Acids and Bases

For thousands of years humans have known that vinegar and lemon juice taste sour. But it was not until a few hundred years ago that it was discovered why these things taste sour. It is because they are acids. The term acid actually means “sour” in Latin. So what exactly are acids and bases, and how do they affect things?

Acids tend to taste sour and are corrosive to metals. They become less acidic when they are mixed with a base. Bases feel slippery and become less basic when mixed with acids. Mixing acids and bases can cancel out or neutralize their extreme effects. In the late 1800s, the Swedish scientist Svante Arrhenius proposed that water can dissolve many compounds by separating them into ions. He said that acids are compounds that contain hydrogen and can dissolved in water to release hydrogen ions into solution. He defined bases as substances that dissolve in water to release hydroxide ions into solution. His definitions of acids and bases helped to explain many things, like why all acids and bases have similar properties to each other. This also explains that acids and bases counteract each other.

Although Arrhenius helped explain some aspects of acid/base chemistry, his theories are not completely true. For example, baking soda can act like a base even though it does not contain hydroxide ions. So, in 1923 the Danish scientist Johannes Bronstead proposed similar things to Arrhenius that refined his theory. He defined an acid as anything that can donate a hydrogen ion and a base as any substance that can accept a hydrogen ion.

Under the Bronstead –Lowry definition, both acids and bases are related of the concentration of hydrogen ions present. Acids increase the concentration of them, while bases decrease it by accepting them. Therefore, how acidic or basic something is can be measures by its hydrogen ion concentration. In 1909, the Danish biochemist Soren Sorensen invented the pH scale for measuring acidity.

We learned in class that pure water falls exactly on 7 on the pH scale, because it is completely neutral. As we go farther down the scale the substances start to get more and more acidic. For example, stomach acid is very acidic and is at about 1 on the pH scale. If you were to vomit on yourself and pass out, your skin would be burned by the acid. Ammonia is very basic and is at about 11 on the pH scale. Also, each whole value below 7 is ten times more acidic. This is also true in that for each whole pH value above 7 the substance becomes 10 times more basic.

You can tell if something is an acid or a base it you put litmus paper in it. When litmus paper touches an acid, the paper changes to red. When it touches a base, the paper changes to blue. By comparing the color of the paper to a chart, you could determine how strong or weak that acid or base is. If you have ever done an experiment like this, then you saw what was an acid was and what was a base, as well as how strong they are.


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