Question

Gold number is measure of (a) amount of gold present in colloidal solution (b) amount of gold required to break the colloid (c) amount of gold required to protect the colloidal (d) none

Short answer

The correct answer is (c) amount of gold required to protect the colloidal.

Step-by-step solution

Identify the Meaning of the Term 'Gold Number'

The 'gold number' is a property specific to colloidal solutions. It's a measure of the protective power of a lyophilic colloid against the coagulating action of electrolytes. Simply put, it quantifies the colloidal stability granted by certain substances, i.e., how much of a certain substance is required to prevent the precipitation of a colloidal solution upon the addition of a specific amount of an electrolyte.

Match the Definition to the Options

With the definition at hand, we must look at the available options and determine which matches best. Analyze each option separately and compare it with the definition of the gold number.

Choose the Correct Option

By definition, the 'gold number' is neither the amount of gold present in the colloidal solution (option a), nor is it the amount of gold required to break the colloid (option b). It is, in fact, the amount of a protective substance that is required to prevent the precipitation of a colloidal solution (option c). Thus, option (c) is the correct answer.

Key concepts

Colloidal Stability

Colloidal stability is a key concept in understanding how colloids behave and maintain their dispersed state. Colloids are mixtures where tiny particles are dispersed throughout another substance.
A stable colloidal solution retains its dispersion and resists aggregation or settling over time.
Electrolytes can cause coagulation, clumping the colloidal particles. ### Factors Affecting Colloidal Stability To achieve stability in colloidal solutions, we can consider:

• Steric Stabilization: This involves long-chain molecules adsorbing on colloidal particles, preventing close contact.
• Electrostatic Stabilization: Colloids with charges repel each other, maintaining dispersion. Adding electrolytes can disturb these charges, leading to coagulation.
• Gold Number: It helps measure how much stabilizing agent is needed against coagulation, assessing the colloid's stability.

Maintaining colloidal stability is crucial in various industrial and biological processes, making the understanding of each of these factors essential.

Lyophilic Colloids

Lyophilic colloids, also known as solvent-loving colloids, are quite intriguing in the way they interact with the dispersing medium.
These colloids have a strong affinity for the solvent, leading to excellent dispersibility.
Substances like starch or gelatin form lyophilic colloids. ### Characteristics of Lyophilic Colloids Lyophilic colloids exhibit unique properties:

• Reversibility: They can be dried and redispersed in the solvent without losing properties.
• Viscoelasticity: These dispersions are often viscous and can exhibit elastic behavior.
• Stability: They are highly stable and require high concentrations of electrolytes to coagulate, which is why they are known to protect lyophobic colloids from coagulating.

Lyophilic colloids are widely used in food, cosmetics, and pharmaceuticals for their stabilizing properties.

Coagulation

Coagulation refers to the process where particles in a colloidal solution cluster together, eventually leading to precipitation or settling out of the suspension.
It's a critical point of discussion when studying colloidal systems. ### Mechanisms of Coagulation There are various paths through which coagulation can occur, including:

• Neutralization of Charge: Adding electrolytes can neutralize the charge on colloidal particles, diminishing the repulsive forces and enhancing attraction, leading to coagulation.
• Bridging: Particles can form bridges with the help of multivalent ions or polymers, bringing them together.
• Dehydration: Removal of the solvated layer around particles results in closer contact and aggregation.

Understanding coagulation is critical for processes like water treatment, where the removal of suspended particles is necessary for clear water.