Problem 108 - A Complete Resource Book in Chemistry for JEE Main

Question

When a 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

Step-by-Step Solution

Answer

The sodium ions are exchanged with (2) \(\mathrm{Ca}^{2+}\) ions and (4) \(\mathrm{Mg}^{2+}\) ions. Correct answer: (a) 2,4.

Step 1: Understanding Hard Water

Hard water typically contains high concentrations of metal cations, primarily calcium (\(\mathrm{Ca}^{2+}\)) and magnesium (\(\mathrm{Mg}^{2+}\)), which contribute to water hardness.

Step 2: What is Zeolite's Role?

Zeolites are used in water softening systems to remove hard ions such as calcium and magnesium. They work by exchanging sodium ions with the hard ions of water.

Step 3: Analyzing Ion Exchange

When hard water passes through a zeolite, the sodium ions \((\mathrm{Na}^{+})\) in the zeolite are exchanged with the calcium \((\mathrm{Ca}^{2+})\) and magnesium \((\mathrm{Mg}^{2+})\) ions present in the hard water.

Step 4: Selecting the Correct Options

Since calcium and magnesium ions are exchanged with sodium ions in zeolites, options (2) \(\mathrm{Ca}^{2+}\) ions and (4) \(\mathrm{Mg}^{2+}\) ions are correct. Hence, option (a) is the right choice.

Key Concepts

Zeolites

Zeolites are fascinating minerals, mainly composed of hydrated sodium aluminium silicate. They are incredibly useful in processes like water purification due to their unique ion-exchange properties. The structure of zeolites consists of a three-dimensional framework of silica and alumina, which creates cavities and channels. Within these spaces, you can find water molecules and exchangeable ions.

• The primary function of zeolites in water softening is to swap out sodium ions for calcium and magnesium ions, which are often responsible for hard water.
• This exchange ability comes from their porous nature, allowing them to trap and hold ions effectively.

The charm of zeolites lies in their ability to improve water quality. By having sodium ions ready to swap with harder ions, they can efficiently soften water. This exchange not only softens water but also prevents scale buildup in pipes and appliances, prolonging their lifespan.

Water Softening

Water softening is a vital process aimed at reducing water hardness, making it more suitable for everyday use. The presence of minerals like calcium and magnesium in hard water is what causes many issues, from soap inefficacy to scale buildup. By softening water, these problems can be significantly minimized.
In a typical water softening system, ion-exchange resins like zeolites play the leading role. As hard water passes through the zeolite bed, the sodium ions in the zeolite are swapped with calcium and magnesium ions in the water. This exchange transforms hard water into soft water, as it removes the hardness-causing ions.

• Softened water allows soap to lather more easily and effectively, reducing its consumption.
• It also helps in preventing mineral deposits, which can clog pipes and damage heating elements.

Through water softening, the efficiency of cleaning processes is improved, and the longevity of plumbing systems and appliances is enhanced.

Hard Water Chemistry

Hard water chemistry deals with understanding why water behaves the way it does when it contains high levels of calcium (\(\mathrm{Ca}^{2+}\)) and magnesium (\(\mathrm{Mg}^{2+}\)) ions. These ions originate from the dissolution of rocks and minerals as water flows through the environment.
The presence of these metal cations causes several issues:

• Limescale buildup in pipes and appliances, leading to decreased efficiency and possible damage.
• Reduced effectiveness of soaps and detergents, requiring more product to achieve desired cleaning results.

The chemistry behind hard water highlights the necessity of removing or reducing these hard ions. The ion exchange process is key to addressing this issue. By understanding hard water chemistry, it's easier to see the benefits of water softening and the role zeolites play in this process.