Salt And Vinegar On Copper
Needed:
- A copper cent
- Vinegar
- Salt
- A plate
Experiment:
Sprinkle a little salt on the coin, pour on some vinegar, and the coin will be cleaned beautifully. Let it stand for a while, and the copper coin begins to corrode and turn green.
Explanation:
Salt, or sodium chloride, combines with acetic acid from the vinegar to produce sodium acetate and hydrogen chloride. Hydrogen chloride is a strong acid and the combination of it and sodium acetate rapidly cleans the surface of the penny (most pennies are 95% copper, 3% zinc, and 2% tin on their surface). The cleaning process leaves a very pure metal surface which quickly corrodes when exposed to the water, oxygen, and carbon dioxide from the air. Can you now explain why the copper domes often seen on buildings appear greenish?
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