Zinc-carbon battery

Make a real zinc-carbon battery!

Difficulty:
Danger:
Duration:
15 minutes

Reagents

Safety

  • Put on protective gloves and eyewear.
  • Conduct the experiment on the plastic tray.
General safety rules
  • 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.
General first aid information
  • 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.
Advice for supervising adults
  • 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

I can’t insert the graphite electrode/funnel/cotton cylinder into the silicone tube.

All of these items should fit snugly in the tube. Don't be afraid to apply more force if need be. You can also try using another graphite electrode or cotton cylinder. And, of course, you can always ask an adult for help.

What should I draw on the clock dial?

You can draw anything you want – let your imagination run wild!

The clock isn’t working. What should I do?

Make sure the screw is touching the metal clamp in the clock mechanism, and the graphite electrode on the opposite end of the battery is touching the metal part of the clock mechanism housing.

Why isn’t the LED glowing?

If you have assembled the two batteries and connected them correctly to the LED, but the LED isn’t glowing — don’t worry! This is probably easy to fix.

First of all, try switching the wires. Electric current can only run through an LED in one direction. Make sure the crocodile clips are clamped to the metal, not the insulation.

Next, check all the connections. Are all the components of the circuit connected securely? The screw must be touching the springs in the connector, and the graphite rods on the opposite ends of the batteries must be touching the metal parts of the connector housing. Finally, make sure that all the wires are fixed securely to the LED and to the connector.

If none of these steps help, try using a different LED or assembling a new battery.

Is it OK to use regular batteries instead of the ones we make in this experiment?

We do not recommend connecting regular batteries to the LEDs from the kit. This could potentially result in the LEDs overheating and/or malfunctioning.

Step-by-step instructions

Mix some manganese dioxide MnO2 with graphite C. MnO2 is going to "pull" electrons from zinc Zn, while graphite will allow the electrons to travel through the mixture.

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Insert a graphite electrode into a silicone tube. This will be the battery body.

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Pour some of your MnO2 and C mixture into your battery cartridge.

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Put a cotton cylinder into the cartridge and soak it with ammonium chloride NH4Cl solution. Then insert a bolt plated with zinc Zn—and your battery is ready!

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To make use of your newly-made battery, assemble the clock.

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Zn is keen to give its electrons e- away. Electrons are negatively charged, and that's why the Zn side of the battery is connected to the "-" of the clock. MnO2 is willing to take the electrons that zinc gives away, and its side is marked "+". The electrons can't pass through the cotton or the NH4Cl solution, however, so they need another route. Unlike the NH4Cl solution, the clock's internal workings do allow electrons through. But their passage isn't free: in return, the electrons make the clock tick. That's how all electrical devices work.

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Assemble another battery and use both of them together to power an LED.

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Disposal

Please refer to local regulations when disposing of chemicals. Dispose of other solid waste with household garbage. Pour leftover solutions down the sink. Wash with an excess of water.

Scientific description

If the electrons go from zinc Zn to manganese dioxide MnO2, can't you just put the "+" wire of your device  in some MnO2 powder , connect the "−" wire to a piece of zinc , and call it a day? Well, not so fast.

As soon as a negatively-charged electron leaves zinc Zn , the latter becomes positively charged and wants to pull the electron back. That is, unless it can get rid of its charge. And that's where the solution of ammonium chloride NH4Cl  in water H2 comes in.

Metallic Zn  can release the positively-charged Zn2+  particles into the solution, and thus get rid of its charge. Something similar happens with MnO2 , which gains negatively-charged electrons e . To become uncharged, it ultimately gives its oxygens O  to water H2, forming OH . Zn2+  and OH  particles are charged, but they, unlike electrons, can move freely in the solution, so they spread out and mix in the NH4Cl soaked cotton, making it evenly uncharged too.

There are countless ways to make chemicals work to move electrons in wires and this one isn't the simplest. But your battery is chemically identical to commercially produced zinc-carbon batteries. The reason for that is the fortunate combination of readily available ingredients and the lack of free-flowing liquids in the construction of the battery and the absence of gaseous products of the reaction.

How do zinc-carbon batteries work?

Such a battery (also called as zinc-manganese or manganese battery) is a chemical source of electric current that relies on an oxidation-reduction (redox) reaction between manganese dioxide (MnO2) and zinc powder (Zn). Such a reaction involves the transfer of electrons from one element (the reducer) to another element (the oxidizer).

Our battery is divided into two sections, separated by wadding: one section holds the oxidizer MnO2, and the other contains the reductant Zn. When the battery isn’t connected to anything, these isolated substances cannot react with each other. But when the crocodile clips are connected to a diode, the circuit is closed and the reaction can begin: electrons start migrating from the zinc section to the manganese section. They move from the bolt through the springs and the black wire to the diode (which starts glowing!), then continue on through the red wire, and finally through the graphite rod to the manganese dioxide (MnO2) section.

Why do we need the graphite powder?

The battery will work only if the electric current can flow “unobstructed,” so the agents inside the battery must be able to conduct electricity very well.

Unlike graphite, manganese dioxide MnO2 is not a good conductor, but a mixture of MnO2 and graphite powder is a fine conductor for such a battery.

Why do we need the NH4Cl solution?

As electrons move from the zinc section to the manganese dioxide section, they create an electron excess in the latter. Meanwhile, an electron shortage arises in the zinc section as electrons move away from it. These must be balanced for the battery to work reliably for an extended period of time.

Ammonium chloride NH4Cl is primarily intended to be a source of hydrogen ions H+ that can balance out the electron excess in the manganese dioxide MnO2 section.

At the same time, chloride ions Cl- balance out the electron shortage in the zinc section.

Also, on the zinc side, the reaction creates Zn2+, which readily forms insoluble compounds in these conditions. If these compounds accumulate, the electric current will eventually just stop. Once again, ammonium chloride comes to the rescue: the ammonia NH3 obtained during the reaction forms a compound with Zn2+ that is easily soluble in water.

That’s interesting!