Question

Freshly prepared precipitate sometimes gets converted to colloidal solution by (a) Electrolysis (b) Coagulation (c) Peptisation (d) Diffusion

Short answer

Peptisation (c) converts a precipitate into a colloidal solution.

Step-by-step solution

Understanding the Terms

First, let's understand what each of the terms in the options means: - **Electrolysis**: A process that uses electricity to split chemical compounds, usually to separate elements. - **Coagulation**: The process where colloidal particles come together to form a precipitate. - **Peptisation**: The process of converting a precipitate into a colloidal solution by adding an appropriate electrolyte. - **Diffusion**: The movement of particles from an area of higher concentration to an area of lower concentration, which does not form or convert precipitates.

Identifying the Correct Process

Given that the task is to convert a freshly prepared precipitate into a colloidal solution, consider which process accomplishes this. - **Electrolysis** does not play a role in forming colloidal solutions from precipitates. - **Coagulation** is the opposite process; it actually converts a colloidal solution into a precipitate. - **Peptisation** specifically refers to using an electrolyte to convert a precipitate into a colloidal solution. - **Diffusion** does not contribute to the conversion of precipitate to a colloidal solution.

Selection of the Answer

Based on the understanding of the processes, **peptisation** is the only process where a precipitate is converted into a colloidal solution by using an electrolyte. Therefore, option (c) peptisation is the correct answer.

Key concepts

Peptisation

Peptisation is a process pivotal in colloidal chemistry, and it involves converting a precipitate into a colloidal solution. This conversion happens through the addition of an electrolyte, which helps disperse the precipitate's particles throughout a solvent.

When an electrolyte is added, its ions are adsorbed onto the surface of the precipitate particles. This adsorption reduces the attractive forces between particles, enhancing their stability and preventing them from clumping together. Instead, they become evenly distributed, resulting in a colloidal solution.

Peptisation is crucial in the formation of stable colloids, widely used in industries like pharmaceuticals and food production. It ensures the dispersion of active ingredients, enhancing the product's efficacy and consistency. Without peptisation, many colloids would remain as inactive precipitates.

Coagulation

Coagulation is essentially the opposite of peptisation. It refers to the process where colloidal particles aggregate together to form a precipitate.

Coagulation usually occurs when an electrolyte is added to a colloidal solution. The ions in the electrolyte neutralize the charge on the colloidal particles, reducing their repulsion and allowing them to collide and join together. This results in the formation of larger particles that eventually settle out of the solution as a precipitate.

In practical applications, coagulation is critical in water treatment processes, where removing suspended impurities is necessary. By promoting coagulation, impurities and other particulate matter can be effectively extracted from water.

Colloidal Solution

A colloidal solution is a heterogeneous mixture where one substance (the dispersed phase) is finely distributed within another (the continuous phase).

These solutions are neither true solutions nor suspensions. The particles in a colloidal solution are typically in the range of 1 nm to 1 micrometer. This unique size range allows colloids to remain indefinitely suspended within the medium, without settling out or aggregating into larger particles.

Colloidal solutions exhibit special properties like Tyndall effect, where light scatters when passing through the mixture. They are important in various fields, including medicine and material science, for forming products like gels, emulsions, and aerosols.

Electrolysis

Electrolysis is a chemical process that uses electrical energy to drive a non-spontaneous reaction. By applying an electric current, it causes the chemical decomposition of compounds into pure elements.

In an electrolytic cell, when an electric current is passed, positive ions move toward the cathode, and negative ions move toward the anode, splitting compounds into their respective elements. Electrolysis is not involved in converting precipitates into colloidal solutions but is essential in processes like electroplating and electrorefining.

Its significant industrial applications include the extraction of metals such as aluminum and copper, as well as in producing gases like hydrogen and oxygen.

Diffusion

Diffusion is a fundamental natural process where particles spontaneously move from a region of high concentration to one of lower concentration. This movement continues until equilibrium is achieved.

Diffusion does not involve any energy input and is driven by the kinetic energy of particles. This process is crucial in biological systems for nutrient and gas exchange within cells.

In colloidal chemistry, while diffusion is always occurring on a small scale, it doesn't lead to coagulation or peptisation. Instead, diffusion helps in the uniform distribution of particles throughout the colloidal system, maintaining stability and ensuring the evenness of concentration throughout the medium.