Problem 97 - A Complete Resource Book in Chemistry for JEE Main

Question

Halides of alkaline earth metals form hydrates such as \(\mathrm{MgCl}_{2} .6 \mathrm{H}_{2} \mathrm{O}, \quad \mathrm{CaCl}_{2} \cdot 6 \mathrm{H}_{2} \mathrm{O}, \quad \mathrm{BaCl}_{2} \cdot 2 \mathrm{H}_{2} \mathrm{O}\) and \(\mathrm{SrCl}_{2} \cdot 2 \mathrm{H}_{2} \mathrm{O} .\) This shows that halides of group 2 elements (a) can absorb moisture form air (b) act as dehydrating agents (c) are hydroscopic in nature (d) all of the above

Step-by-Step Solution

Answer

The correct choice is (d) all of the above.

Step 1: Understanding Hydrates

Halides of alkaline earth metals form compounds with water, known as hydrates. For example, magnesium chloride forms the compound \(\mathrm{MgCl}_{2} .6 \mathrm{H}_{2} \mathrm{O}\). Hydrates have water molecules attached, showing their ability to interact with water.

Step 2: Analyzing Moisture Absorption

Since these halides form hydrates by combining with water, they have the ability to absorb moisture from the air. This property is critical for substances to form hydrates.

Step 3: Exploring Dehydrating Agents

As hydrates release water when heated, these halides can also remove water from other substances, acting as dehydrating agents. This property is used frequently in chemical reactions.

Step 4: Understanding Hygroscopic Nature

A hygroscopic substance is one that can absorb moisture from the air. Given halides of alkaline earth metals form hydrates by absorbing water, they are hygroscopic.

Step 5: Combining All Observations

Considering the ability of these halides to absorb moisture, act as dehydrating agents, and their hygroscopic nature, we conclude that the halides of group 2 elements fulfill all the given properties.

Key Concepts

Moisture Absorption

Halides of alkaline earth metals have a fascinating ability to absorb moisture from the air. This moisture absorption plays a vital role in the formation of hydrates. The process begins when halides come into contact with moisture in the air. Due to their chemical structure, these metals effectively interact with water molecules, leading to the formation of hydrates.
The absorbed water molecules attach to the halide ions and form a crystalline structure.
Here are some examples:

• Magnesium chloride forms \(\mathrm{MgCl}_{2} .6 \mathrm{H}_{2} \mathrm{O}\)
• Calcium chloride becomes \(\mathrm{CaCl}_{2} \cdot 6 \mathrm{H}_{2} \mathrm{O}\)
• Barium chloride changes to \(\mathrm{BaCl}_{2} \cdot 2 \mathrm{H}_{2} \mathrm{O}\)

This ability to absorb moisture is crucial for various applications, including preventing hydration and aiding in chemical storage.

Dehydrating Agents

Halides of alkaline earth metals are not just good at absorbing moisture; they can also act as effective dehydrating agents. When these compounds are heated, they release the absorbed water. This property is known as dehydration.
By losing water molecules, the compounds can create dry conditions needed for certain chemical processes. This makes them useful in laboratories and industries where moisture needs to be controlled.
These same compounds can help remove water from other materials. Here are a few practical applications:

• Industrial drying processes
• Preparation of anhydrous chemicals, which are substances without water
• Use in drying gas streams

In essence, the ability to remove water makes these compounds invaluable in settings where moisture is detrimental.

Hygroscopic Properties

The hygroscopic nature of halides means they have a natural tendency to attract and hold water molecules from the surrounding environment. This occurs because moisture in the air is naturally attracted to the charged ions present in these halide compounds.

Hygroscopic substances are important in various fields for their moisture-attracting properties. Here's how they can be utilized:

• As moisture-reducing agents, especially in packaging, to protect products from humidity
• In humidity control systems, maintaining optimal levels of moisture for certain industrial processes
• As additives in products such as hand creams or lotions, where moisture retention is desired

These properties reveal why compounds with hygroscopic characteristics, like halides of alkaline earth metals, are so important in both everyday life and scientific applications.