Question

The aggregations of fatty acid anions that form when a soap is added to water are called __________.

Short answer

The aggregations of fatty acid anions that form when a soap is added to water are called micelles.

Step-by-step solution

1. Structure of Soap and Fatty Acid Anions

A soap molecule is composed of a long hydrocarbon chain with a carboxylate group (-COO-) at the head. When a soap is added to water, the carboxylate group dissociates into a carboxylate anion and a hydrogen ion. The carboxylate anion has a negatively charged head, which is attracted to the polar water molecules, while the hydrocarbon tail is nonpolar and repelled by water.

2. Interaction of Soap with Water and Fatty Acids

When a soap is added to water, the polar head of the carboxylate anion interacts with the polar water molecules through hydrogen bonding, while the nonpolar tail interacts with nonpolar substances such as oil, grease, or fatty acids. As a result, soap molecules form structures that can emulsify or dissolve these nonpolar substances in water, allowing them to be washed away.

3. Formation of Soap Aggregations

As more soap molecules gather around the nonpolar substances, they form larger structures known as aggregates. In these aggregates, the polar heads of the soap molecules face outward, interacting with the polar water molecules, while the nonpolar tails face inward, surrounding or encapsulating the nonpolar substances.

4. Name of the Aggregations

These soap aggregates that form when soap is added to water and encapsulate nonpolar substances are called micelles.

Answer

The aggregations of fatty acid anions that form when a soap is added to water are called micelles.

Key concepts

Structure of Soap

Understanding the structure of soap is key to comprehending how it cleans. A soap molecule features two distinct parts: a long hydrocarbon chain, which is hydrophobic (or water-repelling), and a carboxylate group at one end, making the head of the molecule hydrophilic (water-attracting). This dual nature is what gives soap its cleaning superpowers. With its long, nonpolar tail, soap can latch onto oils and dirt, which are also nonpolar. This 'tail' loves to avoid water and is more at home with other nonpolar substances like grease. On the flip side, the polar 'head' of the soap molecule prefers to hobnob with water molecules, thanks to the negative charge it carries. This polar attraction is crucial in making the next steps of the cleaning process possible.

Interaction of Soap with Water

When soap encounters water, its molecular structure leads to an interesting dance. The hydrophilic head is immediately attracted to water molecules, while the hydrophobic tail shies away, seeking refuge with other hydrophobic entities. This contradictory relationship propels the chemical bond of the soap molecule to break down, releasing a carboxylate anion and a hydrogen ion. As more soap is added to the mix, the molecules arrange themselves in a specific pattern where the hydrophobic tails cluster together and the hydrophilic heads point outwards. This arrangement allows for water and soap to co-exist, enabling soap to trap particles of dirt and oil and completely transform the cleaning process.

Formation of Soap Aggregations

The transformation reaches its peak when soap aggregations, known as micelles, form in water. Picture a spherical structure where countless soap molecules create an outer shell with their hydrophilic heads facing the watery environment, protecting the hydrophobic tails huddled inside. Inside this micelle, nonpolar substances like oil are sequestered, effectively encapsulated by the nonpolar tails, forming a convenient transport mechanism to remove them from surfaces. These micelles, which are washable and stable in the aqueous solution, are the soap's answer to the question of how to mix oil with water, and they are how soap achieves its ultimate goal: a thorough cleanse.