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Supported by Rolls-Royce

Polishing pennies

Make old pennies sparkle with some simple chemical reactions.
Plan a session with this activity

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You’ll need

  • Old pennies
  • White wine vinegar
  • Salt
  • Baking powder
  • Non-metallic spoons
  • Non-metallic bowls
  • Paper towels

To watch in full screen, double click the video

 

Before you begin

  • Set up three experiment stations with the necessary equipment:
    • one only using vinegar
    • one using vinegar and salt
    • one using vinegar and baking powder

Keep things safe

  1. Everyone should discuss how to keep themselves and others safe when conducting experiments like this one, which uses the power of chemical reactions for cleaning pennies. Highlight the importance of:
    • reading all warning labels on the materials being used
    • carefully following directions
    • wearing eye protection
    • wearing gloves
    • wearing protective clothing (such as a lab coat) or something with long sleeves
    • tying back long hair
    • keeping all chemicals away from your mouth, nose and eyes
    • not consuming any food or drink near an experiment.
  1. Everyone should make sure they are dressed suitably and safely.

Get ready to experiment

  1. Make some predictions about what might happen in the three experiments. What will happen when the penny touches the vinegar? How long will it take to see results? What will the chemical reactions between the salt, vinegar and baking powder look like? Which experiment will be most effective, and why?
  2. Everyone should split into three small teams. Each team should start at one of the experiment stations. Repeat the experiments three times so each team gets a go, or encourage everyone to record their findings and report back to the other teams.
  1. One member of the team should pour enough vinegar into a bowl to form a shallow puddle.
  2. Another member should fill a second bowl with water.
  3. Use a spoon to carefully place several pennies in the vinegar. Don’t overcrowd the bowl with pennies. Make sure each one is fully submerged.
  4. Leave the pennies to sit in the bowl for between 10 and 30 seconds. As the pennies soak, you should notice the dirt melting away from them. Gently shake the bowl to remove even more of the dirt.
  5. One member of the team should use a spoon to remove the pennies from the vinegar and put them into the bowl of water.
  6. Everyone should use their hands to get the last of the grime off the pennies.
  7. Once they are clean, everyone should take the pennies out of the water and place them on paper towels to dry.
  1. One member of the team should pour enough vinegar into a bowl to form a shallow puddle.
  2. Another member should fill a second bowl with water.
  3. Carefully stir a teaspoon of salt into the vinegar so it dissolves.
  4. Use a spoon to carefully place several pennies in the vinegar and salt solution. Don’t overcrowd the bowl with pennies. Make sure each one is fully submerged.
  5. Leave the pennies to sit in the bowl for between 10 and 30 seconds. As the pennies soak, you should notice the dirt melting away from them. Gently shake the bowl to remove even more of the dirt.
  6. One member of the team should use a spoon to remove the pennies from the vinegar and salt solution, and put them into the bowl of water.
  7. Everyone should use their hands to get the last of the grime off the pennies.
  8. Once they are clean, everyone should take the pennies out of the water and place them on paper towels to dry.
  1. One member of the team should pour enough vinegar into a bowl to form a shallow puddle.
  2. Another member should fill a second bowl with water.
  3. Carefully stir two teaspoons of baking powder into the vinegar.
  4. Use a spoon to carefully place several pennies in the vinegar and baking powder solution. Don’t overcrowd the bowl with pennies. Make sure each one is fully submerged.
  5. Leave the pennies to sit in the bowl for between 10 and 30 seconds. As the pennies soak, you should notice the dirt melting away from them. Gently shake the bowl to remove even more of the dirt.
  6. One member of the team should use a spoon to remove the pennies from the vinegar and baking powder solution, and put them into the bowl of water.
  7. Everyone should use their hands to get the last of the grime off the pennies.
  8. Once they are clean, everyone should take the pennies out of the water and place them on paper towels to dry.

 

Examine the results

  1. The teams should gather together with their pennies to discuss their results. What did you observe from your experiments? Are some pennies cleaner than others?
  2. Everyone should discuss what happened when salt or baking powder was added to the vinegar. Was a chemical reaction observed? What was it? (The baking powder caused the mixture to fizz as carbonic acid and sodium acetate were produced by the reaction.)
  3. Everyone should discuss how they think the vinegar cleaned the pennies. (Pennies are made from copper, which reacts over time with the oxygen in the air. This is called ‘oxidisation’, and makes the pennies look dull and dirty. Vinegar is also called acetic acid, and its acidity makes it able to strip off the copper oxide.)
  4. Everyone should discuss which vinegar mixture was the best at cleaning the pennies. Which came out the cleanest? (Adding salt or baking powder will strengthen the vinegar’s ability to remove the copper oxide.)
  5. Everyone should reflect on the predictions they made. Did any of them come true? Was anything surprising?

Reflection

This activity was about learning new skills. Why might the cleaning power of vinegar be useful to know about? (It’s a household item that can be useful for cleaning lots of things, and isn’t harmful like other products). We made sure this experiment was done as safely as possible. Why was that important? What other experiments would you like to do?

This activity was also about problem-solving. We all made predictions about what we thought might happen in the experiments. What led you to make those predictions? What did you learn from the ones that did and didn’t come true?

Safety

All activities must be safely managed. You must complete a thorough risk assessment and take appropriate steps to reduce risk. Use the safety checklist to help you plan and risk assess your activity. Always get approval for the activity, and have suitable supervision and an InTouch process.

Chemicals

This task involves the use of potentially harmful fluids or chemicals. Make sure you follow all relevant safety guidance. Make sure you dispose of them appropriately too, in line with safety guidance.

Science

Supervise young people, and only do science activities that are advised and age appropriate for your section. Test activities first, to make sure you’re confident you can lead them safely. Use protective clothing where necessary.

Ensure the vinegar solutions are disposed of carefully and that everyone washes their hands thoroughly after each experiment.

Work in larger teams to give more support to individuals. Set up more experiment stations with other acidic liquids, including lemon juice (citric acid) and cola (phosphoric acid), reacting them with salt to see which can best remove copper oxide.

Make it accessible

All Scout activities should be inclusive and accessible.

Cubs Scientist Activity Badge

Create more copper cleaning solutions by using different acidic liquids. While vinegar contains acetic acid, lemon juice contains citric acid and Coca-Cola contains phosphoric acid. Repeat this experiment using lemon juice and Coca-Cola to explore which liquid, when reacted with salt, is best at removing copper oxide.

The best liquid will be the one will the lowest pH number. The pH scale measures how much acid is in a solution, and the lower this number is, the more acidic it is. Depending on the vinegar, its pH is likely to measure between 2.4 and 4.5. Coca-Cola generally comes in lower, at about a 2.5 pH. Lemon juice is the most acidic of all, with a pH of about 2.