Question

Alum is widely used to purify water since \(\quad\) (a) it forms complex with clay particles (b) it coagulates the mud particles (c) it exchanges \(\mathrm{Ca}^{2+}\) and \(\mathrm{Mg}^{2+}\) ions present in hard water (d) its sulphate ion is water purifier

Short answer

The correct answer is (b) alum coagulates the mud particles.

Step-by-step solution

Understanding Water Purification with Alum

Alum is commonly used in water purification processes because of its ability to cause suspended particles to clump together, making them easier to remove. This process is known as coagulation.

Analyzing the Given Options

We need to evaluate each provided option to determine which correctly describes alum's role in water purification. The options describe its actions such as forming complexes, coagulating particles, ion exchange, and the role of sulphate ions.

Evaluating Option (b)

Option (b) states that alum coagulates the mud particles. This is the primary function of alum in water purification as it causes the small particles to stick together, forming larger particles that can settle out of the water.

Reviewing Other Options

Option (a) discusses forming a complex with clay particles, which is not correct. Option (c) refers to ion exchange applicable to water softening, not purification with alum. Option (d) incorrectly attributes purifying properties to sulphate ions, which are not involved in water purification.

Conclusion

From the evaluation, option (b) is the correct mechanism of action for alum in water purification: it coagulates mud particles, allowing them to be removed easily.

Key concepts

Alum

Alum is a chemical compound commonly used in water purification. It is an aluminum-based compound, typically existing in the form of a white, crystalline powder. When added to water, alum plays a crucial role in enhancing the clarity and safety of the water.

The primary function of alum in the purification process is due to its coagulating properties. It helps to clump together dirt and particles suspended in water, allowing them to settle at the bottom. This collective settling is known as sedimentation. The process effectively reduces turbidity, leaving the water clearer and easier to filter.

Alum is prized in water treatment for its efficiency and cost-effectiveness. It has been trusted for centuries and remains a go-to solution for municipal and industrial water systems worldwide.

Coagulation

Coagulation is an essential process in the water purification system. It involves using a coagulant like alum to compact suspended particles, causing them to aggregate into larger pieces called flocs. These flocs are easier to remove via sedimentation or filtration methods.

During coagulation, the alum neutralizes the negative charges that keep particles apart in water. As these charges are neutralized, they can no longer repel each other, and thus, they begin to clump together. This process is particularly important for removing materials such as:

• Mud particles
• Organic matter
• Bacteria and microorganisms
• Fine particulates

The efficiency of coagulation not only improves the physical quality of the water but also contributes to the removal of pathogens, enhancing the overall safety of the water supply.

Mud Particles

Mud particles found in water are typically small and tend to remain suspended due to their lightweight nature. If not properly removed, they can cause the water to appear cloudy and unappealing. Additionally, suspended mud particles can harbor harmful bacteria and pollutants that could impact human health if consumed.

The coagulation process facilitated by alum is essential for addressing the issue of mud particles in the water. By causing these particles to coalesce, they become heavier and eventually settle down. This sedimentation process allows the clearer water to rise to the surface, where it can be further purified and filtered for consumption.

Removing mud particles effectively improves the aesthetic quality of the water and reduces the potential health risks associated with drinking or using contaminated water.

Suspended Particles

Suspended particles are tiny bits of material floating in the water that can range from algae, plankton, or silt to organic and inorganic debris. These particles do not dissolve in water and may contribute to poor water quality.

Truly purifying water necessitates the removal of these particles. Alum is instrumental in removing suspended particles due to its coagulating action. By clumping them together, it facilitates their removal through methods like filtration and sedimentation.

The presence of suspended particles in water can hinder not only the visual clarity but also the safety of water if left unaddressed. Effective removal can enhance both the physical and chemical qualities of the water, ensuring its safety and suitability for various uses.