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

Question

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

Step-by-Step Solution

Answer

Option (a) \(\mathrm{MgCl}_{2} \cdot \mathrm{KCl} .6 \mathrm{H}_{2} \mathrm{O}\) is the composition of carnalite.

Step 1: Identify Carnalite

Carnalite is a mineral primarily composed of magnesium, potassium, and chloride. To solve this problem, we need to identify which option among the given contains these elements.

Step 2: Analyze Option (a)

Option (a) is \(\mathrm{MgCl}_{2} \cdot \mathrm{KCl} .6 \mathrm{H}_{2} \mathrm{O}\). This compound consists of magnesium chloride \(\mathrm{MgCl}_{2}\), potassium chloride \(\mathrm{KCl}\), and water molecules \((6 \mathrm{H}_{2} \mathrm{O})\). This combination matches the elements found in carnalite.

Step 3: Review Other Options

Option (b) is \(\mathrm{Fe}_{3} \mathrm{O}_{4}\), which is iron oxide; option (c) is \(\mathrm{Na}_{3} \mathrm{AlF}_{6}\), which is cryolite; and option (d) is \(\mathrm{Na}_{2} \mathrm{Al}_{2} \mathrm{O}_{3}\), which does not contain the required elements for carnalite. Therefore, they cannot be compositions of carnalite.

Step 4: Confirm the Correct Answer

Since option (a) contains magnesium, potassium, and chloride, it correctly represents the composition of carnalite. The presence of water molecules in this compound also corresponds to carnalite's hydrated nature.

Key Concepts

Carnalite Composition

Carnalite is a fascinating mineral known for its diverse makeup. It is primarily composed of magnesium, potassium, and chloride. This combination gives carnalite its unique properties.
To correctly identify carnalite's composition, we have to look for magnesium chloride (\(\mathrm{MgCl}_{2}\)) and potassium chloride (\(\mathrm{KCl}\)) alongside water molecules (\(\mathrm{6H}_{2}\mathrm{O}\))\.
No other combination will qualify as the true representation of carnalite, a mineral crucial in various industrial applications. Knowing the exact composition helps in the identification and utilization of this mineral in the field of inorganic chemistry.

Mineral Identification

Mineral identification is the process of determining the characteristics and composition of a mineral. This can be crucial in fields such as geology, chemistry, and material science.
To identify carnalite among other minerals, we engage in both visual and chemical examination. Visually, carnalite appears as a vitreous and often translucent mineral with a distinctive color ranging from pink to red.
This signifies its unique chemical composition. Chemically, we rely on the presence of elements such as magnesium, potassium, and chloride in the structure of the mineral. This method ensures precise identification.

• Examine the luster and color of the mineral
• Determine the chemical elements present
• Cross-check with known mineral compositions

This practice of attribution is essential for distinguishing carnalite from others like iron oxide, cryolite, or more commonly known salts.

Chemical Formulas

Chemical formulas are a simple way to represent the substance's make-up. For students learning about minerals, understanding formulas is critical.
The formula tells us the kinds and numbers of atoms in a compound. For example, carnalite's chemical formula (\(\mathrm{MgCl}_{2} \cdot \mathrm{KCl} \cdot 6 \mathrm{H}_{2}\mathrm{O}\)) reveals:

• Two chlorine atoms bonded with one magnesium atom
• One potassium atom bonded with a chloride ion
• Hydration with six water molecules

Each part of the chemical formula of carnalite conveys specific information. Understanding these chemical representations provides insights into the mineral's properties and helps in its classification and application.

Hydrated Compounds

Hydrated compounds like carnalite contain water molecules as part of their structure. These are often indicated in a formula by a dot followed by water as seen in (\(6 \mathrm{H}_{2} \mathrm{O}\)) within carnalite's composition.
Hydration gives minerals unique physical and chemical properties. In carnalite, these water molecules contribute to its solubility and crystalline structure.
These compounds can lose water content when heated; a process known as dehydration. Understanding the role of hydration is pivotal in industries where mineral solubility and thermal properties matter.

• Identifying whether a compound is hydrated
• Understanding how hydration affects properties
• Considering dehydration impacts

Thorough knowledge of hydrated compounds aids in many practical areas, from industrial applications to academic studies.