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

Question

Halides of alkaline earth metals form hydrates such as \(\mathrm{MgCl}_{2} \cdot 6 \mathrm{H}_{2} \mathrm{O}, \quad \mathrm{CaCl}_{2} \cdot 6 \mathrm{H}_{2} \mathrm{O}, \quad \mathrm{BaCl}_{2} .2 \mathrm{H}_{2} \mathrm{O}\) and \(\mathrm{SrCl}_{2} 2 \mathrm{H}_{2} \mathrm{O} .\) 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

(d) All of the above.

Step 1: Understand the problem

We are given the hydration states of halides of group 2 elements such as MgCl\(_2\), CaCl\(_2\), BaCl\(_2\), and SrCl\(_2\) with associated water molecules, forming hydrates. We need to determine the correct property of these hydrates from the options provided.

Step 2: Define key terms

Identify key terms: "Hygroscopic" refers to the ability to absorb moisture from the air, while "dehydrating agents" are substances that can remove water from other substances or compounds. "Absorb moisture from air" refers to the capacity of a substance to take up water vapor directly from the atmospheric moisture.

Step 3: Analyze each hydrate

Halides in the question, such as MgCl\(_2\), CaCl\(_2\), BaCl\(_2\), and SrCl\(_2\), are known to form hydrates, which indicates that these compounds incorporate water molecules into their crystal structure. This property means they absorb moisture from the air.

Step 4: Check if they are hygroscopic

Given that these halides naturally form hydrates by absorbing water, they demonstrate hygroscopic behavior, which matches option (c) stating they are hygroscopic in nature.

Step 5: Consider dehydrating agent properties

Dehydrating agents work by absorbing moisture, thereby acting as a moisture remover, which is consistent with these compounds' behavior of absorbing water from the atmosphere and thus can act as dehydrating agents, supporting options (b) and (d).

Step 6: Conclude with the best choice

Since these compounds absorb moisture, act as dehydrating agents, and show hygroscopic properties, option (d) "all of the above" accurately describes the properties exhibited by the hydrates of alkaline earth metal halides.

Key Concepts

Hydrates

In the study of chemistry, particularly concerning alkaline earth metal halides, hydrates play a significant role. Hydrates are compounds that include water molecules within their solid structure. These water molecules are not just bonded physically; they are an integral part of the crystals themselves. Imagine these water molecules as a glue holding the compound together, adding to its stability and uniqueness. For example, magnesium chloride (\(\mathrm{MgCl}_2\)) and calcium chloride (\(\mathrm{CaCl}_2\)) can each form hydrates with six water molecules (\(\cdot 6 \mathrm{H}_2 \mathrm{O}\)).These hydrates are formed because the compounds are strongly attracted to water molecules. An interesting fact is that not all compounds can form hydrates; only those with a high affinity for water are capable of doing so. The hydration process can significantly change the physical properties of a compound, such as its color, melting point, and solubility. This is why understanding hydrates is crucial in both chemistry and industry, as they influence how substances react and behave under different conditions.

Hygroscopic Behavior

Hygroscopic behavior is a fascinating property seen in some substances, particularly where alkaline earth metal halides are concerned. A hygroscopic substance has a natural ability to absorb water from the surrounding environment. Think of it as a sponge-like behavior on a molecular level. This means when you place a hygroscopic substance in a humid atmosphere, it will naturally attract and hold onto water molecules from the air.Some common examples of hygroscopic substances include the halides mentioned previously, such as \( \mathrm{MgCl}_2 \) and \( \mathrm{CaCl}_2 \). These compounds tend to pull in water vapor, forming hydrates as a result. Their hygroscopic behavior is so pronounced that if left exposed to air, they can easily transform by absorbing excess moisture.Understanding hygroscopic properties is important in different fields, from chemistry to meteorology, as it impacts everything from how substances are stored to their potential use in removing moisture from the air. This property is even exploited in everyday products like desiccants, which are used to keep things dry.

Dehydrating Agents

Dehydrating agents serve a vital function by removing water from other substances. When we talk about alkaline earth metal halides, these compounds often play the role of dehydrating agents due to their hygroscopic nature. By absorbing water, they effectively remove moisture from their surroundings or from other compounds.Consider \( \mathrm{CaCl}_2 \) as an example. This compound is regularly used in labs and industrial settings to dehydrate other chemicals by pulling water out of them. This property is extremely useful in chemical reactions and processes that require dry conditions to proceed accurately. Using dehydrating agents like \( \mathrm{CaCl}_2 \) not only helps in executing precise chemical reactions but also in preserving items that could be damaged by moisture. They can extend the shelf life of perishable goods and are invaluable in many scientific and industrial scenarios. Their ability to maintain a controlled environment by managing moisture levels highlights their importance in both practical and theoretical chemistry fields.