Question

Which of the following colloids cannot be coagulaten easily? (a) Reversible colloids (b) Lyophillic colloids (c) Irreversible colloids (d) Lyophobic colloids

Short answer

Lyophillic (reversible) colloids cannot be coagulated easily.

Step-by-step solution

Understanding Colloids

Colloids are mixtures where particles of one substance are dispersed in another. They can be categorized into lyophilic, lyophobic, reversible, and irreversible colloids based on their affinity to the medium and their stability.

Defining Key Terms

Lyophilic colloids (also known as reversible colloids) are those where the dispersed phase has a strong affinity for the dispersion medium, making them stable and reversible upon mixing.

Analyzing Lyophobic Colloids

Lyophobic colloids have little to no affinity for the dispersion medium, making them less stable and more easily coagulated. They are also known as irreversible colloids.

Comparing Stability

The stability of colloids depends on the interaction between the dispersed phase and the medium. Lyophilic (reversible) colloids are more stable because of the strong attraction, while lyophobic colloids are less stable due to weaker interactions.

Identifying the Correct Answer

Given the stability of lyophilic colloids due to their strong affinity for the medium, lyophilic colloids (reversible colloids) cannot be coagulated easily, unlike lyophobic colloids which are easily coagulated.

Key concepts

Lyophilic Colloids

Lyophilic colloids, also known as "solvent-loving" colloids, are formed when the particles of the dispersed phase have a strong affinity towards the dispersion medium. This attraction is so strong that these colloids are stable and can easily be remixed if separated. The stability comes from the natural affinity between the solvent and the particles. This is why, in many cases, the formation of a lyophilic colloid is spontaneous.
Such colloids are often also referred to as "reversible colloids" both due to their ability to mix easily again after separation and their responsiveness to solvation.

• Example: Gelatin, starch in water, and rubber in benzene are common examples of lyophilic colloids.
• Stability: These colloids are highly stable because once dissolved, they do not settle or precipitate easily.
• Coagulation: They require very high amounts of electrolytes to coagulate due to their strong interaction with the dispersion medium.

Lyophobic Colloids

On the other hand, we have lyophobic colloids, known as "solvent-hating" colloids. These colloids show very little to no affinity for the dispersion medium. Due to this lack of attraction, they are less stable and are not formed spontaneously. Rather, they require external energy input or mechanical processes like shaking or stirring to be formed.
They are referred to as "irreversible colloids" because once they are precipitated, they cannot be remixed simply by shaking or stirring.

• Example: Gold, silver, and sulfur colloids.
• Stability: These colloids are considered unstable compared to lyophilic colloids.
• Coagulation: They coagulate easily with the addition of small amounts of electrolytes because of weak interactions with the medium.

Coagulation of Colloids

Coagulation refers to the process of precipitating out the dispersed particles from a colloid. This is usually achieved by the addition of electrolytes, changing temperature, or altering the pH.
Understanding this process is key to manipulating colloidal systems in practical applications. Whether the colloids are lyophilic or lyophobic depends on the ease with which they can be coagulated.

• Lyophilic Colloids: These require a high concentration of electrolytes to induce coagulation due to their stability.
• Lyophobic Colloids: They can be easily coagulated with a small amount of electrolyte due to their low stability.
• Coagulation is often used in industries such as water purification, medicine, and food science to separate or remove unwanted particles.

Overall, the tendency to coagulate is fundamentally tied to the colloid's affinity for its medium, dictating its stability and behavior in various environments.