Question

The method usually employed for the destruction of a colloidal solution is: (a) dialysis (b) addition of electrolytes (c) diffusion through animal membrane (d) condensation

Short answer

The method usually employed for the destruction of a colloidal solution is the addition of electrolytes.

Step-by-step solution

Understanding Colloidal Solutions

A colloidal solution is a heterogeneous mixture where one substance (dispersed phase) is dispersed uniformly throughout another substance (dispersion medium). These solutions are stable due to the charge on colloidal particles.

Understanding the Destruction of Colloidal Solutions

Destruction of a colloidal solution, also known as coagulation or precipitation, involves aggregating the colloidal particles so that they no longer remain dispersed and settle out of the mixture.

Identify the Correct Method

The addition of electrolytes to a colloidal solution causes the neutralization of the charge on colloidal particles, leading to coagulation. Hence, electrolytes can destroy colloidal solutions by precipitating the colloidal particles.

Key concepts

Colloidal Solution

A colloidal solution is a kind of mixture where tiny particles, known as the dispersed phase, are spread out within a medium called the dispersion medium. These particles are larger than individual molecules but too small to settle out under the influence of gravity, which is why milk looks evenly white and why the sky appears blue. Colloids can be solid, liquid, or gas, but they always have two phases; for example, aerosol sprays are a colloidal system with liquid dispersed in gas.

One of the fascinating characteristics of colloidal solutions is the Brownian motion. This is the random, erratic movement of colloidal particles, which prevents them from settling due to gravity. Additionally, these particles often carry an electrical charge, which keeps them repelling each other and remains evenly distributed throughout the dispersion medium.

Coagulation

Coagulation is the process that leads to the transformation of a colloidal solution into a coarser aggregation of particles, which ultimately settle out or form a precipitate. This typically happens when the stabilizing forces holding the colloids apart are neutralized or overcome. You can think of coagulation like a dance party where all the particles are happily dancing around in the solution, but suddenly, the music stops (the charge is neutralized), and everyone clumps together.

There are several ways to induce coagulation, such as heating or adding certain chemicals. In some situations, even shaking or stirring vigorously can cause colloids to coagulate. The key to this process is to disrupt the balance of forces that keep colloidal particles separate and stable.

Electrolytes in Colloids

Colloids are usually electrically charged, and this charge is crucial for their stability. Electrolytes, which are substances that dissociate into ions in solution, can affect colloidal solutions significantly. When electrolytes are added to a colloidal solution, their ions can neutralize the charge on colloidal particles.

This neutralization lessens the repulsive forces between particles, allowing them to come closer and clump together – initiating the coagulation process. It's similar to having magnets with opposite poles: when the right opposites meet, they stick together. Electrolytes that have ions with a charge opposite to that of the colloidal particles are particularly effective in causing coagulation. The amount of electrolyte needed to coagulate a colloidal solution can be used to measure the charge on the colloidal particles.

Physical Chemistry JEE

Colloids play a critical role in physical chemistry, especially for students preparing for competitive exams like the Joint Entrance Examination (JEE) for engineering in India. Understanding colloidal properties, how they interact with different chemicals, and the principles of coagulation are important for JEE aspirants.

The topic covers a wide range of applications, from the food industry to medicinal drugs, and has implications in understanding natural phenomena. Concepts such as the Tyndall effect, which involves the scattering of light by colloidal particles, and the impact of electrolytes on the stability of colloidal solutions, are frequently tested in JEE. These topics require not only a strong grasp of fundamental physical chemistry principles but also the ability to apply them to solve complex problems, which is a common task on the JEE.