Problem 20 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

The coagulating power of electrolytes having ions \(\mathrm{Na}^{+}, \mathrm{Al}^{3+}\) and \(\mathrm{Ba}^{2+}\) for arsenic sulphide sol increases in the order(a) \(\mathrm{Al}^{3+}<\mathrm{Ba}^{2+}<\mathrm{Na}^{+}\) (b) \(\mathrm{Na}^{+}<\mathrm{Ba}^{2+}<\mathrm{Al}^{3+}\) (c) \(\mathrm{Ba}^{2+}<\mathrm{Na}^{+}<\mathrm{Al}^{3+}\) (d) \(\mathrm{Al}^{3+}<\mathrm{Na}^{+}<\mathrm{Ba}^{2+}\)

Step-by-Step Solution

Answer

(b) \( \mathrm{Na}^{+} < \mathrm{Ba}^{2+} < \mathrm{Al}^{3+} \)

Step 1: Understanding Coagulating Power

In colloids, the coagulating power of an electrolyte is determined by the charge on its ions. The greater the charge, the higher the coagulating power. This is explained by the Hardy-Schulze rule which states that the higher the valency of the oppositely charged ion of the electrolyte added, the faster is the coagulation of the sol.

Step 2: Identifying Ion Charges

For the ions given: \( \mathrm{Na}^{+} \) has a single positive charge (+1), \( \mathrm{Ba}^{2+} \) has a charge of +2, and \( \mathrm{Al}^{3+} \) has a charge of +3.

Step 3: Applying the Hardy-Schulze Rule

According to the Hardy-Schulze rule, the coagulating power is higher for ions with higher valency. Therefore, among the given ions, \( \mathrm{Al}^{3+} \) with a +3 charge has the highest coagulating power, followed by \( \mathrm{Ba}^{2+} \) with a +2 charge, and \( \mathrm{Na}^{+} \) with a +1 charge.

Step 4: Arranging the Coagulating Powers

Based on the coagulating power determined by the ion charges, the order of the coagulating power for the ions \( \mathrm{Na}^{+}, \mathrm{Al}^{3+}, \mathrm{Ba}^{2+} \) is \( \mathrm{Na}^{+} < \mathrm{Ba}^{2+} < \mathrm{Al}^{3+} \).

Key Concepts

Hardy-Schulze Rule

The Hardy-Schulze Rule is a fundamental principle when it comes to understanding coagulation in colloidal solutions. It provides us with a simple yet powerful insight: the coagulating power of an electrolyte is primarily determined by the valency of its ions. This rule tells us that the higher the valency or the charge of the ion, the more effective it is in causing coagulation. For example, an ion with a charge of +3 will have a greater impact compared to ions with charges of +1 or +2. This increased coagulating ability is due to the stronger attraction or repulsion created by the higher charged ion. - It explains why higher valency ions are more efficient at neutralizing the charges on colloidal particles. - The rule is crucial in predicting how different ions will affect a colloidal system, guiding scientists and engineers in practical applications. Understanding this rule helps in predicting the behavior of colloidal systems when different electrolytes are introduced.

Colloids

Colloids are unique mixtures that appear homogeneous to the naked eye but are heterogeneous on the microscopic scale. These mixtures consist of a dispersed phase (particles) and a continuous phase (medium), where the particle sizes are typically between 1 and 1000 nanometers. They play a crucial role in various scientific and industrial processes and form the basis for many everyday products such as milk, fog, and paints. - Colloidal particles are often charged, which prevents them from settling or clumping together easily. - Stability of colloids can be affected by the addition of electrolytes, leading to coagulation or the eventual settling out of particles. - Understanding colloidal stability is important for both creating and maintaining products that rely on these mixtures. Colloids are fascinating because of their ability to remain suspended and their sensitivity to surface charge, which plays a critical role in their stability.

Ion Charge

Ion charge is a critical factor that influences the behavior of ions in chemical reactions and colloidal systems. The charge on an ion is determined by the loss or gain of electrons, with ions being positively or negatively charged based on this electron change.In the context of colloids and coagulation:- Ions with higher charges have greater coagulating powers. This is because they can more effectively neutralize the charges on colloidal particles, leading to faster coagulation.- For example, in the exercise, - \( \mathrm{Al}^{3+} \) has the highest charge among the ions given \((+3)\), - followed by \( \mathrm{Ba}^{2+} \) \((+2)\), - and \( \mathrm{Na}^{+} \) \((+1)\).- The stronger the charge, the more significant its effect in breaking down the colloidal solution's stability.Ion charge is a fundamental aspect in predicting and understanding the behavior of substances in various chemical scenarios.

Valency

Valency is a term used to describe the combining capacity of an element, particularly how many electrons it can gain, lose, or share to achieve a full outer shell. This concept is pivotal in understanding chemical bonding and reactions. - Valency is directly related to the ion charge, as ions form based on this combining power. - In the realm of colloids and the Hardy-Schulze rule, valency becomes incredibly important because it determines the strength of an ion's interaction with colloidal particles. - Higher valency indicates a higher ability to cause the coagulation of colloids, making valency a determining factor in applications that involve colloidal stability. A comprehensive grasp of valency enables students to predict reactions and understand the strength and implications of various ionic interactions in both simple and complex systems.