Problem 35 - A Complete Resource Book in Chemistry for JEE Main

Question

The diameter of colloidal particle ranges from (a) \(10^{-9} \mathrm{~m}\) to \(10^{-6} \mathrm{~m}\) (b) \(10^{-6} \mathrm{~m}\) to \(10^{-3} \mathrm{~m}\) (c) \(10^{-12} \mathrm{~m}\) to \(10^{-9} \mathrm{~m}\) (d) \(10^{-3} \mathrm{~m}\) to \(10^{-6} \mathrm{~m}\)

Step-by-Step Solution

Answer

The diameter of colloidal particles ranges from \(10^{-9} m\) to \(10^{-6} m\). Answer: (a)

Step 1: Understand the Properties of Colloidal Particles

Colloids are mixtures where one substance is dispersed evenly throughout another. The size of the particles in a colloid is crucial because it affects the stability and behavior of the colloid. Colloidal particles typically have diameters that are larger than atoms and small molecules but smaller than particles that settle out of their dispersing medium due to gravity.

Step 2: Recognize the Typical Size Range for Colloidal Particles

Colloidal particles are typically in the range from 1 nanometer (\(10^{-9} m\)) to 1000 nanometers (\(10^{-6} m\)). This size allows them to remain suspended and not settle out quickly, yet be large enough to scatter light, a phenomenon known as the Tyndall effect.

Step 3: Match the Given Ranges with the Colloidal Range

We are given four options, each with a range of diameters. Option (a) offers a range from \(10^{-9} m\) to \(10^{-6} m\), which matches exactly with the typical size range for colloidal particles. The other options either start or end outside the range of 1 nanometer to 1000 nanometers.

Step 4: Select the Correct Option

Based on the recognized size range for colloidal particles, the range in option (a) from \(10^{-9} m\) to \(10^{-6} m\) falls within the typical range for colloidal particles. Therefore, option (a) is the correct choice for the diameter of colloidal particles.

Key Concepts

Particle Size Range

Colloidal particles bridge the gap between the atomic and macroscopic worlds, occupying a unique size range that significantly influences their behavior in a mixture. These particles typically fall between 1 nanometer ( 10^{-9} m) and 1000 nanometers ( 10^{-6} m) in diameter. This range is essential because particles smaller than this range are more similar to molecular and atomic scales, while those larger tend to behave more like bulk matter. The size range of colloids allows them to remain finely dispersed within a medium, contributing to their stability and resistance to settling. Understanding this size range is vital when studying the behavior and applications of colloidal systems in various fields such as medicine, chemistry, and materials science.

• Smaller particles can move freely and remain suspended.
• Larger particles could potentially settle out due to gravity.

This size-dependent behavior is key to explaining why colloids maintain stability over time.

Tyndall Effect

The Tyndall effect is a fascinating optical phenomenon that is often used to identify colloidal mixtures. It occurs when light is scattered by particles in its path. In colloids, particles are just the right size to scatter light, thus making the light beam visible as it passes through the solution.
This effect is useful in distinguishing colloids from true solutions, as true solutions do not scatter light due to the much smaller size of their constituent particles.

• Colloids will display the Tyndall effect, making the light beam visible.
• True solutions, such as salt water, will not scatter light and thus, the light beam remains invisible.

When you shine a flashlight through a colloidal solution like fog or milk, you'll see the path of light, thanks to the Tyndall effect. Understanding this effect not only aids in identifying colloids but also in studying their properties and behaviors.

Properties of Colloids

Colloids possess unique properties that differentiate them from other mixtures such as solutions or suspensions. These properties arise from the specific characteristics of the dispersed particles and their interactions with the medium. Here are some key properties of colloids:

• Heterogeneity: Though uniform in appearance, colloids contain two phases: the dispersed phase and the continuous phase.
• Brownian Motion: Microscopically, particles exhibit random movement, preventing them from settling.
• Adsorption: Colloidal particles can adsorb ions, stabilizing the colloid through charge repulsions.
• Electrophoresis: Colloidal particles can migrate in an electric field, due to their charge.

These properties are explored for applications ranging from industrial processes to biomedicine, each leveraging the distinctive behaviors of colloidal particles.

Suspension Stability

The stability of a suspension refers to its ability to remain in a dispersed state without the particles settling out over time. Colloidal stability is a vital concept because it determines the functional quality and shelf life of a colloidal system. Several factors contribute to the stability of colloids:

• Particle Size: Smaller particles enhance stability due to less gravitational pull.
• Charge: Like-charged particles repel each other, preventing aggregation.
• Brownian Motion: Keeps particles in motion, preventing them from settling.

In practical terms, substances such as milk maintain their uniformity, thanks to stabilizing factors that prevent the cream from separating. Understanding suspension stability is essential for industries where colloids play a crucial role, such as food products, pharmaceuticals, and cosmetics.