Problem 20 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

When zeolite, which is hydrated sodium aluminium silicate, is treated with hard water the sodium ions are exchanged with [1990-1 Mark] (a) \(\mathrm{H}^{+}\)ions (b) \(\mathrm{Ca}^{++}\)ions (c) \(\mathrm{SO}_{4}^{-}\)ions (d) \(\mathrm{Mg}^{++}\)ions (e) \(\mathrm{OH}^{-}\)ions

Step-by-Step Solution

Answer

Sodium ions in zeolite are exchanged with \(\mathrm{Ca}^{++}\) ions.

Step 1: Understanding Zeolite

Zeolite is a type of chemical compound used in water softening. It exchanges its sodium ions with other ions present in hard water.

Step 2: Identify the Ions in Hard Water

Hard water mainly contains calcium (\(\mathrm{Ca}^{++}\)) and magnesium ions (\(\mathrm{Mg}^{++}\)). These are the ions responsible for water hardness.

Step 3: Determine the Zeolite Exchange Ion

When zeolite is used to treat hard water, it exchanges its sodium ions with the ions causing hardness, which are primarily \(\mathrm{Ca}^{++}\) and \(\mathrm{Mg}^{++}\) ions.

Step 4: Find the Correct Option

The options provided are \(\mathrm{H}^{+}\), \(\mathrm{Ca}^{++}\), \(\mathrm{SO}_{4}^{-}\), \(\mathrm{Mg}^{++}\), and \(\mathrm{OH}^{-}\). The common exchange occurs with \(\mathrm{Ca}^{++}\) and \(\mathrm{Mg}^{++}\) ions. Therefore, the answer could be either \(\mathrm{Ca}^{++}\) or \(\mathrm{Mg}^{++}\).

Key Concepts

Water Softening

Water softening is a crucial process that helps to reduce the hardness of water. This hardness is typically due to the presence of minerals like calcium and magnesium. Hard water can cause numerous issues, from reducing the effectiveness of soaps and detergents to forming scale in pipes and appliances.
By softening the water, you allow it to work better with soaps, reduce scale formation, and extend the lifespan of plumbing systems. There are various methods to soften water, but one of the most popular is ion exchange using zeolites.
This process removes the "hard" ions and makes the water "soft," meaning it's more compatible with soap and less likely to cause scale.

Ion Exchange

Ion exchange is a process where unwanted dissolved ions in a liquid are replaced with other ions. In water treatment, ion exchange typically replaces calcium and magnesium ions, which contribute to water hardness, with sodium ions from substances like zeolite.
When water passes through a bed of zeolite, the sodium ions are swapped with the calcium and magnesium ions present in the water. This exchange helps convert hard water into soft water.
Key benefits of ion exchange include its efficiency in removing hardness and its ability to operate continuously, as zeolites can be regenerated once they are saturated with calcium and magnesium ions.

Hard Water

Hard water is a common issue in many regions and is defined by the concentration of dissolved minerals, primarily calcium and magnesium. These minerals originate from the earth, usually from limestone or chalky areas, dissolving as water travels over and through these rocks.
The presence of these minerals is what forms the "hard" qualities of the water. While not harmful to health, hard water can be a nuisance in households.
Problems associated with hard water include poor soap performance and the build-up of mineral scales in pipes and hot water heaters, which can reduce efficiency and cause damage over time.

Calcium Ions

Calcium ions (\(\mathrm{Ca}^{++}\)) are one of the primary culprits of water hardness. These positively charged ions dissolve in the water from natural sources.
In the context of water softening, calcium ions are exchanged with sodium ions during the ion exchange process.
When calcium ions are present in large amounts, they cause scale buildup in plumbing and reduce the efficiency of soaps. Removing calcium ions is a major target of water softening methods to improve water quality and usability.

Magnesium Ions

Magnesium ions (\(\mathrm{Mg}^{++}\)) are similar to calcium ions in that they contribute to water hardness. These ions typically stem from minerals like dolomite and can dissolve into water as it moves through the ground.
Just like calcium ions, magnesium ions can lead to similar problems of soap scum and pipe scale. Therefore, during the ion exchange process, these magnesium ions are often swapped out with more benign sodium ions.
Successfully removing magnesium ions is crucial to achieving soft water, which is more effective for cleaning and less damaging to appliances.