Question

Soaps are sodium salts of fatty acids. Which of the following fatty acids does not form soap-

• A. Butyric acid
• B. Oleic acid
• C. Palmitic acid
• D. Stearic acid

Answer 1

The correct option is A

Butyric acid

The explanation for the correct answer:

• Soaps are the metallic salts of fatty acids, and the most often used salts are sodium $\left(\mathrm{Na}\right)$ and potassium$\left(\mathrm{K}\right)$
• The general formula for soaps is ${\mathrm{RCOONa}}^{+}\mathrm{or}{\mathrm{RCOOK}}^{+}$ where $\mathrm{R}$ is the alkyl group of the parent fatty acid.
• Soaps are made with palmitic acid, stearic acid, oleic acid, and lauric acid.
• The hydrophilic (water-loving) part of the soap is the metallic ion, whereas the lipophilic (oil/fat-loving) part is the organic chain.

The explanation for the incorrect answer

Option (B)

Oleic acid or Cis-Oleic acid has formula of ${\mathrm{C}}_{18}{\mathrm{H}}_{34}{\mathrm{O}}_2$. Most abundant acid in adipose tissue and used to prepare soap.

Option (C)

Palmitic acid or Hexadecanoic acid has a formula ${\mathrm{C}}_{16}{\mathrm{H}}_{32}{\mathrm{O}}_2$obtained from Palm Oil. Used in the preparation of soap and also in cosmetics.

Option (D)

Stearic acid or Octadecanoic acid has formula ${\mathrm{C}}_{18}{\mathrm{H}}_{36}{\mathrm{O}}_2$ which is obtained from animal and plant fats and is used to prepare soap.

Hence, the correct answer is option (A).