Problem 195 - A Complete Resource Book in Chemistry for JEE Main

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

Step-by-Step Solution

Answer

The order is (d) \(\mathrm{Na}^{+}<\mathrm{Ba}^{2+}<\mathrm{Al}^{3+}\).

Step 1: Identify the Principles Involved

The coagulating power of ions is governed by the Hardy-Schulze rule, which states that the greater the charge on an ion, the greater its ability to cause coagulation of a sol. This implies that the coagulating power is proportional to the charge of the ion.

Step 2: Assign Charges to Ions

Identify the charge on each ion: - \(\mathrm{Na}^{+}\) has a charge of +1.- \(\mathrm{Ba}^{2+}\) has a charge of +2.- \(\mathrm{Al}^{3+}\) has a charge of +3.

Step 3: Compare Ion Charges to Determine Coagulating Power

Based on the Hardy-Schulze rule, the ion with the highest charge will have the greatest coagulating power. Therefore:- \(\mathrm{Al}^{3+}\) with a charge of +3 has the highest coagulating power.- \(\mathrm{Ba}^{2+}\) with a charge of +2 comes next.- \(\mathrm{Na}^{+}\) with a charge of +1 has the lowest coagulating power.

Step 4: Arrange Ions in Increasing Order of Coagulating Power

Arranging the ions in order of increasing coagulating power based on their charges, we get:\[\mathrm{Na}^{+} < \mathrm{Ba}^{2+} < \mathrm{Al}^{3+}\]

Key Concepts

Hardy-Schulze rule

The Hardy-Schulze rule is crucial for understanding how different ions affect the coagulation of colloidal solutions. This rule indicates that the higher the charge on an ion, the greater its ability to coagulate, or "clump together," in a colloid. This is because ions with higher charges exert a stronger electrostatic force, which can neutralize the charged particles in a colloid.
For instance, if you have a sol with negatively charged particles, adding positively charged ions with a high charge, like \( ext{Al}^{3+} \), can lead to stronger coagulation. The positive ions attempt to balance out the charge by sticking to negatively charged colloidal particles, reducing their ability to repel each other and thus facilitating coagulation.
Understanding this principle helps you predict and control the stability of colloids in various applications such as medicine, food production, and environmental science.

ion charge and coagulation

Ion charge plays a vital role in the coagulation process of colloids. Each ion carries a specific charge, which directly affects its ability to contribute to coagulation based on the Hardy-Schulze rule. In our example, we considered ions like \( \text{Na}^{+} \), \( \text{Ba}^{2+} \), and \( \text{Al}^{3+} \).

• \( \text{Na}^{+} \) has a charge of +1, giving it the least coagulating power.
• \( \text{Ba}^{2+} \), with its higher charge of +2, has a more significant coagulating effect.
• \( \text{Al}^{3+} \), with the highest charge of +3, exhibits the greatest ability to coagulate a sol.

These varying charges result in different levels of electrostatic attraction between the ions and the colloidal particles. As the charge increases, so does the ability of the ion to neutralize the charge on colloidal particles, leading to stronger coagulation. As such, ion charge is a fundamental aspect to consider when manipulating the stability and behavior of colloidal solutions.

arsenic sulphide sol coagulation

Arsenic sulphide sol is a type of colloidal system sensitive to coagulation by electrolytes. Its particles are negatively charged, making them react more significantly with positive ions. When studying the arsenic sulphide sol, understanding which electrolytes cause coagulation is essential.
The electrolytes contain ions like \( \text{Na}^{+} \), \( \text{Ba}^{2+} \), and \( \text{Al}^{3+} \). According to the Hardy-Schulze rule, the coagulating power increases with the ion's charge. Therefore:

• \( \text{Na}^{+} \) causes the least coagulation due to its +1 charge.
• \( \text{Ba}^{2+} \) provides a greater coagulating effect because of its +2 charge.
• \( \text{Al}^{3+} \) offers the highest coagulating power with its +3 charge.

In practical terms, this means if you want to destabilize the arsenic sulphide sol efficiently, using \( \text{Al}^{3+} \) would be the most effective approach due to its high charge. This principle aids in diverse applications such as water purification and the recovery of materials in industrial processes.