Question

When zeolite, which is hydrated sodium aluminium silicate, is treated with hard water the sodium ions are exchanged with: 1\. \(\mathrm{H}^{+}\) ions 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

Short answer

(a) 2,4

Step-by-step solution

Understanding Zeolite Role

Zeolite functions mainly as an ion exchanger. When hard water, which contains high concentrations of calcium (\(\mathrm{Ca}^{2+}\)) and magnesium (\(\mathrm{Mg}^{2+}\)) ions, passes through zeolite, these ions are exchanged for sodium (\(\mathrm{Na}^{+}\)) ions present in the zeolite.

Identifying Exchangeable Ions

The sodium ions in zeolite are exchanged mainly with the calcium (\(\mathrm{Ca}^{2+}\)) and magnesium (\(\mathrm{Mg}^{2+}\)) ions in the hard water. These ions are responsible for water hardness.

Eliminate Incorrect Options

The question options include hydrogen ions (\(\mathrm{H}^{+}\)), sulfate ions (\(\mathrm{SO}_{4}^{-2}\)), and a nonexistent fifth option not provided. Zeolite does not typically exchange sodium with \(\mathrm{H}^{+}\) or \(\mathrm{SO}_{4}^{-2}\) ions, nor with any unspecified option '5'.

Choose the Correct Answer

The sodium ions are exchanged for \(\mathrm{Ca}^{2+}\) and \(\mathrm{Mg}^{2+}\) ions. Therefore, the correct answer based on this exchange process is option (a) 2,4.

Key concepts

Ion Exchange

Ion exchange is a process where ions in a solution are swapped with ions on a solid medium. In the case of water softening with zeolite, the zeolite acts as the solid medium. This solid is rich in sodium ions, which it readily exchanges with calcium and magnesium ions from hard water. This exchange process is essential because it removes the calcium and magnesium ions, which are responsible for making water "hard."
- Zeolite is particularly effective for this task because of its highly porous structure. This structure maximizes the surface area for ion exchange, making it incredibly efficient.
- As calcium and magnesium ions bind strongly to the zeolite, they displace sodium ions. This exchange significantly reduces the hardness of the water.

Hard Water

Hard water is water that contains high levels of dissolved minerals, primarily calcium ( Ca^{2+} ) and magnesium ( Mg^{2+} ) ions. These ions become dissolved in the water as it flows over or through rocks and soil that are rich in these minerals. Hard water is a common occurrence in many regions and can lead to several problems.
- Hard water can cause scale buildup in pipes and appliances, reducing their efficiency and lifespan.
- It can also lead to soap scum, which is a sticky residue that makes cleaning tasks more challenging. This happens because the minerals in hard water react with soap, preventing it from lathering properly.
To combat these issues, water softening methods, like using zeolite, are employed to remove the hardness-causing ions from the water.

Calcium Ions

Calcium ions ( Ca^{2+} ) are one of the primary contributors to hard water. They originate from the dissolution of calcium-rich minerals such as limestone and gypsum. When these minerals dissolve in water, calcium ions are released, increasing water hardness.
- While calcium ions are beneficial to health, providing an important mineral needed for strong bones and teeth, they can cause problems in water systems.
- In domestic settings, the presence of calcium ions leads to scale formation. As water is heated, calcium precipitates out, forming solid deposits that can clog pipes and reduce the efficiency of water heaters.
Using zeolite for ion exchange is an effective way to remove calcium ions from water, thus softening it. By replacing calcium ions with sodium ions, zeolite helps to reduce the negative effects associated with hard water.

Magnesium Ions

Magnesium ions ( Mg^{2+} ) are another key component of hard water alongside calcium ions. These ions enter the water supply from the dissolution of magnesium-rich minerals such as dolomite and magnesite.
- Magnesium in small amounts is essential for human health, playing a role in muscle and nerve function, as well as maintaining strong bones.
- However, like calcium, excessive magnesium in water can lead to similar problems such as scale buildup and reduced effectiveness of soaps and detergents.
The presence of these ions can make water taste different and can contribute to cloudy water due to precipitation when boiled or evaporated. Zeolite's ion exchange capability is important for removing magnesium ions from water, thereby preventing the inconveniences and potential damage associated with hard water.