Problem 50 - A Complete Resource Book in Chemistry for JEE Main

Question

A colloidal solution of \(\mathrm{Fe}(\mathrm{OH})_{3}\) in water is called (a) emulsion (b) colloid (c) hydrophobic (d) hydrophilic

Step-by-Step Solution

Answer

The colloidal solution of \(Fe(OH)_3\) in water is called hydrophobic.

Step 1: Understanding Colloidal Solutions

A colloidal solution is a mixture where one substance is dispersed evenly throughout another. In this context, we're considering whether the colloidal solution of \(Fe(OH)_3\) in water has hydrophobic or hydrophilic properties.

Step 2: Hydrophobic vs Hydrophilic

A hydrophobic colloidal solution doesn't have an affinity for water and tends to repel it. Conversely, a hydrophilic colloidal solution has a strong attraction to water and can easily mix or stay dispersed. Knowing this distinction allows us to analyze the substance \(Fe(OH)_3\) in water.

Step 3: Analyzing the Properties of \(Fe(OH)_3\ in Water

Given that \(Fe(OH)_3\), when made into a colloidal solution in water, doesn't easily dissolve and can be unstable, we traditionally categorize it as hydrophobic. However, methods exist to stabilize it and make it behave hydrophilic.

Step 4: Solution Analysis

The statement indicates that the colloidal solution of \(Fe(OH)_3\) in water is called something specific. Considering that \(Fe(OH)_3\) is typically hydrophobic but stabilized using other agents, the solution is referred to as hydrophobic.

Key Concepts

Hydrophobic vs Hydrophilic

In the world of chemistry, understanding whether a substance is hydrophobic or hydrophilic can help predict its behavior in water. **Hydrophobic** literally means "water-fearing." Substances with this property tend not to interact well with water and often repel it. Examples include many oils and fats. These substances tend to form separate layers when mixed with water.

On the other hand, **hydrophilic** means "water-loving." These substances have a chemical attraction to water and can mix or dissolve easily in it. Hydrophilic materials often contain polar groups that interact favorably with water molecules. This makes them dispersible in water, creating stable solutions.

In essence, the terms hydrophobic and hydrophilic describe a substance's affinity for water, crucial for understanding how substances behave in aqueous environments.

Properties of Fe(OH)3

Iron(III) hydroxide, or \(Fe(OH)_3\), is a substance with fascinating properties when it comes to its colloidal behavior. When formed into a colloidal solution, it doesn't dissolve easily. Instead, it disperses in water, forming a cloudy or turbid solution. This characteristic is often attributed to its hydrophobic nature, which means \(Fe(OH)_3\) tends to repel water and cluster together, causing instability.

Despite being traditionally considered hydrophobic, \(Fe(OH)_3\) can be stabilized through different methods, altering its behavior in water.

One significant property of \(Fe(OH)_3\) is its ability to become hydrolyzed in water, leading to the formation of a gel-like structure when concentration increases. This can complicate its use but also opens up avenues for applications where gel formation is needed, such as in certain types of water treatments.

Stabilizing Colloidal Solutions

Stabilizing colloidal solutions is crucial to ensure that the dispersed particles remain evenly spread and don't clump together. In cases like that of \(Fe(OH)_3\), this stabilization can be achieved using several methods.

**Adding Electrolytes:** Certain electrolytes can provide a charge to the particles, causing them to repel each other and remain distributed in the solution. This electrostatic stabilization is one common method.

**Using Surface Active Agents:** Compounds like surfactants or polymers, which contain both hydrophilic and hydrophobic parts, can coat colloidal particles. This coating imparts a stabilizing layer, preventing particles from coming together.

These techniques change the interaction between particles and water, transforming a hydrophobic colloid like \(Fe(OH)_3\) into a more stable system. As a result, we observe what originally was a hydrophobic substance behaving in a more hydrophilic manner, capable of forming stable colloidal solutions.