What are acids and bases

Acid-base chemistry

We already got to know acids and bases in middle school. As a small repetition, here is the definition according to Brønstedt:

  • Acids are substances that release protons (H +) and are therefore also called proton donors.
  • Bases are substances that take up protons (H +) and are therefore also called proton acceptors.
  • An acid-base reaction is a chemical reaction in which a proton transfer takes place from the acid to the base.
  • Protolysis is a chemical reaction in which a proton changes from an acid to a base.

Important: An acid can only give off protons if someone picks them up (a base) and vice versa.

In an acid-base reaction, every acid becomes a corresponding base and every base becomes a corresponding acid.

Example: Sulfuric acid and ammonia

The base HSO− 4, which corresponds to sulfuric acid, still has a proton which it can give off, so it can continue to react as an acid.

Since sulfuric acid can react twice as an acid and therefore gives off a total of two protons, we call it a biprotonic acid. The corresponding base HSO− 4 formed in the first reaction is a special substance because it can react as a base and as an acid.

If a substance can react both as an acid and as a base, i.e. can release and absorb protons, this substance is called an ampholyte. Whether this substance reacts as an acid or a base depends on the reactant. A classic example of an ampholyte is water.

Such an ampholyte can also react with itself. This process is called \ textbf {autoprotolysis}. Let's look at the ampholyte water: