersey

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I am doing a science fair project and I want to electroplate quarters with copper using copper sulphate. what would I need to mix the copper sulphate with to make the solution? and what kind of volt battery would be best to use?

Mayra
- USA

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+++++ Hi, I would like to post a question to Tom Pullizzi, regarding his post. I was reading through to get some ideas for my school science experiment and I am quite interested in what you said. He suggested to change someone's project to rinsing? Does rinsing have anything to do with electroplating? And, are there any other types of experiments to show the concepts of electroplating apart from the plating/coating of metals? Jenna Mave - Singapore

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An old book of mine tell a VERY simple method of electroplating targeted towards kids if this is what you are talking about. It says to get 2 long wires (doesn't specify) and attached copper end to penny and nickel and the other to the positive terminal (penny) and negative terminal (nickel) of a 6 volt battery. it says to wrap wires around pencil and balance over glass jar with water (water used as the electrolyte). it is supposed to go through the water with the electrical current and copperplate the nickel and be scraped off easily. That the simplest method of electroplating I've come across so far.

Michele
- Venice, Florida

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But does it work, Michele? I doubt it because for the copper to get to the nickel, it has to travel there. And it does not travel as a solid in little flakes; rather it must dissolve in the solution as travel as a copper ion. But how are you going to dissolve copper in water?

If you think it works, please try it and tell us what you find.

Ted Mooney, P.E. finishing.com Brick, New Jersey

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WELL I'M LATE IN REGARD TO THE ABOVE QUESTION, but I ALSO TRIED THAT EXPERIMENT AND NO, IT DIDN'T WORK. I TRIED 4 TIMES AND NOTHING BUT DIRTY (BLUE-GRAY) WATER. MAYBE I DIDN'T ALLOW IT ENOUGH TIME (OVERNIGHT YIELDED NOTHING). ANYWAY I'm SORRY TO SAY OUR FASCINATION WITH PLATING HAS NOT ENDED because I AM WORKING ON A SCIENCE PROJECT WHICH IS WHY I'm ON YOUR SITE.

Raquel
- Miami, Florida, US

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No surprise here. Use vinegar instead of water, Raquel, and it will work. Maybe not great, but it will work.

Ted Mooney, P.E. finishing.com Brick, New Jersey

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A great and somewhat easy "experiment," (should be more of a demo for for any classroom presentation) is plating copper (Cu) with zinc (Zn).

Create a zinc salt solution by dissolving Zinc Chloride in distilled water. This breaks the Zinc Chloride into negatively charged zinc ions and positively charged polyatomic chloride ions. Using a 1 1/2 volt D-Cell battery, make a zinc strip your cathode and a copper strip your anode. The copper will soon become plated with with a silvery/grey coat of zinc.

** DO NOT USE MORE THAN 1 1/2 VOLT BATTERY. POTENTIALLY LETHAL CHLORINE GAS COULD BE GENERATED!**

When disposing of the Zinc Chloride solution follow the instrustions listed on the appropriate MSDS.

Jonathan Fields
- Mt. Vernon, Georgia

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April 12, 2011

I want to do an experiment for my 6th grade science fair that measures the effect of increasing voltage on the plating process. I intend to try to plate a dime with copper using a vinegar solution at several different voltages and evaluate the results. Since vinegar is a weak acid, you recommend using a copper cathode and running for several hours before plating to put some copper in solution. My question is: can I pre-prep several batches of the solution with copper cathodes and continue the plating with the dimes a day or two later, or is there some chemical process which will reduce the effectiveness of the solution if I wait?

Conor M
student - Poulsbo, Washington, USA

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