Zinc vs. Electricity
Make pictures on copper using zinc and electricity!
- Put on protective gloves and eyewear.
- Conduct the experiment on the plastic tray.
- Do not allow chemicals to come into contact with the eyes or mouth.
- Keep young children, animals and those not wearing eye protection away from the experimental area.
- Store this experimental set out of reach of children under 12 years of age.
- Clean all equipment after use.
- Make sure that all containers are fully closed and properly stored after use.
- Ensure that all empty containers are disposed of properly.
- Do not use any equipment which has not been supplied with the set or recommended in the instructions for use.
- Do not replace foodstuffs in original container. Dispose of immediately.
- In case of eye contact: Wash out eye with plenty of water, holding eye open if necessary. Seek immediate medical advice.
- If swallowed: Wash out mouth with water, drink some fresh water. Do not induce vomiting. Seek immediate medical advice.
- In case of inhalation: Remove person to fresh air.
- In case of skin contact and burns: Wash affected area with plenty of water for at least 10 minutes.
- In case of doubt, seek medical advice without delay. Take the chemical and its container with you.
- In case of injury always seek medical advice.
- The incorrect use of chemicals can cause injury and damage to health. Only carry out those experiments which are listed in the instructions.
- This experimental set is for use only by children over 12 years.
- Because children’s abilities vary so much, even within age groups, supervising adults should exercise discretion as to which experiments are suitable and safe for them. The instructions should enable supervisors to assess any experiment to establish its suitability for a particular child.
- The supervising adult should discuss the warnings and safety information with the child or children before commencing the experiments. Particular attention should be paid to the safe handling of acids, alkalis and flammable liquids.
- The area surrounding the experiment should be kept clear of any obstructions and away from the storage of food. It should be well lit and ventilated and close to a water supply. A solid table with a heat resistant top should be provided
- Substances in non-reclosable packaging should be used up (completely) during the course of one experiment, i.e. after opening the package.
FAQ and troubleshooting
Something most likely went wrong with the electrical circuit. First, double check that the batteries are inserted correctly into the battery case according to their polarity. Next, make sure that the wires with crocodile clips are connected exactly as shown in the instructions and that the zinc rod isn’t touching the copper coin. If this doesn’t help, check that the batteries are charged by either by plugging them into another appliance or by testing them with a special instrument called a multimeter.
It’s possible that the copper disk wasn’t cleaned thoroughly enough with the abrasive sponge. Try the experiment again, but make sure to thoroughly clean off the leftover zinc layer. Keep your protective gloves on—otherwise you’ll leave oily fingerprints, and the zinc won’t efficiently deposit onto the copper.
Unfortunately, the experiment likely won’t succeed this time. Bubbling is a side reaction that you can prevent by keeping the coin farther away from the zinc rod.
If your drawing didn’t turn out quite right on the first try, or if you’d like to draw something different on your coin, thoroughly clean both sides of your coin with the abrasive sponge. This will remove the old zinc layer and clear away any possible dust or oily contaminants. Then, repeat the experiment from the very beginning.
Yes, this experiment will work if you reuse the original solution. Just make sure to thoroughly clean the coin with the abrasive sponge in order to remove the old zinc layer and any contaminants.
Any impurities on the surface of the copper disk may prevent electroplating. Thoroughly clean the disk using a sponge to remove any problematic materials.
Draw some patterns on the coin using a black crayon.
Prepare a solution of zinc salt, which will be the second metal used in this process.
Connect the positively charged electrode (the red one) to the zinc wire, and the negatively charged electrode (the black one) to the copper disk.
Initiate the electroplating process (depositing zinc onto the copper disk) by immersing the disk and the wire in the zinc sulfate solution.
Disassemble the setup and clean the crayon drawings off the disk.
Dispose of solid waste together with household garbage. Pour solutions down the sink. Wash with an excess of water.
Is it necessary to clean the surface of the copper disk?
Dust particles and impurities must be completely removed from the disk. Otherwise, they will block any electrical charge transfer from the battery to the copper atoms and won’t allow the copper atoms to “attract” zinc atoms. The resulting pattern will come out uneven, and in the last step, the zinc will end up on the napkin instead of the disk.
Copper is resistant to oxidation from air exposure, and doesn’t develop an oxide film. However, every time we touch the copper disk, it accumulates dust and oil. Even fingerprints invisible to the human eye can potentially interfere with the experiment, which is why it’s best to wear gloves during the procedure.
Why do we have to use a crayon to draw the patterns?
To create our patterns, we need a water-insoluble material that can serve as a point insulator to protect our copper surface from the impending electrochemical reaction. A crayon is paraffin-based, which perfectly suits our purposes. Paraffin is a blend of hydrocarbons obtained via petroleum rectification. It is used to make candles and—upon the addition of pigments—colorful crayons. Due to its molecular nature, paraffin doesn’t react with water. Moreover, paraffin doesn’t conduct electricity, i.e. it is a dielectric material.
A paraffin molecule consists solely of carbon C and hydrogen H atoms. These atoms are connected in such a way that the molecule as a whole is chemically inert, meaning that it rarely participates in chemical reactions and only in certain conditions. Finally, paraffin is hydrophobic, meaning that it repels water.
What happens in the beaker?
In the beaker, we can observe electrolysis, a chemical reaction driven by a direct electric current.
Besides electricity, such a reaction also requires a rather specific medium—an electrolyte solution. An electrolyte is a compound that can dissociate into ions and, therefore, can conduct electricity. In our experiment, zinc sulfate ZnSO4 serves as our electrolyte.
ZnSO4 → Zn2+ + SO42-
This solution conducts electricity due to the flow of ions within it.
Let’s examine this process in detail.
Starting from the batteries, electricity flows through the whole system: through the wires, the copper disk, the zinc wire, and the zinc sulfate ZnSO4 solution connecting them.
The batteries lend the zinc wire a positive charge. As a result, some zinc atoms are released from the wire into the solution in the form of ions Zn2+:
Zn0 – 2e– → Zn2+
These ions drift from the zinc wire towards the copper disk, which carries a negative charge. They then participate in an electrochemical reaction and turn back into zinc atoms, accumulating on the surface of the disk:
Zn2+ + 2e– → Zn0
As a result of these reactions, the copper turns silvery, while the spots covered with the crayon drawing remain unchanged. These spots are sheltered from the zinc by a thin layer of paraffin wax.
Why do we have to flip the copper disk?
Electricity drives the zinc ions in the solution towards the copper disk. However, this driving force depends heavily on distance: the far side of the disk “attracts” much fewer zinc ions than the side closest to the zinc wire. If we want to evenly cover the disk on both sides, we have to flip it about halfway through the reaction.
Why can we wipe off the crayon but not the zinc?
Adhesion, or, in this case, metals’ abilities to stick together, depends on the properties of said metals’ crystal lattices. Much hinges on how well they match and how strong of a bond they can form on a phase boundary. Copper and zinc suit each other very well, which is why the zinc coating is hard to wipe off of the disk. Nevertheless, if electrolysis is conducted too rapidly, then the obtained metal layer will turn out loose and easily removable. The substances used to make crayons do not resemble metal at all and, thus, do not interact with metals. That’s why we can easily wipe the crayon marks from the disk.
Why does zinc plate copper, and not the other way around?
Zinc is a stronger reducing agent than copper. If we immerse a zinc plate in a solution of copper salts, then copper will precipitate from the solution, and zinc will dissolve.
This electrochemical series of metals will help us understand what’s going on:
Li → K → Ba → Ca → Mg → Al → Zn → Fe → Sn → Pb → H → Cu → Hg → Ag → Pt → Au
This series exhibits metals in order from most active to least active. The most active metals are also the strongest reducing agents. Therefore, in theory, a copper disk will attract the ions of all the metals that are to the left of copper in the series.
Electroplating and coin counterfeiting
In general, electroplating involves depositing one metal onto another metal with the help of an electric current. Interestingly, this process was first discovered while experimenting with coins. Moritz von Jacobi, a physicist, was the first to come up with the idea to conduct such an experiment. Jacobi later destroyed the coin he made for honesty’s sake; nevertheless, it didn’t take long for counterfeiters to figure out they could make money off this discovery.
Coins produced via electroplating are exact copies of an original, including even its tiniest details. This counterfeiting method requires some intensive labor, yet it’s so effective that counterfeiters are still using it. Obviously, regular change isn’t worth counterfeiting, but collectibles are!
There is a way to tell the difference. An original coin has to be copied from both sides, thus, a fake coin is made of two separate metal details: the obverse (heads) and the reverse (tails). These two details have to be joined and somehow glued together. This process leaves a fake coin with a seam on the rim that must be thoroughly concealed: its traces are the main warning sign that you’ve got a counterfeit on your hands.
Moreover, a counterfeit coin is hollow inside, which is easily betrayed by its weight. Experienced counterfeiters fill a fake coin with cheap metal, which still can be detected by measuring its electrical conductivity.
However, electroplating isn’t just for counterfeiters. This technique is legally employed at mints to manufacture coins that are then put in requisition. It would be too expensive to make golden coins out of pure gold. Rather, they are made of steel and then coated with brass (lending them a reddish color) or aluminum bronze (lending them a more yellowish tint).