Question

Which colloids can be coagulated by \(\mathrm{Al}^{+3}\) here? (a) \(\mathrm{Al}_{2} \mathrm{~S}_{3}\) (b) \(\mathrm{CdS}\) (c) \(\mathrm{T}_{1} \mathrm{O}_{2}\) (d) Hae moglobin

Short answer

CdS and negatively charged Hemoglobin can be coagulated by \(\mathrm{Al}^{+3}\).

Step-by-step solution

Understanding Coagulation

Before solving the exercise, it's important to understand that coagulation of colloids occurs when an oppositely charged ion is introduced, neutralizing the charge on the colloidal particles. This neutralization leads to the particles aggregating and settling out of solution.

Identifying Charges on Colloids

Analyze the charge on the colloidal particles: 1. (a) Aluminium sulfide Sulphide ions ext{( ext{S}^{2−})} would be negatively charged. 2. (b) Cadmium Sulfide (CdS) is a slightly negatively charged colloid. 3. (c) Generally, Titanium dioxide (TiO2) can carry either positive or negative charge depending on the medium, but typically it's neutral. 4. (d) Hemoglobin is a protein that can be negatively charged depending on the pH of the medium.

Charge Neutralization By \\(\mathrm{Al}^{+3}\\)

Aluminium ions \(\mathrm{Al}^{+3}\) are positively charged and can neutralize negatively charged particles in the solution. Therefore, colloids with a negative charge would be coagulated upon interaction with \(\mathrm{Al}^{+3}\)..

Identifying Suitable Colloids

Given the ability of \(\mathrm{Al}^{+3}\) to coagulate negatively charged colloids, 1. (b) CdS would be coagulated due to its slightly negative charge.2. (d) Hemoglobin can be coagulated if it's negatively charged in the solution medium.

Key concepts

Aluminium ions

Aluminium ions, denoted as \(\mathrm{Al}^{+3}\), play a significant role in the process of coagulation of colloids. These ions are characterized by their strong positive charge due to the loss of three electrons. This high charge density makes \(\mathrm{Al}^{+3}\) highly effective at interacting with negatively charged particles in a colloidal system.
The ions are sourced from compounds like aluminum sulfate or aluminum chloride, which are commonly used in water treatment processes. When introduced to a solution, \(\mathrm{Al}^{+3}\) helps to bridge the gap between negatively charged colloidal particles by counteracting their charge, which results in neutralization and ultimately leads to coagulation.

Negative charge

Negative charges on colloidal particles arise due to an uneven distribution of particles at the colloidal interface. This can often occur because of ion adsorption, lattice imperfections, or surface ionization.
In the context of the respective colloids:

• For substances like Cadmium Sulfide (\(\mathrm{CdS}\)), there is a general tendency to acquire a negative charge.
• Proteins such as Hemoglobin can vary in charge depending on environmental conditions like pH, often being negatively charged in basic or neutral solutions.

Understanding how these charges interact with ions like \(\mathrm{Al}^{+3}\) is central to comprehending the coagulation process.

Charge neutralization

Charge neutralization is a core mechanism in the coagulation process. It involves the reduction or elimination of the electrical charge present on the surface of colloidal particles.
When \(\mathrm{Al}^{+3}\) ions are introduced into a solution containing negatively charged colloids, they are attracted to these particles due to the principle of opposite charges attracting.

• This interaction reduces the electrostatic repulsion between particles, bringing them closer together.
• As a result, the individual colloidal particles lose their repulsive forces and start to aggregate.

This aggregation is a key step that facilitates the removal of colloids from solution as they form larger, settleable aggregates.

Coagulation mechanism

The coagulation mechanism is the overall process that leads to the stabilization and eventual separation of colloids from a solution. This mechanism can be broken down into key steps:

• Initial Interaction: Charged ions, like \(\mathrm{Al}^{+3}\), are introduced to the solution where they interact with oppositely charged colloids.
• Neutralization: The positive ions neutralize the negative surface charge on colloidal particles, drastically reducing repulsive forces.
• Aggregation: Once neutralized, particles begin to aggregate, forming larger clumps or flocs.
• Settlement: These larger aggregates increase in density and begin to settle out of the solution due to gravity.

Understanding these steps helps to explain how \(\mathrm{Al}^{+3}\) can effectively coagulate colloids like \(\mathrm{CdS}\) and certain forms of Hemoglobin in the correct medium.