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 solution is hydrophobic.

Step 1: Understand the Terminology

To solve this problem, we need to understand the terms presented in the answer choices such as emulsion, colloid, hydrophobic, and hydrophilic. An emulsion is a type of colloidal system where both components are liquids. A "colloid" is a broad category of mixtures where one substance is dispersed evenly throughout another, and it can include emulsions, gels, and sols. Something that is hydrophobic repels water, while something that is hydrophilic attracts water.

Step 2: Identify the Solution Type for Fe(OH)3

Fe(OH)3 is a colloid composed of small particles dispersed in water. In this type of colloidal solution, the dispersed phase (Fe(OH)3) does not interact well with water, making it hydrophobic. Hydrophobic colloids have dispersed particles that do not mix well with the surrounding water.

Step 3: Evaluate the Answer Choices

Using the definitions and information about Fe(OH)3, evaluate which option accurately describes it. The solution is a colloid due to the dispersed particles, but more specifically, it is a hydrophobic mixture because the Fe(OH)3 particles do not have an affinity for water.

Step 4: Select the Correct Answer

Since Fe(OH)3 in water forms a colloidal solution where the particles are hydrophobic, the correct answer from the choices given is (c) hydrophobic.

Key Concepts

Hydrophobic Colloids

Hydrophobic colloids are unique types of colloidal solutions where the dispersed particles show little to no affinity for the surrounding solvent, usually water. Essentially, these particles prefer to stay together rather than mix with the solvent. This characteristic is what makes them hydrophobic.

• Hydrophobic colloids are common in nature and play significant roles in various biological and physical processes.
• They often require stabilizing agents, known as emulsifiers or surfactants, to enhance their stability and prevent the particles from clumping together.
• Examples include colloidal systems like certain paint solutions and biological membranes.

In the absence of stabilizers, particles in a hydrophobic colloid can quickly aggregate due to their innate dislike for the solvent. This can lead to the separation of phases, where the dispersed phase pulls away from the solvent. Knowing this helps understand the behaviors and uses of hydrophobic colloids in various applications.

Colloidal Solutions

Colloidal solutions, also known simply as colloids, are mixtures where very small particles of one substance are evenly dispersed throughout another. The dispersed particles are microscopically small, ranging between 1 nm and 1000 nm in diameter, which allows them to stay suspended in the solvent without settling out.

• Colloids are unique because they exhibit properties of both homogeneous and heterogeneous mixtures.
• These solutions can scatter light, a phenomenon known as the Tyndall effect. This helps in identifying colloidal dispersions.
• Common examples include milk, smoke, jellies, and foams.

Colloidal solutions are classified based on the state of the dispersed phase and the dispersion medium. They are integral in fields like chemistry and materials science, due to their stability and unique optical properties. Understanding colloidal solutions is crucial for applications ranging from polymer chemistry to drug delivery systems.

Fe(OH)3 Colloid

Fe(OH)3, or iron(III) hydroxide, forms a notable example of a hydrophobic colloid when dispersed in water. In this colloidal system, the \(\text{Fe(OH)}_3\) particles are suspended in the water, creating an even mixture that exhibits typical colloidal properties.

• Iron(III) hydroxide particles do not interact favorably with water molecules, hence their categorization as hydrophobic.
• Such colloids might require stabilizers to maintain particle distribution and prevent aggregation.
• Fe(OH)3 colloidal solutions are often utilized in water purification processes as they can adsorb impurities effectively.

Understanding the nature of \(\text{Fe(OH)}_3\) and its interactions in colloidal form allows for insights into its applications in environmental science and engineering. As a result, Fe(OH)3 colloids are pivotal in areas like wastewater treatment and other chemical processes where suspension stability is integral to the operation.