Question

Water softening by Clarke's process uses: (a) Potash alum (b) Calcium bicarbonate (c) Calcium hydroxide (d) Sodium bicarbonate

Short answer

The correct answer is (c) Calcium hydroxide.

Step-by-step solution

Understanding Clarke's Process

Clarke's process is used for the softening of hard water. It involves adding a chemical to water to remove hardness caused mainly by calcium and magnesium ions.

Identifying the Chemical Used

In Clarke's process, calcium hydroxide, also known as lime, is the chemical used to treat hard water. When calcium hydroxide is added to water containing calcium bicarbonate, it reacts to form insoluble calcium carbonate, which precipitates out of the solution, thereby softening the water.

Analyzing Options

Looking at the given options: (a) Potash alum, (b) Calcium bicarbonate, (c) Calcium hydroxide, (d) Sodium bicarbonate. We identify that option (c) Calcium hydroxide corresponds to the chemical used in Clarke's process for water softening.

Key concepts

Water Softening

Water softening is the process of removing minerals that cause water to be hard. Hard water contains high concentrations of calcium and magnesium ions, which can lead to several problems. For example, these ions can form scale that clogs pipes and ruins appliances. This is why softening water becomes crucial, especially for households and industries that rely on clean and efficient water systems.

Softened water has numerous benefits:

• Improves the effectiveness of soaps and detergents by producing more lather.
• Prevents limescale buildup in pipes and appliances, extending their lifespan.
• Improves the taste and appearance of water for drinking and cooking purposes.

There are various methods to soften water, and Clarke's process is one effective chemical method among them.

Calcium Hydroxide

Calcium hydroxide, often referred to as lime, is a key component in many industries, including water treatment. In the context of water softening, it plays a significant role, especially in Clarke's process.

Calcium hydroxide is represented by the chemical formula \( Ca(OH)_2 \) and is a white powdery substance. When added to water containing calcium bicarbonate \((Ca(HCO_3)_2)\), a reaction occurs. This reaction forms calcium carbonate \((CaCO_3)\), which is insoluble in water: \[ Ca(OH)_2 + Ca(HCO_3)_2 \rightarrow 2 CaCO_3 + 2 H_2O \]The calcium carbonate precipitates out of the water, effectively removing the hardness and making the water soft. This simplicity and efficiency make calcium hydroxide an appealing choice for water softening in various applications.

Hard Water Removal

The removal of hard water agents is essential for maintaining healthy pipelines and household appliances. Hard water, characterized by a high mineral content, can cause several issues due to the presence of calcium and magnesium ions.

There are different strategies for hard water removal:

• Chemical methods: These include the use of substances like calcium hydroxide which react with water impurities to form insoluble compounds that can be easily removed.
• Ion-exchange systems: These systems swap calcium and magnesium ions with sodium ions to soften the water.
• Reverse osmosis: A physical method where water is forced through membranes to remove impurities including ions contributing to hardness.

Each method has its own advantages. Clarke's process, using calcium hydroxide, is particularly effective because it's straightforward and yields immediate results. Understanding these methods allows you to choose the best approach for your specific needs in combating hard water issues.