Difference Between Acetic Acid and Citric Acid

Main Difference – Acetic Acid vs Citric Acid

Acetic acid and citric acid are two compounds which are often used as food additives. Therefore, these compounds are found in the kitchen; acetic acid can be found in vinegar and citric acid can be found in lime juice. The main difference between acetic acid and citric acid is that acetic acid is a monobasic acid whereas citric acid is a tribasic acid.

Key Areas Covered

1. What is Acetic Acid
      – Definition, Properties, Applications
2. What is Citric Acid
      – Definition, Properties, Applications
3. Similarities Between Acetic Acid and Citric Acid
      – Outline of Common Features
4. Difference Between Acetic Acid and Citric Acid
      – Comparison of Key Differences

Key Terms: Acetic Acid, C₂H₄O₂, CH₃COOH, C₃H₅O(COOH)₃, C₆H₈O₇, Citric Acid, Ethanoic Acid, Molecular Formula, Monobasic Acid, Tribasic Acid, Weak Acid

What is Acetic Acid

Acetic acid is also known as Ethanoic acid. It is composed of C, H and O atoms. The molecular formula of acetic acid is C₂H₄O₂. But the most common way of representing acetic acid is CH₃COOH. This formula indicates some details about acetic acid structure. Acetic acid is a carboxylic acid. It has only one carboxylic acid group. It is composed of a methyl group (-CH₃) that is attached to the carbon atom of the carboxylic acid group. The molar mass of acetic acid is about 60 g/mol.

Figure 01: Chemical Structure of Acetic Acid

At room temperature and pressure, acetic acid is a colorless liquid and has a very pungent odor. The boiling point of this liquid is about 118^oC. pK_a value for this acid is about 4.76. Therefore, acetic acid is a weak acid, and it partially dissociates in water. But acetic acid is miscible in water.

In aqueous solutions, acetic acid dissociates, releasing the Hydrogen atom of the carboxylic group as an H⁺ ion. This is the reason for the acidity of the acetic acid. Due to the presence of –O-H bond in the carboxylic group, acetic acid can have strong hydrogen bonds in its solid phase.

Acetic acid can mix with either polar solvents or non-polar solvents. The polar group of acetic acid is a carboxylic group. It causes mixing of acetic acid with polar solvents. The methyl group is a non-polar group and cause the mixing of acetic acid with non-polar solvents.

Applications of Acetic Acid

• Production of vinegar
• Preparation of metal acetates
• Solvents for resins
• Production of acetic anhydride

What is Citric Acid

Citric acid is a weak acid most commonly found in citrus fruits. It is a tricarboxylic acid with the chemical formula C₆H₈O₇. The common way of representing the chemical formula of citric acid is C₃H₅O(COOH)₃. This indicates that citric acid has three carboxylic acid groups (-COOH). Apart from that, a hydroxyl group(-OH) is also present.

The molar mass of citric acid is about 192 g/mol. It is an odorless compound. Citric acid is easily crystallized from its solution. These crystals appear as a white powder. The boiling point of citric acid is about 310^oC. Citric acid is miscible in water and in anhydrous ethanol. Due to the presence of carboxylic groups, citric acid is capable of forming strong hydrogen bonds.

Figure 02: Chemical Structure of Citric Acid

Citric acid is a tribasic acid. It can release three protons (H⁺) per molecule. Therefore, it has three pKa values. pK_a1 is 3.13, pK_a2 is 4.76 and pK_a3 is 6.40. The biological role of citric acid is the citric acid cycle; a main metabolic pathway of animals and plants.

Applications of Citric Acid

• Used as a food additive
• Used as drink
• Act as a chelating agent
• Ingredient of some cosmetics

Figure 03: Citric acid is used in the Preparation of Food and Beverages

Similarities Between Acetic Acid and Citric Acid

• Acetic acid and citric acid are weak acids.
• They are often used as food additives.

Difference Between Acetic Acid and Citric Acid

Definition

Acetic Acid: Acetic acid is a useful weak acid that is found mainly in vinegar.

Citric Acid: Citric acid is a weak acid found in citrus fruits.

Acidity

Acetic Acid: Acetic acid is monobasic (has one replaceable hydrogen atom).

Citric Acid: Citric acid is tribasic (has three replaceable hydrogen atom).

Molar Mass

Acetic Acid: The molar mass of acetic acid is about 60 g/mol.

Citric Acid: The molar mass of citric acid is about 192 g/mol.

Chemical Formula

Acetic Acid: The Chemical formula of acetic acid is CH₃COOH.

Citric Acid: The Chemical formula of citric acid is C₃H₅O(COOH)₃.

Number of Carboxylic Acid Groups

Acetic Acid: Acetic acid has only one carboxylic acid group.

Citric Acid: Citric acid has three carboxylic acid groups.

Boiling Point

Acetic Acid: The boiling point of Acetic acid is about 118^oC.

Citric Acid: The boiling point of Citric acid is about 310^oC.

pK_a

Acetic Acid: Acetic acid has only one pK_a value.

Citric Acid: Citric acid has three pK_a values.

Conclusion

Both acetic acid and citric acid are very useful acid compounds. These compounds significantly contribute to small scale applications as well as to large-scale industries. The main difference between acetic acid and citric acid is that acetic acid is a monobasic acid whereas citric acid is a tribasic acid.

References:

1.”Acetic acid (CH3COOH).” Encyclopædia Britannica. Encyclopædia Britannica, inc., n.d. Web. Available here. 03 July 2017. 
2.”What is acetic acid .” Study.com. Study.com, n.d. Web. Available here. 03 July 2017.

Image Courtesy:

1. “Acetic-acid-2D-flat” By NEUROtiker – Own work (Public Domain) via Commons Wikimedia
2. “Zitronensäure – Citric acid” By Benjah-bmm27 – Own work (Public Domain) via Commons Wikimedia
3. “Oranges and orange juice” By USDA photo by Scott Bauer. Image Number K7237-8. (Public Domain) via Commons Wikimedia