Sometimes, coins have a strange, rough, and dark look to them.They undergo through a process called oxidation. Oxidation is the chemical reaction when a substance comes across with oxygen molecules and forms salt and releases hydrogen gas. Oxidation is also one half of the Redox Reactions which is the transfer of electrons between chemical species. And the other half of the Redox Reactions is Reduction which is the gain of electrons.
When metals react with oxygen, it causes tarnish and rust.
Why does this happen?
- When the copper atoms in a penny join with oxygen atoms in the air, it creates copper oxide which forms on the penny. This is what makes the coin look old, dirty, and rusty. It also creates tarnish and makes the coin look like it has discoloration.
- The quarter, nickel, and dime endure through this process too. However, these three coins contain the element nickel in them as well. The nickel protects the coins from the effects of the moisture.
- This is why pennies tend to rust more rapidly than the other coins especially because it has a copper plating which exposes it more to oxygen. The nickel is an nonreactive element and does not combine with oxygen at room temperature as fast as the pennies.
Coins that have oxidized look similar to this:
Question to keep in mind:
- Which of the seven products used in this experiment will be the most effective in cleaning US coins?
- Why didn't some of the products did or did not work as well as the others?
Stand in order to hold the coins in place.
The components I used were:
1. Baking Soda
2. Rubbing Alcohol
3. Orange Juice
4. Lemon Juice
6. Dish Soap
I hypothesized that both the vinegar and rubbing alcohol would clean the coins the best. Since they are very strong household liquids, I made the educated guess that it would make a greater reaction than any of the other components.
In order to figure out if my hypothesis was correct, I first only hung half of the coins into the cups filled with the liquids. I also wrapped the cup with the rubbing alcohol with a piece of a rubber glove since it evaporates when exposed to air. And I left the coins there for a few hours.
In the end, orange juice, lemon juice, and Coca-Cola were the best liquids to clean the coins. They did the best job than the other components because they are strong acids.
What are Acids and Bases?
The seven different are separated into two different classes of substances. These two are called Acids and Bases. Acids are chemicals that donate hydrogen ions(H3O+) and have are usually sour. And bases give off hydroxide ions (OH−) and have a bitter taste. In order to tell the difference, either acid or base is dissolved in water. Water is used because it contains both an equal amount of hydrogen and hydroxide ions which then makes it an acid and a base. If there are more hydrogen ions the solution is acidic, but if it has more hydroxide ions, the solution is basic.
The pH Scale:
The pH Scale is what distinguishes acids from bases and determines how much hydrogen ions are in a substance. The higher the hydrogen ions, the lower the pH value is. The scale is measured from 1-14. The most acidic liquids rate from 1-6, the most basic goes from 8-14, and 7 would be neutral.
pH Values of the components:
Baking Soda: 9
Lemon Juice: 2
Rubbing Alcohol: 5.5
Orange Juice: 3
Dish Soap: 7.5
Since the orange juice, lemon juice, and coca-cola have the lowest pH value and dissolved the oxide in the coins, this means that acids when in contact with the oxidation of the coins, cleans the coin the best. And since the baking soda and dish soap have the highest pH value and they did not clean the coins, it makes sense to say that a base does not react well with metal oxide. The more Hydrogen ion concentration, the stronger the acid. And the more hydroxide ion, the stronger the base. Active metals like copper and nickel can displace hydrogen ions from acids. The more hydrogen atoms in the acid the stronger the acid and the lower its pH and the more clean the coin will be.