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acid, base, pH scale, litmus test
Imagine a game of basketball is being played between two middle school teams. One team is called the Eastside Acids. The other team is the Southside Bases. The two middle schools have played each other many times during the year. The Acids have won two games, and the Bases have also won two games. The Acids always wear red jerseys and red shoes. The Bases always wear blue jerseys and blue shoes. Both teams are very good, but they are very different. The Acids always play heavy metal music before the game begins. Listening to heavy metal helps them get ready to play. The players on the team say that it helps them be more explosive on the court.
This basketball game will help explain a very important part of chemistry. For thousands and thousands of years people have known that some foods have a sour taste. What foods taste sour to you? Have you ever tried to drink lemon juice before? Lemon juice is very, very sour. Vinegar is also very sour. In the past few hundred years scientists have figured out why some foods are sour. They are sour because they are acids! Robert Boyle was the first person to say that sour foods are acids.
Boyle separated acid from another group called base substances. Eggs are a type of base, so is baking soda. Bases feel slippery when you rub them between your fingers. All bases taste bitter. Can you think of some bitter tasting food? Broccoli has a bitter taste because broccoli is a base!
A lemon is sour and acidic.
Think about the basketball game again. Each team has seven players. They have a center, point guard, shooting guard, power forward, small forward, and two players on the bench. The players on the Acids are each numbered from 0 to 6 on their red jerseys. The players on the Bases are each numbered from 8 to 14 on their blue jerseys. The referee of the game even has his own number. His number is 7. The job of the referee is to stay in the middle. He does not play on either team. The referee does not care who wins or loses.
A Romanesco Broccoli. It has a different shape than the broccoli you might eat, but it is still a base .
The players in the basketball game are like the acids and bases we see everyday. Some acids and bases are very strong and others are weak. The strength of acids and bases are measured along a pH scale. Anything from 0 up to 7 on the pH scale is an acid. Anything above 7 up to 14 on the pH scale is a base. If something is pH 7 then it is neutral. It is not an acid or a base. Pure water is an example of something that is pH 7. Water is neutral, it is not an acid or a base. The acid in your stomach has a pH close to 1. Stomach acid is very acidic. Coffee is also acidic, but not as acidic as stomach acid. Coffee has a pH around 5. The stuff you have in your house to clean sinks and bathrooms is very basic. They have pHs of 12 or more. The ocean is less basic, it has a pH around 8.
Have you ever touched eggs? They feel slippery because they are a base.
To decide if something is an acid, base, or neutral we do a litmus test. For a litmus test you need litmus paper and any kind of substance. Lets say you have some lemon juice, baking soda, and pure water. If you place the lemon juice on the litmus paper the paper will turn red. It turns red because lemon juice is an acid, and acids always turn litmus paper red. If you place the baking soda on the litmus paper the paper will turn blue. All bases turn litmus paper blue. What do you think will happen when you put pure water on litmus paper? Nothing! The litmus paper will not change color because pure water is neutral. Pure water is not a base or an acid.
HCl or Hydrochloric acid found in your stomach and is so acidic that the litmus paper turns red just by holding it at the top of the bottle!