Problem 55 - A Complete Resource Book in Chemistry for JEE Main

Question

Alum purifies muddy water by (a) absorption (b) dialysis (c) emulsifying properties (d) coagulation

Step-by-Step Solution

Answer

Alum purifies muddy water by (d) coagulation.

Step 1: Understanding Coagulation

Coagulation is a process where particles in the water clump together to form larger particles, often called flocs, which can settle out of the water. This is commonly used in water treatment to remove suspended particles, making the water clearer.

Step 2: Role of Alum in Water Treatment

Alum, also known as aluminum sulfate, is added to muddy water as a coagulant. It helps in the formation of flocs by neutralizing the charge of the suspended particles in the water, allowing them to clump together.

Step 3: Comparing the Options

Let's examine the options to see which one aligns with the function of alum. - (a) Absorption: This involves a substance taking in or soaking up another substance, which does not match the role of alum. - (b) Dialysis: This process involves separating particles based on their ability to pass through a membrane, unrelated to alum's role. - (c) Emulsifying Properties: Refers to mixing two immiscible liquids, which doesn't pertain to alum's action. - (d) Coagulation: Matches the function of alum in water treatment by causing particles to clump together.

Step 4: Selecting the Correct Answer

Based on the above analysis, option (d) coagulation matches the role of alum in purifying muddy water by helping particles to combine and settle, leading to clearer water.

Key Concepts

Role of Alum

In the fascinating world of water treatment, alum, short for aluminum sulfate, plays a critical role. It's a coagulant, which means it's a substance that helps particles stick together. When added to water, alum neutralizes the charges on suspended particles. These could be bits of dirt or microorganisms that keep the water cloudy.

Once these particles lose their charge, they begin to clump together. This process effectively creates larger and more easily removable clusters called flocs. The power of alum in water treatment lies in its ability to convert difficult-to-remove tiny particles into larger ones, making water much cleaner and safer for consumption.

• Neutralizes charge on particles
• Facilitates floc formation
• Enhances particle removal

As a result, alum is a cornerstone in many water purification systems, ensuring that the water we use daily is both clear and free of harmful particles.

Water Purification Processes

Water purification comprises several essential processes that work together to provide safe and clean water. Understanding these processes can help us appreciate how raw water transforms into the drinkable water that flows from our taps.

One key process is coagulation and flocculation, where substances like alum are used to gather small particles into larger clumps. Following this, sedimentation allows these larger particles to settle at the bottom of the treatment tank, making them easier to remove.

Another critical step is filtration, where the water passes through layers of sand, gravel, and charcoal to remove any remaining particulates. Finally, disinfection occurs, typically involving chlorine or ultraviolet light, to kill remaining pathogens.

• Coagulation and flocculation
• Sedimentation
• Filtration
• Disinfection

Each step is vital, ensuring water safety and quality before it reaches our homes.

Particle Settling in Water Treatment

The settling of particles is a pivotal stage in water treatment, ensuring impurities are effectively removed. This process primarily occurs after coagulation and flocculation, where small particles are gathered into larger flocs.

During settling, also known as sedimentation, these dense flocs slowly sink to the bottom of the water basin. The settling behavior depends on factors like the size and weight of the flocs, the temperature of the water, and the basin design.

This gravitational separation technique effectively clears water of suspended impurities and plays a huge role in overall water clarity.

• Occurs after coagulation
• Ensures gravitational separation
• Improves water clarity

Through effective particle settling, water treatment facilities can elevate water quality, creating a safer resource for communities.