Acidity of Carboxyl Groups: Description & Analysis

Instructor: Amanda Robb

Amanda holds a Masters in Science from Tufts Medical School in Cellular and Molecular Physiology. She has taught high school Biology and Physics for 8 years.

This lesson will explain the acidic properties of carboxylic acids. First, we'll review the different definitions of an acid, and then we'll look at what structures within a carboxylic acid act as such. Lastly, we'll look at how strong carboxylic acids are.

What Are Acids?

Imagine drinking a cold glass of orange juice and eating a bagel for breakfast. After cleaning your dishes, you hop in the car and drive to school. What do all these typical activities have in common? They all depend on acids.

Acids, like the acid in your orange juice, your stomach and your car battery, all have specific properties that allow them to be somewhat to very corrosive. Acids can be defined in three main ways in science, but the definition we'll be focusing on here is the Bronsted-Lowry definition.

In the Bronsted-Lowry definition, acids are molecules that can donate hydrogen ions and bases are molecules that can accept hydrogen ions. Acids and bases are measured on the pH scale, which measures the concentration of hydrogen ions. A pH of 0-6 is acidic, 7 is neutral and 8-14 is basic.

Different acids have different pH values depending on their strength and concentration. The pH of orange juice is between 3 and 4, whereas the pH of the battery acid in your car is as low as 1.

Carboxylic Acid Uses

Carboxylic acids are organic molecules that contain a carboxyl group, or a carbon bound to a hydroxyl group and an oxygen molecule.

The structure of a carboxyl group
carboxyl group

Carboxylic acids are important biological molecules. They can be found in amino acids, which make up the proteins inside our cells. Proteins are needed for cell structure and function, and without them we wouldn't be able to stay alive!

Carboxylic acids are also found in metabolic products, such as lactic acid, citric acid and others. Carboxylic acids are also important in manufacturing. Carboxylic acids can be found in the synthesis of textiles, plastics and even aspirin.

Strength of Carboxylic Acids

As the name implies, carboxylic acids are a type of Bronsted-Lowry acid. The hydrogen ion on the hydroxyl group is able to be donated to other molecules in solution, making it an acid. If carboxylic acids are dissolved in water, they can donate the hydrogen ion to the water, creating hydronium ions.

The strength of the carboxylic acid depends on the organic molecule it is attached to. Overall, carboxylic acids tend to be stronger acids, but not as strong as mineral acids, such as the sulfuric acid found in car batteries or the hydrochloric acid found in our stomachs.

Let's look at what makes certain carboxylic acids stronger than others. When a carboxylic acid donates its hydrogen ion, it gains a negative charge. The better the molecule is able to stabilize the negative charge, the more likely it is to lose the hydrogen ion and act as an acid. So, what types of structures will stabilize the negative charge?

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