Question

Which of the following will have the highest coagulating power for \(\mathrm{Fe}(\mathrm{OH})_{3}\) conon (a) \(\mathrm{PO}_{4}^{3-}\) (b) \(\mathrm{SO}_{4}^{2-}\) (c) \(\mathrm{Ca}^{2+}\) (d) \(\mathrm{Al}^{3+}\)

Short answer

\(\mathrm{Al}^{3+}\) has the highest coagulating power for \(\mathrm{Fe}(\mathrm{OH})_{3}\) colloidal solution.

Step-by-step solution

Understand the Hardy-Schulze Rule

The Hardy-Schulze rule states that the coagulating power of an ion increases with its valency. This means that the higher the charge on an ion, the more efficient it is at causing coagulation. The rule applies to both anions and cations.

Identify the Charges on the Given Ions

Examine the given ions and note their charges: (a) \(\mathrm{PO}_{4}^{3-}\) is a trivalent anion with a charge of -3.(b) \(\mathrm{SO}_{4}^{2-}\) is a divalent anion with a charge of -2.(c) \(\mathrm{Ca}^{2+}\) is a divalent cation with a charge of +2.(d) \(\mathrm{Al}^{3+}\) is a trivalent cation with a charge of +3.

Determine the Ion with the Highest Coagulating Power

According to the Hardy-Schulze rule, the ion with the highest valency will have the highest coagulating power. Comparing the charges of the given ions, \(\mathrm{Al}^{3+}\) has the highest charge and thus, the highest coagulating power.

Key concepts

Coagulating Power

Coagulating power refers to the ability of an ion in a solution to cause the precipitation or aggregation of colloidal particles. This concept is important in understanding how pollutants are removed from water, as well as in various processes in the chemical industry.

Colloidal particles are small particles that typically remain suspended in a solution. These particles bear a charge, which prevents them from coming together due to repulsion. The addition of ions with a charge opposite to the particles can neutralize this charge and lead to coagulation or clustering of the colloidal particles.

• The greater the charge on an ion, the greater its coagulating power.
• Coagulating agents are often used in water treatment to remove impurities.

In the exercise, ions were examined for their ability to coagulate \(\mathrm{Fe}(\mathrm{OH})_{3}\) colloids. The solution concluded that based on their charge, \(\mathrm{Al}^{3+}\) ions would have the greatest coagulating power, which is in alignment with the principles of the Hardy-Schulze rule.

Valency and Coagulation

Valency plays a pivotal role in determining the coagulating power of ions according to the Hardy-Schulze rule. The rule establishes a direct relationship between the valency of an ion and its ability to coagulate colloidal particles.

Valency refers to the combining power of an element or ion, which is determined by the number of electrons that an atom can lose, gain, or share. It is reflected in an ion's charge and is critical for understanding its interactions within a solution.

• Higher valency means a higher charge, and hence, a greater ability to neutralize the charges on colloidal particles.
• This concept is used to predict the efficiency of various coagulating agents.

In the context of the exercise, recognizing the relationship between valency and the efficiency of coagulation was key to identifying \(\mathrm{Al}^{3+}\) as the ion with the highest coagulating power. It's critical to consider both valency and the nature of the ions (whether they are cations or anions) when predicting coagulation effectiveness.

Ion Charges

Ion charges are fundamental to understanding a wide range of chemical processes, including coagulation. Ions are atoms or molecules that have gained or lost electrons, resulting in a net positive or negative charge. The magnitude of the charge correlates with an ion's ability to interact with surrounding substances.

In a solution, these charges can influence various properties and behaviors, including:

• The solubility of compounds
• The electrical conductivity of the solution
• The rate of reaction between ions

When discussing coagulation, it is the interaction between ion charges and the surface charge of colloidal particles that is fundamental to the process. By understanding the charges of the ions involved, as shown in the exercise with \(\mathrm{PO}_{4}^{3-}\), \(\mathrm{SO}_{4}^{2-}\), \(\mathrm{Ca}^{2+}\), and \(\mathrm{Al}^{3+}\), we can predict and control the coagulation of colloids. The Hardy-Schulze rule helps us make sense of these interactions, explaining why \(\mathrm{Al}^{3+}\) with its highest charge (+3) has the highest coagulating power among the given options.