Properties of Colloidal Solutions Video Lecture - Chemistry Class 12 - NEET

Ans. Colloidal solutions have several properties that distinguish them from other types of solutions. Some of these properties include: - Opalescence: Colloidal solutions exhibit a characteristic opalescent appearance due to the scattering of light by the dispersed particles. - Brownian motion: The dispersed particles in a colloidal solution undergo constant random motion, known as Brownian motion, due to collisions with the surrounding solvent molecules. - Stability: Colloidal solutions are typically stable and do not settle over time. This is due to the repulsive forces between the dispersed particles, which prevent aggregation and precipitation. - Tyndall effect: When a beam of light is passed through a colloidal solution, it scatters the light, making the path of the beam visible. This phenomenon is known as the Tyndall effect and is used to distinguish colloidal solutions from true solutions. - Particle size: The particles in a colloidal solution are larger than those in true solutions but smaller than those in suspensions. They have a size range of 1-1000 nanometers.

Ans. Opalescence in colloidal solutions occurs due to the scattering of light by the dispersed particles. When a beam of light passes through a colloidal solution, the particles scatter the light in different directions, causing it to appear cloudy or opalescent. This scattering of light is a result of the interaction between the incident light and the particles, which causes deviations in the light's path. The wavelength of the incident light is similar to the size range of the dispersed particles, leading to constructive interference and the appearance of opalescence.

Ans. Colloidal solutions exhibit Brownian motion because of the constant random motion of the dispersed particles. Brownian motion occurs due to collisions between the particles and the surrounding solvent molecules. These collisions cause the particles to move in a zigzag pattern, resulting in their dispersion throughout the solution. The motion is driven by the thermal energy of the solvent molecules and is essential for maintaining the stability of colloidal solutions by preventing the particles from settling.

Ans. Repulsive forces play a crucial role in the stability of colloidal solutions. These forces arise from the interaction between the dispersed particles and can be either electrostatic or steric in nature. Electrostatic repulsion occurs when the particles have an electric charge of the same sign, causing them to repel each other. Steric repulsion, on the other hand, arises from the presence of adsorbed layers of molecules or polymers around the particles, which create a barrier preventing them from coming into close contact. The repulsive forces counteract the attractive forces between the particles, such as van der Waals forces, and prevent their aggregation and precipitation. This leads to the long-term stability of colloidal solutions, as the particles remain dispersed and do not settle over time.

Ans. The Tyndall effect can be used to distinguish colloidal solutions from true solutions. When a beam of light is passed through a colloidal solution, the dispersed particles scatter the light, making the path of the beam visible. This scattering of light is not observed in true solutions, where the particles are too small and do not scatter light significantly. By observing the presence of the Tyndall effect, one can determine whether a solution is colloidal or true. If the path of the light beam is clearly visible and exhibits a scattered appearance, it indicates the presence of dispersed particles and confirms that the solution is colloidal. On the other hand, if the light passes through the solution without scattering, it suggests that the solution does not contain dispersed particles and is a true solution.