Question

Select the properties which are for lyophilic colloidal sols: (a) viscosity same as that of the medium (b) extensive hydration takes place (c) particles migrate either towards cathode or anode in an electric field (d) particle cannot be detected even under ultramicroscope

Short answer

The properties for lyophilic colloidal sols are: (b) extensive hydration takes place, (c) particles migrate either towards cathode or anode in an electric field. Property (a) is incorrect because lyophilic sols generally have higher viscosity, and (d) is incorrect as particles can be seen under an ultramicroscope.

Step-by-step solution

- Understanding Lyophilic Colloids and Viscosity

Recognize that lyophilic colloidal sols have an affinity for the dispersion medium, and because of this, the viscosity of the sol is often higher than that of the medium due to the interaction between the dispersed phase and the dispersion medium.

- Analyzing Hydration in Lyophilic Colloids

Determine the extent of hydration for lyophilic colloids. These colloids exhibit extensive hydration where the dispersed particles are heavily solvated, contributing to stability.

- Evaluating the Electrophoretic Migration

Examine if particles in lyophilic colloids migrate in an electric field. Generally, particles in colloidal solutions migrate due to their charge, either towards the anode if negatively charged or towards the cathode if positively charged.

- Checking for Particle Detection

Consider whether particles can be detected under an ultramicroscope. In lyophilic colloidal sols, particles are large enough to be detected under an ultramicroscope, contrary to true solutions where individual molecules cannot be seen.

Key concepts

Colloid Chemistry

Colloid chemistry explores the science of colloidal particles - substances that are microscopically dispersed evenly throughout another substance. Colloids are neither true solution nor suspension, and they display unique properties that distinguish them from these other mixtures. A familiar property is the Tyndall effect, where light scatters as it passes through a colloidal solution.

Lyophilic colloidal sols are a type of colloid where the dispersed substance has a natural affinity for the solvent, often leading to increased stability and some unique behaviors including significant hydration and altered viscosity. In these sols, particles have substantial interactions with the surrounding medium, typically a liquid, resulting in a solution that resists separation.

Electrophoretic Migration

Electrophoretic migration is a phenomenon observed in colloidal solutions, where colloidal particles move under the influence of an electric field. This movement is a result of the surface charge on colloidal particles which could be either positive or negative, causing them to migrate towards the electrode with the opposite charge - anode or cathode respectively.

This behavior plays a crucial role in methods used for characterizing colloids and for applications such as electrophoresis, a technique used to separate different molecules based on their size and charge. The direction and velocity of the movement can provide valuable information about the nature of the colloidal particles in terms of their surface charge and the potential they generate in a solution.

Hydration in Colloids

Hydration in colloids, especially lyophilic sols, is significant due to the affinity the dispersed particles have for water molecules. This process involves the attachment of water molecules to the surface of colloidal particles, leading to a hydration shell or layer.

The extent of this hydration greatly influences the properties of the colloid, such as its stability, because the hydrated layer provides a barrier that discourages particle aggregation. The more extensive the hydration, the greater the stability and viscosity of the sol. This is a key aspect that contributes to the unique behavior and characteristics of lyophilic colloids.

Viscosity of Colloidal Solutions

Viscosity is a measure of a fluid's resistance to flow and is an important factor in colloidal chemistry. The viscosity of colloidal solutions is significantly affected by the size and concentration of colloidal particles, as well as their interaction with the solvent.

Lyophilic colloids typically exhibit a viscosity that is higher than that of the pure solvent due to the increased interactions at the molecular level. The presence of a hydrated layer around colloidal particles and the formation of a network within the solvent increase the internal resistance to flow. As a result, understanding the viscosity of lyophilic colloidal solutions is essential for applications in industries like food, pharmaceuticals, and cosmetics, where texture and stability are paramount.