Hydrolysis: Definition, Reaction, Equation & Example

Instructor: A Ray Tatum

A. Ray has taught junior high, high school and college English and has a master's degree in curriculum.

Have you ever wondered why the hydrolysis reaction is used to break table sugar, or sucrose, into glucose and fructose sugars? Continue reading to learn about the hydrolysis reaction, including examples of different types of hydrolysis reactions.

What Is a Hydrolysis Reaction?

When we digest food, what helps break down the material we eat? Correct! The answer is water. At each meal, whether you're eating a breakfast muffin or an amazing filet mignon, a liquid of some sort is on standby to help you digest your food. In fact, your body's initial mechanism of digestion is a great example of hydrolysis. Hydrolysis is the process of using water to break down a molecule into two parts. The prefix 'hydro-' means water, while the suffix '-lysis' means to break down. Hence, if you see the word hydrolysis you can automatically think of the term, 'reaction with water.'

Hydrolysis is quite useful in both biology and chemistry. Biological applications range from breaking sugar molecules down in our body to participating in the release of stored energy from ATP. Let's look at ATP as an example. If we zoom into the cells of our body, we will run across a little guy, a protein, called ATP or Adenosine Tri-Phosphate.

Biology Application of Hydrolysis Using ATP
biology ATP

I know, I know, you may be wondering what does biology, let alone ATP, have to do with hydrolysis? Well, this little molecule is a powerhouse in our body that stores energy converted from the food we eat. In order to release this stored energy, the bonds from ATP molecules must be broken. How do you suppose those bonds are broken? That's right! Our friend hydrolysis comes to the rescue.

So, what about applications of hydrolysis in chemistry? Hydrolysis is widely used in industry to break down chemicals into smaller fractions or pieces. For example, a compound called organophosphate ester can be hydrolyzed, or undergo a hydrolysis reaction. This hydrolysis aids in the production of insect killers and pesticide sprays.

General Equation for Hydrolysis

A very simple illustration of the hydrolysis equation is shown below. As you can see, there is a long chain that needs to be broken into two separate parts. When water is added, a bond is broken between the atoms used to form that long chain. Given what we now know about this equation, let's explore the different types of hydrolysis reactions.

General Equation Applicable to Hydrolysis Reactions
general equation

Defining the Hydrolysis Reaction: Acid vs. Base

When you encounter a hydrolysis reaction, you will see three different types: salt, acid, and base hydrolysis. Although the mechanism of using water to break down a molecule applies to all types, the starting players, or reactants, vary. Pay careful attention to this as we go through each type.

A salt hydrolysis reaction involves the dissolving of a weak acid or base in water. A weak acid (or base) is simply a substance that only partially dissociates or breaks apart into ions in an aqueous solution, which is just another word for a water solution. An ion is a molecule or atom that carries a positive or negative charge. Illustration of the hydrolysis for table salt, or NaCl, is shown below.

Diagram of Salt Hydrolysis Reaction
salt

When we dump salt into a water solution, the molecule NaCl breaks apart into sodium ions (Na+) and chlorine ions (Cl-). What makes this a hydrolysis reaction is the function of water aiding to break apart NaCl into those ions.

As a side note, it is worth stating that hydrolysis reactions can also be conducted with organic compounds. However, there is one small problem with this reaction. Water and organic compounds typically do not react readily with each other. The key word here is, 'readily.' In other words, this type of reaction needs a little push or jumpstart in order to work.

This is because water is a very polar molecule. Polarity deals with the separation of charge in either a bond or entire molecule. Most organic compounds are not as polar as water. Less polar and very polar molecules do not like to mingle together. As you might suspect, performing a hydrolysis reaction with both molecules is quite hard to do. However, if we introduce a mediator called a catalyst, not only will these two molecules work together but the reaction will proceed to completion. A catalyst is a molecule that speeds up the rate of the reaction without being consumed.

This leads us to the other two reaction types, acid and base hydrolysis reactions. Acids and/or bases can behave as catalysts, functioning to drive a hydrolysis reaction towards completion. An acid hydrolysis reaction involves water behaving as an acid by donating a proton (H+) in solution.

Example of Acid Hydrolysis For Acetic Acid
acid

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