Question

By which of the following process permanent hardness of water can be removed? (a) Washing soda (b) Soda lime (c) Sodium chloride (d) Sodium bicarbonate

Short answer

The permanent hardness of water can be removed by using washing soda (option a).

Step-by-step solution

Understand Permanent Hardness

Permanent hardness of water is caused by the presence of calcium and magnesium salts, specifically chlorides and sulfates, in the water. Unlike temporary hardness, it does not get removed by boiling the water. We need a specific process to remove these minerals to soften the water.

Review the Options

Consider each of the given options: (a) Washing soda, (b) Soda lime, (c) Sodium chloride, and (d) Sodium bicarbonate, and think about their properties and effectiveness in removing hardness.

Identify the Correct Chemical

Washing soda, or sodium carbonate ( ext{Na}_2 ext{CO}_3), is known for its ability to precipitate calcium and magnesium ions in water as insoluble carbonates. This process removes the permanent hardness of water effectively. None of the other substances listed can perform this task effectively. For example, soda lime is used for other chemical purposes, sodium chloride is common salt, and sodium bicarbonate is not effective in removing permanent hardness.

Conclusion

Given the effectiveness of washing soda in precipitating calcium and magnesium ions, the correct choice is washing soda for removing the permanent hardness of water.

Key concepts

Permanent Hardness

Permanent hardness in water is a common issue that cannot be resolved by simply boiling it. This type of hardness is mainly due to the presence of calcium and magnesium salts, specifically as chlorides and sulfates.
Unlike temporary hardness, which can be removed by heating the water, permanent hardness requires a chemical process to be dealt with effectively.
It's important to understand that these minerals remain dissolved in the water under normal conditions, making them much more challenging to eliminate.

Calcium Salts

Calcium salts, such as calcium chloride and calcium sulfate, contribute significantly to the permanent hardness of water. These compounds are formed when calcium, a natural element found in the earth’s crust, combines with different anions.
They are highly soluble in water, which is why they persist and become a challenge in hard water.

• Calcium chloride (CaCl₂) is often encountered in seawater or as a de-icing agent.
• Calcium sulfate (CaSO₄), also known as gypsum, is found in various minerals.

The presence of these salts in water means that simple heating won't be able to remove them, necessitating further treatment methods like using washing soda.

Magnesium Salts

Similar to calcium salts, magnesium salts also contribute to the permanency of hard water. These salts, like magnesium chloride and magnesium sulfate, maintain their solubility in water, making them difficult to remove through simple methods.

• Magnesium chloride (MgCl₂) is commonly present in seawater.
• Magnesium sulfate (MgSO₄), familiarly known as Epsom salt, is frequently used in bath salts.

High levels of magnesium in drinking water can affect the water's taste and lead to scale buildup in pipes and appliances.
To combat this, specific treatments like the addition of washing soda or the use of water softeners are implemented to precipitate these salts out of the water.

Water Softening

Water softening is the process used to remove permanent hardness in water caused by calcium and magnesium salts.
One common approach to softening hard water is through the use of washing soda, or sodium carbonate ( ext{Na}_2 ext{CO}_3). This chemical reacts with calcium and magnesium ions to form insoluble carbonates, which can then be filtered out of the water.
Other methods include:

• Using ion-exchange resins which replace calcium and magnesium ions with sodium or potassium ions.


• Implementing reverse osmosis systems that filter out these ions effectively.

Ultimately, softening water helps extend the lifespan of plumbing systems and improves the effectiveness of soaps and detergents.