Question

Water is often treated with chlorine to: (a) Kill germs (b) Remove hardness (c) Increase oxygen content (d) Remove suspended particles

Short answer

Chlorine is added to water mainly to kill germs (option a).

Step-by-step solution

Understand the Purpose of Chlorine

Chlorine is commonly used in water treatment processes. Understanding what properties chlorine contributes to water can help identify the correct answer to this question.

Assess Option (a) Kill Germs

Chlorine is a powerful disinfectant and is primarily used for killing germs (bacteria, viruses, and other microorganisms) in water, making it safe for drinking.

Assess Option (b) Remove Hardness

Water hardness is generally caused by the presence of calcium and magnesium ions. Chlorine does not remove hardness; other treatments like ion exchange are used for this purpose.

Assess Option (c) Increase Oxygen Content

Chlorine does not increase the oxygen content of water. Oxygenation is generally done through aeration processes.

Assess Option (d) Remove Suspended Particles

Chlorine does not remove suspended particles. Filtration or coagulation processes are used to remove suspended particles.

Identify the Correct Option

The primary reason chlorine is added to water is to disinfect it by killing germs, so option (a) is correct.

Key concepts

Chlorine Disinfection

Chlorine disinfection plays a crucial role in making water safe to drink. This process involves adding chlorine or chlorine compounds to water to eliminate harmful microorganisms. These microorganisms can pose severe health risks if consumed. By disinfecting water, chlorine effectively reduces the spread of diseases like cholera, dysentery, and typhoid fever.
Additionally, the widespread use of chlorine in water treatment is due to its availability and cost-effectiveness. It can reach every corner of the water distribution systems, ensuring consistent protection against pathogens.

• Chlorine is often introduced as a gas or in liquid form (sodium hypochlorite).
• Once dissolved in water, it forms hypochlorous acid, a potent germ-killer.
• The process is swift, making it efficient for large-scale water treatment plants.

Overall, chlorine disinfection remains a cornerstone of public health measures worldwide, significantly reducing the risk of waterborne illnesses.

Germicidal Properties of Chlorine

The germicidal properties of chlorine make it an exceptional tool in the fight against dangerous microorganisms. When chlorine is added to water, it reacts to form hypochlorous acid, which aggressively targets and destroys cell walls of bacteria and viruses. This effectively neutralizes harmful pathogens, rendering them unable to reproduce or cause illness.
The effectiveness of chlorine can be attributed to its ability to penetrate the protective layers of microorganisms. Once inside, it disrupts vital cellular processes, leading to cell death.

• Chlorine’s broad-spectrum germicidal ability means it can handle a wide array of pathogens.
• It is particularly effective against bacteria, viruses, and some protozoans.
• The concentration and contact time are crucial for the complete inactivation of microorganisms.

However, while chlorine is potent, it is essential to monitor levels to avoid any adverse effects on health and taste. Chlorine's germicidal properties are invaluable in maintaining public health through safe drinking water.

Water Hardness Removal Methods

Water hardness is a common issue caused by the presence of calcium and magnesium ions in water. These minerals can lead to scaling in pipes and appliances, affecting water quality and efficiency. Chlorine does not remove hardness; instead, other methods are employed for this purpose.
One popular technique for removing hardness is ion exchange, which swaps calcium and magnesium ions for sodium ions. This process involves using a resin bed where hard ions attach to the resin and are replaced with sodium ions.

• Softening systems that use ion exchange are effective for both residential and industrial applications.
• Lime softening is another method, which involves adding lime (calcium hydroxide) to precipitate out calcium and magnesium as insoluble solids.
• Reverse osmosis can also reduce hardness by filtering out minerals through a semi-permeable membrane.

Each method has its benefits and limitations, so the choice of system primarily depends on the context and specific requirements of water use.