Question

Explain how each of the following factors helps determine the stability or instability of a colloidal dispersion: (a) particulate mass, (b) hydrophobic character, (c) charges on colloidal particles.

Short answer

The stability of colloidal dispersions is determined by (a) particulate mass, in which smaller particles with lower mass have better stability; (b) hydrophobic character, where particles with a low hydrophobic character are well-dispersed and stable in water; (c) charges on colloidal particles, as similar charges repel each other, preventing aggregation and maintaining stability, while opposite or no charges promote aggregation and instability.

Step-by-step solution

(a) Particulate Mass

Particulate mass refers to the size and weight of the colloidal particles. Greater mass, or larger particles, can cause the particles to settle more quickly due to gravitational forces, leading to instability in the colloidal dispersion. Smaller particles with lower mass are less affected by gravity and can remain suspended for longer periods, contributing to better stability.

(b) Hydrophobic Character

The hydrophobic character of the colloidal particles refers to their tendency to repel water. If the particles have a high hydrophobic character, they will tend to be poorly dispersed in an aqueous medium, leading to agglomeration and hence, instability. Conversely, particles with low hydrophobic character tend to be better dispersed in water, promoting stability of the colloidal dispersion.

(c) Charges on Colloidal Particles

The charges present on the surface of colloidal particles can greatly influence the stability of the dispersion. Generally, particles with similar charges repel each other, preventing them from aggregating and maintaining the stability of the dispersion. Whereas, if the particles have no charge or opposite charges, they are likely to come together and form larger aggregates, causing instability in the colloidal dispersion. The presence of charged particles or adsorbed ions can therefore create a stabilizing effect on colloidal dispersions.

Key concepts

Particulate Mass

The mass of colloidal particles plays a crucial role in determining the stability of colloidal dispersions. Heavier particles, due to their greater mass, are subject to more significant gravitational forces. This means they tend to settle more quickly out of the dispersion, leading to instability.
When particles settle, the distribution of particles in the medium becomes uneven, causing them to aggregate or form sediment, which is undesirable for colloidal stability. Conversely, smaller particles, those with less mass, can resist settling due to gravity.
They remain suspended in the dispersion for extended periods, contributing to a more stable dispersion. A stable colloid ensures that the particles are evenly distributed, which can be critical in various applications, from pharmaceuticals to food products.

• Heavier particles settle quickly, leading to instability.
• Smaller particles resist gravity better, improving stability.
• Stable colloids have consistent particle distribution.

Hydrophobic Interaction

Hydrophobic interaction is a factor that influences whether colloidal particles will be dispersed in a medium like water. Hydrophobic particles repel water, leading them to cluster together, which is known as agglomeration.
This clustering results in particles coming out of the dispersion, causing instability. In contrast, if particles have a low hydrophobic character, they interact more favorably with water, resulting in better dispersion and stability.
Hydrophilic particles, those that attract water, are often better at staying evenly dispersed, reducing the risk of agglomeration.

• Hydrophobic particles repel water, causing instability.
• Hydrophilic particles mix well with water, enhancing stability.
• Effective dispersion reduces agglomeration risk.

Surface Charge

The surface charge on colloidal particles is integral to maintaining stability in a dispersion. Charged particles naturally repel each other due to electric forces, which prevents them from coming too close and clumping together.
This repulsion helps maintain an even distribution of particles, enhancing stability. However, if particles lack a significant charge, or possess opposite charges, they tend to attract each other.
This attraction can lead to aggregation, where particles form larger clusters, leading to a breakdown in stability. Ensuring particles have a similar charge can create an effective barrier to agglomeration.

• Similar charges cause repulsion, supporting stability.
• No or opposite charges lead to attraction, causing instability.
• Charge maintenance is crucial for preventing aggregation.