Problem 51 - A Complete Resource Book in Chemistry for JEE Main

Question

An important ore of magnesium is (a) malachite (b) cassiterite (c) carnalite (d) galena

Step-by-Step Solution

Answer

The important ore of magnesium is (c) carnalite.

Step 1: Identify Magnesium Ores

Recognize that the question asks for an ore of magnesium. It's important to know which ores are identified with magnesium. Commonly known ones include magnesite and carnalite, among others. In this given list, your task is to determine which option is known for containing magnesium.

Step 2: Evaluate Each Option

Examine each given option: - (a) Malachite is primarily a copper carbonate hydroxide and doesn't contain magnesium. - (b) Cassiterite is primarily a tin oxide mineral, not associated with magnesium. - (c) Carnalite is a double salt with significant potassium and magnesium chloride composition. - (d) Galena is a lead sulfide mineral, with no magnesium content.

Step 3: Choose the Correct Answer

Based on the evaluation, carnalite is identified as an ore of magnesium. It contains magnesium chloride and is also a source of potassium.

Key Concepts

Carnalite

Carnalite is a fascinating mineral and an important ore of magnesium. It is a double salt composed of potassium chloride and magnesium chloride hexahydrate, with the chemical formula KCl · MgCl₂ · 6H₂O. This makes carnalite unique in its structure and significant for its roles in various industrial applications.

**Why is Carnalite Important?**
Carnalite is valuable because it's a source of both magnesium and potassium, two essential elements. Magnesium is widely used in industries for its light weight and strength. For instance, it is used in manufacturing aircraft, automobiles, and electronics. Potassium, on the other hand, is crucial for agricultural purposes as it is a key ingredient in fertilizers.

**Natural Occurrence**
Carnalite is typically found in sedimentary evaporite deposits where large amounts of water have evaporated, leaving behind concentrated minerals. Such environments help in forming extensive carnalite deposits, often along with other salts like halite and sylvite.

Magnesite

Magnesite, another essential magnesium ore, is mainly composed of magnesium carbonate, with the formula MgCO₃. Visually, magnesite can appear in different forms, ranging from white to grayish or yellowish colors.

**Magnesite in Industry**
The use of magnesite is prominent in the production of refractory materials due to its excellent heat resistance. These materials are essential for lining furnaces in industries that involve high-temperature processing, like steel manufacturing.

Additionally, magnesite serves as a source for producing magnesium oxide, a primary ingredient in cement and various chemical applications.

**Deposits and Extraction**
Magnesite deposits are usually present in ultramafic and ultrabasic rocks, where it forms through the alteration of minerals like olivine and serpentine. The extraction of magnesite involves mining these deposits, followed by crushing and calcination, a process that removes carbon dioxide, thus transforming it into magnesium oxide.

Magnesium Chloride

Magnesium chloride, often harvested from carnalite or directly from sea water, is a versatile compound with the formula MgCl₂. It is highly soluble in water and has essential uses across various fields.

**Industrial Uses**
Magnesium chloride is commonly used to produce magnesium metal. The production process involves the electrolysis of magnesium chloride, a method that extracts pure magnesium for use in lightweight and strong metal alloys.

In the food industry, magnesium chloride acts as a coagulant in the preparation of tofu and similar products. Its role in medicine includes its use as a magnesium supplement for treating deficiencies.

**Environmental and Other Uses**
This compound is also utilized for dust control and stabilization of dirt roads, given its hydrophilic nature, which helps to bind dust particles effectively. Furthermore, magnesium chloride serves as a de-icing agent, proving useful for melting ice on roads in winter climates.

The versatile nature of magnesium chloride highlights its crucial role in everyday products and industrial processes, making it an invaluable resource.