Hydrolysis in Acid-Base Reactions

Instructor: Laura Foist

Laura has a Masters of Science in Food Science and Human Nutrition and has taught college Science.

Hydyolysis is the use of water to break apart molecules, in this lesson, you'll learn how water reacts in acidic and basic reactions to create important molecules.

Hydrolysis and Our Body

In our body, energy is stored as ATP. In order for us to use the energy in ATP, hydrolysis needs to break one of the phosphate groups off of the ATP making ADP. Hydrolysis is the process by which water is used to break a bond in a molecule.

Since water can act as either a base or as an acid, it is able to participate in a variety of reactions. In normal situations, some water will always ionize so that we have some positive ions and some negative ions. This is because the oxygen can either give up a hydrogen (forming a hydroxide anion) or take on another hydrogen (forming a hydronium ion).

Hydrolysis in Acid Reactions

It can get a little confusing to think about which reactions are acid reactions and which are basic reactions because for acidic hydrolysis the water is acting as a base, while for basic hydrolysis the water is acting as an acid. The way to keep this straight is to remember that hydrolysis refers to a molecule being broken with water. So what molecule is being broken? In acidic hydrolysis, it is an acidic molecule that is being broken. For the acidic molecule to be broken, the water (in the hydrolysis portion of the name) needs to act as a base. It works in the opposite way for basic hydrolysis.

Let's look at some acidic hydrolysis examples. For acidic hydrolysis to work, we react water with a weak acid such as acetic acid or hydrofluoric acid.

Acetic acid hydrolysis

The acetic acid reacts with the water, and the water acts as a base and accepts the hydrogen, breaking the oxygen hydrogen bond.

Hydrofluroic hydrolysis

In this example, the hydrofluoric acid reacts with the water, and the water acts as a base and accepts the hydrogen from the hydrofluoric acid. This breaks the fluoride-hydrogen bond, and we end up with a fluoride ion and a hydronium ion.

These reactions can now act as a catalyst for other reactions since we have a positive charge on the water and a negative charge on the acetic acid. Both of these compounds can now easily react with other compounds. For example, the water (hydronium ion) can react with an ester and break it into a carboxylic acid and an alcohol.

This hydronium ion is also what reacts with ATP to break the phosphate bond to release energy into the body.

Hydrolysis in Base Reactions

Hydrolysis in base reactions is very similar to hydrolysis in acid reactions, except now the water acts as a proton donor and becomes a hydroxide anion (OH).

Pyridine hydrolysis

Pyridine is a weak base so it can by hydrolyzed by water. In this reaction, the pyridine takes the hydrogen from the water breaking that oxygen-hydrogen bond.

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