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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