Acids and bases - what are they?

Every liquid you see will probably be either an acid or a base. The only exception would be distilled water. Distilled water is just water. That's it. Most water you drink has ions (electrically charged particles) in it.

Those ions in the solution make something acidic or basic. In your body, there are small compounds called amino acids. Those are acids. In fruits, there is something called citric acid. That's an acid, too. But what about baking soda? When you put that in water, it makes a base. Vinegar is also an acid.

Scientists use something called the pH scale to measure how acidic or basic a liquid is. The scale goes from values very close to 0 through 14. Distilled water is 7 (right in the middle). Acids are found between a number very close to 0 and 7. Bases are from 7 to 14. Most of the liquids you find everyday have a pH near 7. They are either a little below or a little above that mark. When you start looking at the pH of chemicals, the numbers go to the extremes.

If you ever go into a chemistry lab, you could find solutions with a pH of 1, and others with a pH of 14. There are also very strong acids with pH values below 1, such as battery acid. Bases with pH values near 14 include drain cleaner and sodium hydroxide (NaOH). Such chemicals are very dangerous.

When learning about acids and bases, there are some definitions you should know:

* Acid: A solution that has an excess of H+ ions. It comes from the Latin word acidus that means "sharp".

* Base: A solution that has an excess of OH- ions. Another word for base is alkali.

* Aqueous: A solution that is mainly water. Think about the word aquarium. Aqua means water.

* Strong Acid: An acid that has a very low pH (0-4).

* Strong Base: A base that has a very high pH (10-14).

* Weak Acid: An acid that only partially ionises in an aqueous solution. That means not every molecule breaks apart. They usually have a pH close to 7 (3-6).

* Weak Base: A base that only partially ionises in an aqueous solution. That means not every molecule breaks apart. They usually have a pH close to 7 (8-10).

* Neutral: A solution that has a pH of 7. It is neither acidic nor basic.

What really happens in those solutions? It gets a little tricky here. We'll give you the straight answer. Acids are compounds that break into hydrogen (H+) ions and another compound, when placed in an aqueous solution. Bases are compounds that break up into hydroxide (OH) ions and another compound, when placed in an aqueous solution.

Let's change the wording a bit. If you have an ionic compound and you put it in water, it will break apart into two ions. If one of those ions is H+, the solution is acidic. If one of the ions is OH-, the solution is basic. There are other ions that make acidic and basic solutions, but we won't be talking about them here.

That pH scale we talked about is actually a measure of the number of H+ ions in a solution. If there are a lot of H+ ions, the pH is very low. If there are a lot of OH- ions, that means the number of H+ ions is very low, so the pH is high.