GATE (TF) Textile 2009 Question Paper Solution | GATE/2009/TF/43

Question 43 (Textile Engineering & Fibre Science)

Saponification with sodium hydroxide is done to increase the soil release property of

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Option A is correct.

Frequently Asked Questions | FAQs

What is the role of sodium hydroxide in saponification?

Sodium hydroxide (NaOH), also known as caustic soda or lye, plays a crucial role in the process of saponification. Saponification is the chemical reaction between a fatty acid and an alkali, such as sodium hydroxide, resulting in the formation of soap.
Here’s how sodium hydroxide contributes to the saponification process:

Hydrolysis of Fats: Sodium hydroxide acts as a strong base and facilitates the hydrolysis of fats or triglycerides. Triglycerides are esters composed of fatty acids and glycerol. When sodium hydroxide reacts with the triglycerides, it breaks the ester bonds, resulting in the separation of the fatty acids from the glycerol molecule.

Formation of Soap: The hydrolysis of fats produces fatty acid salts, which are the main components of soap. Sodium hydroxide reacts with the fatty acids released from the triglycerides, forming sodium salts of the fatty acids, also known as soap molecules. These soap molecules are amphiphilic, meaning they have both hydrophilic (water-loving) and hydrophobic (water-repelling) properties.

Emulsification and Cleaning: The soap molecules produced during saponification have a unique structure that allows them to act as surfactants. The hydrophobic “tail” of the soap molecule attaches to dirt, oil, and other non-polar substances, while the hydrophilic “head” interacts with water. This emulsifying action helps in the removal of dirt and oil from surfaces and makes them more easily rinsed away.

Alkaline Environment: Sodium hydroxide creates an alkaline environment during saponification. The alkalinity of the reaction mixture aids in the efficient hydrolysis of fats and the formation of soap. The high pH helps solubilize the fatty acids and allows for the transformation of the fatty acids into soap molecules.

It’s important to note that the saponification process is carefully controlled to ensure the proper balance of reactants and to prevent excess sodium hydroxide from being left in the final soap product. After saponification, the soap is typically washed or neutralized to remove any residual sodium hydroxide and adjust the pH to a suitable level.

Sodium hydroxide is a commonly used alkali in the saponification of solid soaps, whereas potassium hydroxide (KOH) is often used in the saponification of liquid soaps. Both alkalis serve a similar role in the saponification process, but they result in slightly different properties of the final soap products.

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