Problem 41 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following ions has the least flocculation value? (a) \(\mathrm{PO}_{4}^{3}\) (b) \(\mathrm{SO}_{4}^{2-}\) (c) \(\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]^{4}\) (d) \(\mathrm{Cl}^{-}\)

Step-by-Step Solution

Answer

Ion (c) \([\mathrm{Fe}(\mathrm{CN})_{6}]^{4-}\) has the least flocculation value.

Step 1: Understanding Flocculation

In the context of colloidal chemistry, the flocculation value of an ion is the minimum concentration of that ion needed to cause the precipitation, or coagulation, of a colloidal particle. Generally, the higher the charge of an ion, the more effectively it can cause flocculation.

Step 2: Identifying Ion Charges

Examine each ion to identify its charge. The given ions are: (a) \(\mathrm{PO}_{4}^{3-} \), which has a charge of 3-(b) \(\mathrm{SO}_{4}^{2-} \), which has a charge of 2-(c) \([\mathrm{Fe}(\mathrm{CN})_{6}]^{4-} \), which has a charge of 4-(d) \(\mathrm{Cl}^{-} \), which has a charge of 1-.

Step 3: Applying the Schulze-Hardy Rule

According to the Schulze-Hardy rule, the coagulating power of an ion is proportional to the sixth power of its charge. This means ions with higher charges will have lower flocculation values since they are more effective in causing coagulation.

Step 4: Comparing Ions Based on Charges

Since coagulating power increases with ion charge, \([\mathrm{Fe}(\mathrm{CN})_{6}]^{4-} \) with charge 4- will have the strongest coagulating power and thus the lowest flocculation value. Conversely, \(\mathrm{Cl}^{-}\) with charge 1- has the weakest coagulating power and thus the highest flocculation value among the given ions.

Step 5: Conclusion

Based on charge and the Schulze-Hardy rule, \([\mathrm{Fe}(\mathrm{CN})_{6}]^{4-}\) has the least flocculation value as it has the highest charge, making it highly effective in causing coagulation.

Key Concepts

Schulze-Hardy Rule

The Schulze-Hardy Rule is a cornerstone principle in colloidal chemistry. It states that the coagulating power of an ion is related to the sixth power of its charge. This rule is crucial in understanding how ions interact with colloidal particles. When an ion possesses a higher charge, it can destabilize and coagulate colloidal particles more efficiently.

The concept can be simplified by considering the effectiveness of different ions based on their charges. A highly charged ion exerts a strong attraction on the charged surface of a colloidal particle, facilitating its neutralization and eventual settling out of solution. This intrinsic aspect of ion interaction is what makes the Schulze-Hardy Rule so vital in predicting flocculation values.

In practical applications, this rule is applied to determine how much of a particular ion is needed to induce coagulation in colloidal systems. The less concentration required, the higher the coagulating power due to the effect of the charge. This understanding helps in experiments and formulations within chemical industries that aim to control or modify the behavior of colloidal particles.

Ion Charge and Coagulating Power

Ion charge is not just a number, it significantly affects its ability to coagulate colloidal particles. The basic idea is simple: higher charges lead to stronger attraction forces, which means better coagulating power.

When it comes to causing particles to clump together and settle out of a solution, ions with higher charges are far more efficient. They generate stronger electrical fields around them, pulling colloidal particles closer and overcoming the repulsion between the particles. This results in a more compact and stable aggregation.

• Higher charge equals stronger attraction.
• Better attraction leads to more effective coagulation.
• An ion's charge directly influences how it interacts with charged colloidal particles.

Understanding the relationship between ion charges and their coagulating power helps in selecting appropriate ions to manipulate colloidal systems. This is essential in applications ranging from water purification to chemical manufacturing.

Colloidal Particle Coagulation

Colloidal particles are typically stabilized in a solution by surface charges that prevent them from clumping together. However, for various industrial and research processes, coagulating these particles can be desirable.

Coagulation is the process where dispersed colloidal particles come together to form larger aggregates, often eventually leading to settleable forms. The method of coagulation depends significantly on the nature of the stabilizing charge of the colloidal particles and the ions introduced into the system.

The process involves neutralizing the particle charges so that they can collide and stick together. Here's how the process usually occurs:

• Introduce ions with the opposite charge to the colloidal particles.
• The ions will interact with the particle surfaces, neutralizing their charges.
• This reduces repulsion between particles, allowing them to aggregate.

Colloidal coagulation is employed in various fields such as wastewater treatment, where it aids in the removal of suspended particles from water. By selecting appropriate ions based on their charge and concentration, efficient coagulation and separation of colloidal particles can be achieved, making this an essential process in the management and treatment of colloidal systems.