Problem 12 - Arihant Objective Approach to Organic Chemistry for IIT JEE and NEET all Medical Entrances Part 4

Question

Which of the following represents soap? (a) \(\mathrm{C}_{17} \mathrm{H}_{35} \mathrm{COOK}\) (b) \(\mathrm{C}_{17} \mathrm{H}_{35} \mathrm{COOH}\) (d) \(\left(\mathrm{C}_{17} \mathrm{H}_{35} \mathrm{COO}\right)_{2} \mathrm{Ca}\) (c) \(\mathrm{C}_{15} \mathrm{H}_{31} \mathrm{COOH}\) (d) \(\left(\mathrm{C}_{17}+1_{35}^{\circ}-2\right)=[\) Manipal 2005]

Step-by-Step Solution

Answer

(a) \( \mathrm{C}_{17} \mathrm{H}_{35} \mathrm{COOK} \) represents soap.

Step 1: Understanding the Components

Identify the general chemical formula for soap and understand the function groups present in each option. Soap is generally formed by the saponification reaction, which produces a salt of a fatty acid.

Step 2: Identify the Chemical Formula of Soap

Consider the options: soaps are salts of fatty acids, generally sodium or potassium salts. Therefore, the formula of soap usually takes the form RCOONa or RCOOK (where R is a hydrocarbon chain).

Step 3: Evaluate Option (a)

The compound \( \mathrm{C}_{17} \mathrm{H}_{35} \mathrm{COOK} \)is a potassium salt of stearic acid. It fits the description of a soap, with the potassium ion forming a salt.

Step 4: Evaluate Option (b)

The compound \( \mathrm{C}_{17} \mathrm{H}_{35} \mathrm{COOH} \)is stearic acid, not a salt. This is not a soap because it has a carboxylic acid group without any metal ion (e.g., K or Na) forming a salt.

Step 5: Evaluate Option (c)

The compound\( \mathrm{C}_{15} \mathrm{H}_{31} \mathrm{COOH} \)is palmitic acid. This is also a fatty acid and not a salt, so it does not represent a soap.

Step 6: Evaluate Option (d)

The compound \( \left(\mathrm{C}_{17} \mathrm{H}_{35} \mathrm{COO}\right)_{2} \mathrm{Ca} \)is a calcium salt of stearic acid. While it is a salt of a fatty acid, it is referred to more commonly as a grease instead of a true soap (which is typically Na or K salt).

Step 7: Choose the Correct Answer

Based on evaluating each option, the correct representation of a soap is \( \mathrm{C}_{17} \mathrm{H}_{35} \mathrm{COOK} \), which is option (a).

Key Concepts

Saponification

In chemistry, saponification is a fascinating process responsible for turning fats and oils into soap. This transformation occurs when triglycerides, the molecules in fats and oils, react with a strong base such as sodium hydroxide (NaOH) or potassium hydroxide (KOH). The reaction is aptly named after the Latin word "sapo," meaning soap, due to its soap-producing nature.
During saponification, the triglyceride molecules are hydrolyzed—this means water molecules break the ester bonds. The result is glycerol and fatty acid salts, which we recognize as soap. These fatty acid salts are typically where the hydrocarbon chain joins a sodium or potassium ion, creating the well-known soap structure.

• The reaction is essential for soap production.
• Potassium hydroxide and sodium hydroxide are common reactants.

Saponification is an exothermic reaction, meaning it releases heat. This reaction is central to many industries and is widely used in creating not just soap but also various cleaning and skincare products.

Fatty Acids

Fatty acids are key players in soap production. They're carboxylic acids that generally have long aliphatic hydrocarbon chains. The number of carbon atoms in these chains can vary, usually ranging from 4 to 28. Fatty acids exist in various forms—saturated, where there are no double bonds between carbons, and unsaturated, featuring one or more double bonds.
In the world of soaps, fatty acids are essential because they represent the core components that react with alkalis (like KOH or NaOH) to form soap.

• Essential for the chemical structure of soap.
• Present in natural sources like animal fats and plant oils.

The two fatty acids often mentioned in soap making are stearic acid (\(\mathrm{C}_{17} \mathrm{H}_{35} \mathrm{COOH}\)) and palmitic acid (\(\mathrm{C}_{15} \mathrm{H}_{31} \mathrm{COOH}\)). While both are important, neither is used directly as soap without first undergoing saponification.

Potassium Salts

Potassium salts are integral to the identity of soaps used in various applications. These salts are generated when fatty acids react with potassium ions during saponification. The resulting potassium salts differ from sodium salts in one important aspect: they are softer.
This softness translates into a soap that dissolves more easily in water, making potassium salts ideal for products like liquid soaps.

• More soluble than their sodium counterparts.
• Primarily used in liquid soap products.

In the context of chemical formulas, potassium soaps are represented by compounds like \(\mathrm{C}_{17} \mathrm{H}_{35} \mathrm{COOK}\), which is a potassium salt of stearic acid. Such formulations are valued in the cosmetic and pharmaceutical industries for their ease of application and mildness on the skin.

Organic Chemistry

Organic chemistry is the backbone of understanding saponification, fatty acids, and the formation of soaps. It's a branch that focuses on the study of carbon-containing compounds, which include hydrocarbons and many other complex molecules. The principles of organic chemistry help elucidate how various organic molecules interact and transform.
Soap-making unites various concepts from organic chemistry, such as the chemistry of esters and carboxylic acids, which are integral parts of fatty acids.

• Provides the theoretical framework for understanding saponification.
• Explains molecular structures and reactions in soap creation.

Through organic chemistry, we grasp how triglycerides break down during saponification and how fatty acid salts, vital to soap, are formed. It's essential for anyone delving into how everyday products like soaps are chemically crafted.