Why do pennies turn brown

Patina is a coating of different compounds that serve as a protection to copper rather than corrode the metal. In simple terms, aside from oxidizing copper attracts minerals from the dirt and everything around it. This happens when people handle the coins. In the long run, copper alloy pennies turn brown eventually through this process. Because of the properties of this metal, copper pennies change to a brownish color over time.

You must be logged in to post a comment. These coins are dated with the year and are considered collector's items, though they are not exceptionally rare. A silver coin with a later date may have been caused by one of two methods.

First, a popular science experiment for chemistry students is to use a penny to explain how electroplating works. As part of this experiment, students dip copper pennies into zinc, which covers the copper and gives the penny a shiny silver color. It is also possible that a regular copper penny was dipped in acid, which removes the thin copper coating, leaving only the silver-hued zinc core. Emily Beach works in the commercial construction industry in Maryland.

Green Building Council in and is in the process of working towards an Architectural Hardware Consultant certification from the Door and Hardware Institute. She received a bachelor's degree in economics and management from Goucher College in Towson, Maryland. Corrosion Like all materials made from copper, pennies are subject to corrosion. How to Rust a Penny. Was one or five minutes more effective in cleaning the pennies overall? Can you think of why time would be important? Were there any cleaning methods where the time didn't matter, so the "1 Minute" and "5 Minutes" pennies are equally clean?

Why do you think this might be? Compare all of the cleaned pennies with the control ones. Which penny looks the cleanest compared with the control? Which is still the most tarnished? If you took a picture at the beginning, go back and compare each penny's cleanliness before and after being cleaned. Which penny is the cleanest compared with its before picture? Which is the least clean?

Extra: Test even longer periods of time with each of the cleaning methods. What is the optimal time to leave the pennies in the cleaning solution? Extra: Test whether these cleaning solutions work on other types of coins. What do your results tell you about the special properties of copper pennies?

Extra: Can you think of other safe household acids you could test? What about soda? Orange juice? Build a Cooler. Get smart. Sign up for our email newsletter.

Sign Up. Support science journalism. Knowledge awaits. See Subscription Options Already a subscriber? Rather than having whole copper atoms in the liquid, you've got copper ions, copper atoms that are missing two electrons.

These ions are positively charged. Now add two steel nails and a screw to the mixture. Steel is a metal made by combining iron, other metals, and carbon.

As you found out when you cleaned your pennies, your mixture of salt and vinegar is really good at dissolving metals and metal oxides.

When you put the steel nail in the mixture, some of the iron dissolves. Like the copper atoms, each of the iron atoms that dissolves leaves two electrons behind. So you've got positively charged iron ions floating in your vinegar with the positively charged copper ions. Originally, the steel nail was neutrally charged-but when the iron ions left their electrons behind, the nail then became neg-atively charged.

And remember what we said way back at the beginning of this section: negative charges attract positive charges. The negative charges on the nail attract positive charges in the liquid. Both the iron ions and the copper ions are positively charged. The copper ions are more strongly attracted to the negative charge than the iron ions, so they stick to the negatively charged nail, forming a coating of copper on the steel.

Each water molecule is made up of two hydrogen atoms and an oxygen atom. In an acid like vinegar or lemon juice , lots of hydrogen ions hydrogen atoms that are missing an electron are floating around. In the chemical reactions at the surface of the screw, some of these hydrogen ions join and form hydrogen gas.

The bubbles that you see coming off the screw are made of hydrogen gas.