Problem 132 - A Complete Resource Book in Chemistry for JEE Main

Question

When zeolite, which is hydrated sodium aluminium silicate, is treated with hard water the sodium ions are exchanged with 1\. H tons 2\. \(\mathrm{Ca}^{2+}\) ions 3\. \(\mathrm{SO}_{4}^{-2}\) ions 4\. \(\mathrm{Mg}^{2+}\) ions (a) 2,4 (b) \(1,2,3\) (c) \(2,4,5\) (d) all are correct

Step-by-Step Solution

Answer

Option (a) 2,4 is correct.

Step 1: Understanding Zeolite and Hard Water

Zeolite is a hydrated sodium aluminium silicate. Hard water contains calcium and magnesium ions, primarily responsible for water hardness.

Step 2: Role of Zeolite in Ion Exchange

Zeolite acts as an ion exchange resin that exchanges sodium ions with certain ions present in hard water. This process removes the hardness from water.

Step 3: Identifying Ions in Hard Water

Hard water mostly contains calcium ions \( (\mathrm{Ca}^{2+}) \) and magnesium ions \( (\mathrm{Mg}^{2+}) \). These ions are known for causing hardness in water.

Step 4: Determining the Ions Exchanged

In an ion exchange process, sodium ions in zeolite exchange places with calcium \((\mathrm{Ca}^{2+})\) and magnesium ions \((\mathrm{Mg}^{2+})\) in hard water, softening it.

Step 5: Choosing the Correct Option

Based on the information above, zeolite exchanges sodium ions with \( \mathrm{Ca}^{2+} \) and \( \mathrm{Mg}^{2+} \) ions. The correct answer is 2 and 4, which is option (a).

Key Concepts

Understanding Hard Water

Hard water is water that contains high levels of dissolved minerals, particularly calcium and magnesium ions.
These minerals are picked up by water as it travels through the ground, especially in areas rich in limestone or gypsum.

• Calcium ions \( (\mathrm{Ca}^{2+}) \) are commonly present in water that has seeped through rocks like calcium carbonate or calcium sulfate.
• Magnesium ions \( (\mathrm{Mg}^{2+}) \) often come from minerals such as dolomite and magnesium carbonate.

These minerals are what primarily contribute to the water's hardness, leading to several practical issues such as scaling in pipes, reduced efficiency of soaps and detergents, and spots on dishes and glassware.

The Role of Calcium Ions in Hard Water

Calcium ions are one of the main culprits when it comes to water hardness.
They come from leaching calcium dissolved from mineral deposits such as limestone and chalk.

• When calcium ions are present in large quantities, they react with soap to form soap scum instead of lather, thereby reducing the soap's cleaning capacity.
• They also tend to precipitate out in the form of calcium carbonate when heated, leading to the buildup of limescale in boilers, kettles, and on plumbing fixtures.

Since these ions are positively charged, they are ideal candidates for exchange by negatively charged ions in an ion exchange process, such as those in a zeolite system.

The Influence of Magnesium Ions on Hard Water

Much like calcium, magnesium ions also contribute significantly to the hardness of water.
Magnesium is often found in groundwater sources as it is the eighth-most abundant element.

• High levels of magnesium in water can lead to scaling, similar to the effects caused by calcium ions.
• In addition to scaling, magnesium in hard water can increase the corrosiveness of the water, potentially harming appliances and plumbing systems.

The presence of these ions is another factor that necessitates water softening techniques, such as using a zeolite system for ion exchange, to improve water quality and usability.

Explaining Water Softening

Water softening is a crucial process that tackles the issues caused by hard water.
One effective method is through the use of ion exchange resins, such as zeolite.

• Zeolite, a sodium aluminium silicate, exchanges its sodium ions with calcium and magnesium ions, successfully removing them from the water.
• As the calcium and magnesium ions bind to the zeolite, the sodium ions are released, effectively softening the water by lowering its hardness.
• This exchange process is vital for preventing scale buildup and enhancing soap efficiency, making water more suitable for household and industrial applications.

By understanding and utilizing zeolite ion exchange, we can convert hard water into soft water, thereby mitigating many associated problems.