Problem 40 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following is the composition of carnalite? (a) \(\mathrm{Mg} \mathrm{Cl}_{2} . \mathrm{KCl}_{2} 6 \mathrm{H}_{2} \mathrm{O}\) (b) \(\mathrm{Fe}_{3} \mathrm{O}_{4}\) (c) \(\mathrm{Na}_{3} \mathrm{AIF}_{5}\) (d) \(\mathrm{Na}_{2} \mathrm{Al}_{2} \mathrm{O}_{3}\)

Step-by-Step Solution

Answer

Carnalite is composed of \( ext{MgCl}_2 imes ext{KCl}_{2} imes 6 ext{H}_2 ext{O}\), so option (a) is correct.

Step 1: Understand Carnalite

Carnalite is a mineral composed mainly of magnesium, potassium, and chlorine with water of crystallization. Its chemical formula is usually represented as \( ext{KMgCl}_3 imes 6 ext{H}_2 ext{O}\).

Step 2: Analyze Option (a)

Option (a) is \( ext{MgCl}_2 imes ext{KCl}_{2} imes 6 ext{H}_2 ext{O}\). This is close to the chemical formula for carnalite. The main components are magnesium, potassium, chlorine, and water of crystallization, which matches carnalite.

Step 3: Analyze Option (b)

Option (b) is \( ext{Fe}_3 ext{O}_4\), which is a form of iron oxide known as magnetite, not carnalite.

Step 4: Analyze Option (c)

Option (c) is \( ext{Na}_3 ext{AIF}_5\), which is sodium aluminum fluoride, also known as cryolite, not carnalite.

Step 5: Analyze Option (d)

Option (d) is \( ext{Na}_2 ext{Al}_2 ext{O}_3\), which does not represent carnalite. It neither contains magnesium nor the water molecules that characterize carnalite.

Step 6: Conclusion

From the analysis of all options, option (a) \( ext{MgCl}_2 imes ext{KCl}_{2} imes 6 ext{H}_2 ext{O}\) is the correct representation of carnalite, considering the compounds present and the presence of water of crystallization.

Key Concepts

Mineral Composition

Carnalite is a naturally occurring mineral with a unique composition. It is primarily made up of magnesium, potassium, and chlorine elements along with water of crystallization. This makes it a hydrous chloride mineral that forms in evaporite deposits. These minerals typically form by the evaporation of saline water.

• Magnesium - a key component known for making alloys and also vital for plant growth.
• Potassium - an essential nutrient for plants and a significant player in emotional and muscular function.
• Chlorine - in the mineral structure, it helps to balance the charges of the other ions.
• Water of crystallization - contributes to the formation of the crystalline structure of carnalite.

These elements come together as salts and water to form the crystalline mineral seen as carnalite, valued in various industries for its components.

Chemical Formula Analysis

Chemical formula analysis helps in identifying the distinct components that make up carnalite. The chemical formula of carnalite is often represented as \[\text{KMgCl}_3 \times 6 \text{H}_2 \text{O}\]which points out its composition.

• "K" stands for potassium, highlighting its essential role in the formula.
• "Mg" indicates the presence of magnesium.
• "Cl" signifies chlorine, contributing to the compound's salt base and overall stability.
• The "6H₂O" suggests six molecules of water are present in the crystalline structure.

Analyzing the chemical formula gives us detailed insight into the chemical interactions, stability, and characteristics that result from the combination of these elements in carnalite.

Water of Crystallization

Water of crystallization is an integral part of the structure and properties of carnalite, represented in the formula as 6\( \text{H}_2 \text{O} \). This water is not free-flowing but is incorporated into the mineral’s crystalline structure.

• It plays a crucial role in the formation and stabilization of carnalite's crystal lattice.
• Provides the mineral with certain properties like solubility and reactiveness.
• Helps in maintaining the mineral's integrity when subjected to changes in environmental conditions such as temperature and humidity.

The presence of water molecules is what classifies certain minerals as hydrates, impacting its physical properties and uses.

Magnesium Chloride

Magnesium chloride (MgCl₂) is a significant component of carnalite. It is a salt and exists in its crystalline form in carnalite through a bonding arrangement with potassium chloride and water of crystallization.

• Known primarily as a supplier of magnesium in various industries and applications.
• Plays a role in the extraction of magnesium, essential for various industrial processes.
• It's also an essential part of the electrolyte balance in the industry, particularly in chemical reactions and processes.
• Used in de-icing surfaces including roads, particularly in regions prone to icy winters.

Understanding MgCl₂ and its role within carnalite helps appreciate the importance of magnesium in different forms and applications beyond its basic elemental role.

Potassium Chloride

Potassium chloride (KCl) is another vital component of carnalite. Its presence is essential due to its numerous applications and properties.

• KCl contributes to the mineral's composition, making it essential in the agricultural sector as a fertilizer.
• It provides the potassium crucial for plant growth and soil nutrient balance.
• In the context of human and animal health, it plays a role in managing the body's potassium levels.
• KCl also finds usage in laboratory settings, for example, in chemical experimentations and reactions.

Its ionic structure with balanced positive and negative charges highlights its role in the carnalite’s composition, offering insights into its balanced nature and effectiveness in different uses.