Problem 112 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following statements are correct? (1) Electro-osmsis is the movement of the particles of dispersion medium under the influence of an electric field. (2) On the application of an electric field, the particles of a lyophobic sol may move in either direction or not move at all. (3) Surface tension of lyophobic sols is similar to that of the dispersion medium. (a) 1 and 2 (b) 1 and 3 (c) 2 and 3 (d) 1,2 and 3

Step-by-Step Solution

Answer

The correct statements are 2 only, none of the given options match exactly.

Step 1: Understand the concept of Electro-osmosis

Electro-osmosis refers to the movement of a liquid or the dispersion medium through a porous material or across a charged surface under the influence of an electric field. Therefore, statement (1) is incorrect because it describes the movement of particles in the dispersion medium, not the medium itself.

Step 2: Analyze the effect of an electric field on lyophobic sols

Lyophobic sols are colloidal solutions where the dispersed phase does not interact favorably with the dispersion medium. When an electric field is applied to such sols, the particles can move in either direction (to the anode or cathode) or may not move at all, depending on their charge. Thus, statement (2) is correct.

Step 3: Evaluate surface tension in lyophobic sols

In lyophobic sols, the surface tension of the dispersed phase is usually not similar to that of the dispersion medium. This is because lyophobic sols, by definition, exhibit poor interactions with the dispersion medium, leading to differences in surface tensions. Therefore, statement (3) is incorrect.

Key Concepts

Lyophobic sol

Lyophobic sols are a type of colloidal solution where the dispersed particles do not have a strong affinity for the solvent or dispersion medium. This lack of interaction is primarily because of the non-favorable forces between the particles and the medium. Consequently, these sols are often less stable and might be more prone to coagulation or settling.

Important characteristics of lyophobic sols include:

• Weak stability due to the absence of solvent attraction.
• Higher susceptibility to coagulation, serving as critical factors in their behavior under various conditions.
• The need for stabilizing agents to maintain the sol's properties.

Understanding the nature of lyophobic sols is vital when studying their behavior, especially under the influence of external factors like electric fields.

Colloidal solutions

Colloidal solutions, or colloids, are mixtures where one substance is dispersed evenly throughout another. These systems have unique properties because the size of the dispersed particles is intermediate between that of a true solution and a suspension.

Key points about colloidal solutions:

• The particles are typically in the range of 1 to 1000 nanometers.
• They exhibit the Tyndall effect, which is the scattering of light by colloidal particles.
• Colloidal solutions can be classified as lyophobic or lyophilic, depending on the interaction between the dispersed phase and the dispersion medium.

The interactions in colloidal systems are fundamental to understanding how they behave under various physical and chemical conditions.

Surface tension

Surface tension is a physical property that represents the amount of energy or force required to increase the surface area of a liquid. It is an essential factor in many phenomena that involve liquid surfaces, such as the formation of drops and bubbles.

For lyophobic sols:

• The surface tension is typically different from the dispersion medium due to the weak interaction between particles and the medium.
• This variation is a direct consequence of the nature of lyophobic interactions, where the dispersing medium does not "wet" the particles efficiently.
• The difference in surface tension can affect the stability and behavior of the colloidal solution.

Understanding surface tension in colloidal systems is crucial for manipulating and predicting the behavior of such systems in practical applications.

Electric field effect on colloids

The application of an electric field to colloidal solutions can significantly influence the behavior of the dispersed particles. This phenomenon is known as electrophoresis, where charged particles move towards the electrode of opposite charge.

In the context of lyophobic sols:

• The movement of particles can vary; they may move towards the anode or cathode, or sometimes not move, depending on their charge and the nature of the sol.
• Electrophoretic mobility is a crucial parameter, affecting how particles mobilize under an electric field.
• This effect is utilized in various technological and industrial processes, such as separation techniques and measuring zeta potential.

Examining these effects is essential for applications that rely on the precise manipulation of colloidal systems under electric fields.