Cleaning Coppers

Public summary: 

Those grubby coppers in your pocket or purse can be shined up in minutes, give it a try and find out how it works.

Removing copper oxides from coins.
Useful information
Kit List: 

Plastic containers (e.g. disposable cups) - broad shallow containers are generally better.
Cola drink (optional)
Copper/copper coated coins
Waste bin
Paper towels

Packing Away: 

NB: There is no box for this experiment.
Weak copper solutions can be poured down a drain, with excess running water.
Clean and dry non-disposable items (if there are any).
Wipe down surfaces.
Return unused solvents (vinegar etc.) to stores (box/pile).
Return money.

Frequency of use: 

In a nutshell
Copper coins are cleaned by putting them in vinegar to dissolve the copper oxide/copper chloride corrosion products, which are a lot more soluble in acid than the plain copper.

How to set up the experiment
Make up cup(s) of vinegar, ask children/parents for copper coins - the dirtier the better (which will be returned, clean!).

What you need to know during the experiment
(1) Corrosion is a result of the reaction of the metal with oxygen in air, forming the black solid copper oxide. You can compare it with rusting of iron and, for older kids, you can talk about the reaction being faster in the presence of moisture.
(2) The black copper oxide reacts with the acetic acid in vinegar to form copper acetate, which is soluble in water and forms a pale green solution.

Want to know more?
You can also make green copper acetate by putting lots of really dirty copper coins in vinegar.
The green colour of many copper salts can be seen on the surface of copper roofs and constructions like the Statue of Liberty. Although it is soluble in acid, under normal conditions it is very stable, preventing corrosion of the rest of the copper underneath the surface.
Reaction with cola is remarkable from the point of view of making the copper clean - it's very acidic - but you can't see it happening very well. You can ask what would happen if you put a tooth in it, and relate that to drinking lots of fizzy drinks.

Risk Assessment
Date risk assesment last checked: 
Wed, 09/01/2019
Risk assesment checked by: 
Grace Exley
Date risk assesment double checked: 
Sun, 13/01/2019
Risk assesment double-checked by: 
Polly Hooton
Risk Assessment: 

Clean coppers using vinegar, orange juice, coke, water etc.
Possibly dissolving enough copper to make the vinegar go green.

Hazard Risk Likelihood Severity Overall Mitigation Likelihood Severity Overall
Copper dissolved in liquid Ingestion of copper salts can lead to the creation of free radicals in the body (which can damage DNA). 3 4 12 Concentrations are very low, the tolerable ingestion limit of copper is about 10mg, much less than would be present in a container used to clean a couple of coppers.
Change acid every 10 coins and dispose of used solution down a drain immediately. Empty and rinse container.
If cleaning large numbers of coppers to observe green colour of solution use a closed (plastic) jar and tape down lid. Keep control of jar (at busy events may be advisable to tape jar to a length of string to prevent it "walking off").
Call a first aider in the event of ingestion.
2 2 4
Acids Use of lemon juice, coke, other culinary acids - will sting if they get into people's eyes or cuts. 4 2 8 Ensure children lower coins gently into solution. Encourage them to check for scratches before putting hands near solutions and to wipe fingers afterward.
Rinse out cuts, call first aider if required. If trained and confident to do so use sterile eye wash to clean out splash to eye.
2 1 2
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