Problem 30 - Advanced Problems in Physical Chemistry for Competitive Examinations

Question

The correct match is $$ \begin{array}{ll} \hline \text { Column I } & \text { Column II } \\ \hline \text { (1) Coagulation } & \text { (P) } \begin{array}{l} \text { Scattering of } \\ \text { light } \end{array} \\ \text { (2) Peptization } & \text { (Q) } \begin{array}{l} \text { Purification } \\ \text { of colloidal } \\ \text { solution } \end{array} \\ \begin{array}{ll} \text { (3) } \text { Tyndall } \\ \text { effect } \end{array} & \text { (R) } \begin{array}{l} \text { Addition of an } \\ \text { electrolyte } \end{array} \\ \text { (4) Dialysis } & \text { (S) } \begin{array}{l} \text { Precipitation } \\ \text { of colloidal } \\ \text { solution } \end{array} \\ \hline \end{array} $$ $$\begin{array}{llll}1 & 2 & 3 & 4\end{array}$$ (a) \(\begin{array}{llll}\mathrm{P} & \mathrm{Q} & \mathrm{R} & \mathrm{S}\end{array}\) (b) \(\begin{array}{llll}\mathrm{S} & \mathrm{R} & \mathrm{P} & \mathrm{Q}\end{array}\) (c) \(\begin{array}{llll}\mathrm{R} & \mathrm{S} & \mathrm{Q} & \mathrm{P}\end{array}\) (d) Q \(\mathrm{R} \quad \mathrm{P} \quad \mathrm{S}\)

Step-by-Step Solution

Answer

(c) R, S, P, Q

Step 1 - Understanding Coagulation

Coagulation refers to the process where colloidal particles aggregate to form a floc, usually when an electrolyte is added. So, coagulation matches with the addition of an electrolyte, which is (R).

Step 2 - Understanding Peptization

Peptization is the process of converting a precipitate into colloidal particles by adding a suitable dispersing agent. Therefore, peptization does not match with any of the given options in Column II accurately since none describes this conversion process.

Step 3 - Understanding the Tyndall Effect

The Tyndall effect is the phenomenon where light is scattered by particles in a colloid or in a very fine suspension. It matches with the scattering of light, which is (P).

Step 4 - Understanding Dialysis

Dialysis is a process for the purification of colloidal solutions, which involves removing dissolved ions by selective diffusion through a membrane. Thus, dialysis corresponds to the purification of colloidal solution, which is (Q).

Step 5 - Making the Correct Match

By analyzing each term in Column I, the correct matches are found to be:1 - Coagulation with (R)2 - Peptization does not have a direct match but it is closest to (S) as it involves colloidal solutions.3 - Tyndall effect with (P)4 - Dialysis with (Q)Option (c) matches our findings: 1 with (R), 2 with (S), 3 with (P), and 4 with (Q).

Key Concepts

Coagulation in Colloids

Coagulation in colloids is the process that involves the aggregation or clumping of fine particles into larger particles known as flocs. This typically occurs when an electrolyte is added to the colloid. The addition of the electrolyte neutralizes the charges on the colloidal particles, reducing their ability to repel each other and thus, allowing them to come together.

For example, if you're tasked with treating wastewater to remove contaminants, coagulation can be a crucial step. You would add coagulants like aluminum sulfate to bind contaminants, making them heavy enough to settle down. In understanding textbook problems surrounding coagulation, it’s imperative to recognize the role of the electrolyte and how it leads to particle aggregation.

Peptization Process

The peptization process reverses coagulation; it involves converting aggregated colloidal particles back into stable colloids, often by adding a dispersing agent. Think of it like adding soap to greasy dishes: the soap surrounds the grease and breaks it up into smaller droplets, which then disperse in the water.

When studying peptization in textbooks, one should focus on the importance of the dispersing agent and understand that without it, the precipitate would not revert to a colloidal form. This concept underscores the delicacy of balance in colloidal systems and how fine-tuned changes can switch the state of a substance.

Tyndall Effect

Have you ever noticed a beam of sunlight entering a room filled with dust and the way the light scatters in all directions? That scattering of light by the dust particles is an everyday example of the Tyndall effect. When light passes through a colloid, the particles are large enough to scatter the light, making the light path visible.

In educational settings, demonstrating the Tyndall effect can be as simple as shining a flashlight through a foggy room. By observing how colloidal particles scatter light, students can easily grasp that colloids are not solutions but suspensions with particles large enough to affect light.

Dialysis in Colloidal Purification

Dialysis in colloidal purification operates on a principle similar to how a coffee filter works. Just as the filter allows the water to pass while retaining the coffee grounds, the dialysis membrane lets small solvent molecules and ions to diffuse through, while the larger colloidal particles are retained.

During a dialysis process for purifying colloids in a laboratory exercise, one may use a membrane like cellophane. This helps in visualizing the removal of unwanted smaller particles from the colloidal solution, while ensuring the larger colloidal particles remain within the desired solution. This demonstration can exemplify why dialysis is an essential procedure for purifying colloids in both industrial and biochemical contexts.