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

Question

Halides of alkaline earth metals form hydrates such as \(\mathrm{MgCl}_{2} \cdot 6 \mathrm{H}_{2} \mathrm{O}, \quad \mathrm{CaCl}_{2} \cdot 6 \mathrm{H}_{2} \mathrm{O}, \quad \mathrm{BaCl}_{2} \cdot 2 \mathrm{H}_{2} \mathrm{O}\) 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 answer is (d) all of the above.

Step 1: Understanding Hydration

Halides of alkaline earth metals tend to form hydrates as they can incorporate water molecules into their structure. This ability to combine with water is due to their hygroscopic nature.

Step 2: Exploring Hygroscopic Nature

When a substance can absorb moisture from the air and form hydrates, it is considered hygroscopic. This is evident from the given hydrates: \( \mathrm{MgCl}_{2} \cdot 6 \mathrm{H}_{2} \mathrm{O} \), \( \mathrm{CaCl}_{2} \cdot 6 \mathrm{H}_{2} \mathrm{O} \), \( \mathrm{BaCl}_{2} \cdot 2 \mathrm{H}_{2} \mathrm{O} \), and \( \mathrm{SrCl}_{2} \cdot 2 \mathrm{H}_{2} \mathrm{O} \).

Step 3: Evaluating Dehydrating Properties

Many hygroscopic substances can also act as dehydrating agents because they remove water molecules from their surroundings. This can lead to them being used as such in certain applications.

Step 4: Reviewing Given Options

Let's analyze the provided options: (a) absorb moisture from air, (b) act as dehydrating agents, (c) are hygroscopic in nature, and (d) all of the above. Since hydrates indicate both that these halides absorb moisture (hygroscopic) and can dehydrate other substances, all options are linked.

Step 5: Concluding the Answer

Considering the nature of these halides, all options (a), (b), and (c) are applicable. Therefore, the correct answer is (d) all of the above.

Key Concepts

Hygroscopic Nature

The term "hygroscopic" refers to the ability of a substance to attract and hold water molecules from its surrounding environment. Alkaline earth metal halides such as \( \mathrm{MgCl}_{2} \cdot 6 \mathrm{H}_{2} \mathrm{O} \) and \( \mathrm{CaCl}_{2} \cdot 6 \mathrm{H}_{2} \mathrm{O} \) demonstrate this property by forming hydrates when exposed to moist air.
This hygroscopic nature is quite common among certain salts due to their polar nature, which easily attracts water molecules.
When these halides encounter moisture in the air, they readily absorb it, forming a stable hydrate structure. Hygroscopic substances can be useful in various applications, often as drying agents or in controlling humidity in products.

Dehydrating Agents

Dehydrating agents are substances that can remove water molecules from other materials or environments. They are frequently used in chemical processes and for preserving substances by preventing moisture-induced changes.
Alkaline earth metal halides like \( \mathrm{CaCl}_{2} \) are effective dehydrating agents. They can absorb moisture quickly, making them ideal for tasks like drying gases and liquids or keeping products dry during transportation.

• They work by drawing water molecules from their surroundings into their structure, where the water is securely held.
• This characteristic enables them to maintain reactive or anhydrous conditions in various industrial applications.

Group 2 Elements

Group 2 elements, also known as alkaline earth metals, include beryllium, magnesium, calcium, strontium, barium, and radium. These elements share several characteristics due to their position in the periodic table.
One significant property of group 2 elements is their tendency to form ionic compounds, such as halides with a characteristic hygroscopic nature.

• They typically have two electrons in their outermost shell, which they readily lose to achieve a stable electron configuration—this leads to the formation of \( 2^+ \) charges.
• Alkaline earth metals have notable reactivity, which increases as you move down the group.
• These elements are essential in various applications, from construction materials (like lime from calcium) to electronics and medical therapies.