Problem 102 - A Complete Resource Book in Chemistry for JEE Main

Question

Sodium salts of which of these acids can be used in making Soaps? (a) Stearic Acid (b) Palmitic Acid (c) Tartaric Acid (d) Lauric Acid

Step-by-Step Solution

Answer

Sodium salts of stearic, palmitic, and lauric acids can be used in making soaps.

Step 1: Identify the Purpose of Sodium Salts

Soaps are typically made from sodium salts of fatty acids. A fatty acid is an acid that contains a long alkyl chain. The sodium salt of these fatty acids reacts with water to form soap through a process called saponification.

Step 2: Examine Each Acid

Review each option to determine if the acid is a fatty acid: - Stearic Acid: A common fatty acid. - Palmitic Acid: A common fatty acid. - Tartaric Acid: Not a fatty acid (it's an organic dicarboxylic acid). - Lauric Acid: A common fatty acid.

Step 3: Determine Eligible Acids for Soap Making

Sodium salts of fatty acids are used for making soaps. Therefore, look for the acids that are fatty acids in the options: - Stearic Acid (Sodium Stearate) - Palmitic Acid (Sodium Palmitate) - Lauric Acid (Sodium Laurate)

Step 4: Conclude Based on Eligibility

The acids that can be used for making soaps are stearic acid, palmitic acid, and lauric acid. Tartaric acid cannot be used as it is not a fatty acid.

Key Concepts

Saponification

Saponification is a fundamental chemical reaction that transforms fats or oils into soap and alcohol through the action of an alkali, commonly sodium hydroxide (NaOH). This process is the backbone of soap making. When you combine sodium salts with fatty acids, they react with the alkali, leading to the formation of soap and glycerol.

• The fatty acid chain in a lipid interacts with sodium ions during saponification.
• Saponification is an irreversible reaction, meaning once it occurs, it cannot revert back to its original form.
• This process is exothermic, which means it releases heat.

Understanding saponification is crucial in predicting how different oils and sodium salts will behave when making soap. The mixture, once saponified, results in a solid product ready for personal or commercial use.

Soap Making

Soap making is both an art and a science, involving the combination of oils or fats with an alkali substance. This process results in soap, which cleans due to its molecular structure.

• Soap molecules have two parts: a hydrophilic head, which attracts water, and a hydrophobic tail, which repels water but attracts grease and grime.
• The hydrophobic tails latch onto the dirt, while the hydrophilic heads bond with the water, effectively removing dirt when rinsed away.

Commercial and homemade soaps often vary in their composition, but the principle of mixing sodium salts with oils through saponification remains the same. It is essential to use the right type of fatty acids, like those from stearic, palmitic, or lauric acid, to ensure the soap's efficiency and consistency.

Sodium Salts

Sodium salts are integral for soap production because they form the soap's base when combined with fatty acids. For example, when stearic acid reacts with sodium hydroxide, sodium stearate—a common soap—is produced.

• The sodium salts of fatty acids are responsible for the texture and cleansing efficacy of soap.
• Palmitic and lauric acids, when neutralized with sodium, form sodium palmitate and sodium laurate, respectively.
• These sodium salts dissolve in water, creating a lather that suspends and helps remove dirt, oil, and other impurities from surfaces.

It's important to note that not all sodium salts can form soap. Only those derived from specific fatty acids, like stearic, palmitic, and lauric acids, are ideal for producing effective soap products.