Let them shine!

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Have you ever wondered why coins look dull brown after some time? It is an example of chemical reaction in everyday life.

First we need to know that the basic building block for all matter in the universe is atoms, which are extremely small. The copper used for coins is made up mainly of copper atoms. Two atoms form a molecule. A chemical reaction takes place when two or more atoms or molecules interact and form a different molecule or compound (combination of molecules). For example, a molecule called copper oxide forms when copper atoms join oxygen atoms in the air. This process is called oxidation. It is the copper oxide that makes coins look dirty with a dull, slightly darkened appearance.

To make dull coins shiny again, we create another chemical reaction that will remove the oxide from the coins. We mix acid acetic (vinegar, lemon juice, etc.) and sodium chloride (salt) to form a new substance called hydrochloric acid. Sit the coins in the acid for a few minutes and rinse off the solution with water. Now admire the shininess!

You have probably see coins turning blue-green. This is also oxidation in action. If the coins are not rinsed off after soaking in hydrochloric acid in the above experiment, the acid acetic on the coins helps the copper in the coins easily react with the oxygen in the air. A blue-green coloured compound called malachite is formed.

Watch the following video to observe all these chemical reactions.


Inquiry – Digging Deeper

We know that acids cause chemical reaction with copper and dissolve copper oxide. Almost all liquids are either acids or bases to some degree. Watch the following video to find out the differences between acids and bases. Would bases also do the job? Find out from the experiment on the Activity Sheet!