Problem 158 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following statements are correct? (a) Presence of equal and similar charges on colloidal particles provides stability to the colloids (b) Mixing two oppositely chartged sols neutralises their charges and stabilises the colloid. (c) Brownian movement stabilises sols (d) Any amount of dispersed liquid can be added to emulsion without destabilising it.

Step-by-Step Solution

Answer

Statements (a) and (c) are correct.

Step 1: Understanding the Question

We are asked to evaluate four statements regarding colloids to determine which are correct. We'll analyze each statement individually.

Step 2: Analyzing Statement (a)

Statement (a) asserts that the presence of equal and similar charges on colloidal particles provides stability to the colloids. This is accurate because particles with similar charges repel each other, preventing aggregation, thus keeping the colloid stable.

Step 3: Analyzing Statement (b)

Statement (b) claims that mixing two oppositely charged sols would neutralize their charges and stabilize the colloid. This is incorrect because neutralizing the charges can lead to aggregation of particles, thus destabilizing the colloid.

Step 4: Analyzing Statement (c)

Statement (c) suggests that Brownian movement stabilizes sols. This is correct because the random movement helps keep the particles suspended and prevents them from settling.

Step 5: Analyzing Statement (d)

Statement (d) states that any amount of dispersed liquid can be added to an emulsion without destabilizing it. This is incorrect; adding too much dispersed liquid can disrupt the emulsion, leading to phase separation.

Step 6: Conclusion

The correct statements are (a), which refers to charge stability, and (c), dealing with the Brownian movement.

Key Concepts

Stability of Colloids

Colloids are fascinating mixtures where tiny particles are dispersed throughout another substance. Their stability is crucial for maintaining their unique characteristics, and this primarily hinges on the presence of similar and equal charges on the colloidal particles.

• These like charges cause repulsion among particles, ensuring they do not clump together.
• The repulsive forces help maintain a uniform distribution of particles throughout the colloid.
• Without this repulsion, particles would aggregate, leading to the settling of the dispersed phase, thus destabilizing the colloid.

Additionally, other factors like the presence of a stabilizing layer or the use of emulsifiers can also enhance the stability of colloids. However, the primary mechanism for most systems is the electrostatic repulsion due to similar charges.

Brownian Movement

Brownian movement is a fascinating phenomenon observed in colloidal systems, where particles exhibit random, erratic movement. This motion arises due to collisions with the molecules of the dispersion medium.

• The constant jostling and zigzagging around prevent the particles from settling at the bottom.
• It effectively helps keep the particles suspended in the medium, contributing to the stability of the colloid.
• Without Brownian movement, gravity would eventually lead to sedimentation of particles.

Brownian movement is particularly significant for smaller particles, as their random motion is more pronounced. This inherent feature is crucial in maintaining the homogeneity and stability of colloidal solutions.

Charged Sols

Charged sols are colloids where the dispersed particles carry an electrical charge, which plays a critical role in their stability.

• The charge on sols arises due to different mechanisms: adsorption of ions, ionization of groups, or electrical double layer formation.
• This charge ensures that particles repel one another, hindering aggregation and promoting stability.
• In cases where two oppositely charged sols are mixed, their charges can neutralize. This can cause particles to clump together, destabilizing the colloid, contrary to simplifying beliefs.

Understanding the nature of these charges and their interactions is vital, especially in industrial applications where precise control over stability is required. Charged sols exemplify how electrical character can influence colloidal behavior profoundly, making them a key subject in colloid chemistry.