Problem 65 - A Complete Resource Book in Chemistry for JEE Main

Question

Carnalite on electrolysis gives (a) \(\mathrm{Na}\) and \(\mathrm{CO}_{2}\) (b) \(\mathrm{Mg}\) and \(\mathrm{Cl}_{2}\) (c) \(\mathrm{Al}\) and \(\mathrm{Cl}_{2}\) (d) \(\mathrm{Ca}\) and \(\mathrm{Cl}_{2}\)

Step-by-Step Solution

Answer

(b) \( \mathrm{Mg} \) and \( \mathrm{Cl}_{2} \)

Step 1: Identify Carnalite

Carnalite is a mineral with the chemical formula \( KCl \cdot MgCl_2 \cdot 6H_2O \), composed of potassium chloride and magnesium chloride.

Step 2: Understand Electrolysis Output

Upon electrolysis, carnalite primarily decomposes to give products from its main components, which are magnesium chloride and potassium chloride.

Step 3: Determine Products of Electrolysis

The electrolysis of magnesium chloride, \( MgCl_2 \), results in the formation of magnesium metal \( Mg \) and chlorine gas \( Cl_2 \).

Step 4: Match with Options

From the given options, (b) \( \mathrm{Mg} \) and \( \mathrm{Cl}_{2} \) matches the products obtained from the electrolysis of carnalite, focusing on magnesium chloride.

Key Concepts

Carnalite

Carnalite is a fascinating mineral that consists of a unique mixture of potassium chloride (KCl) and magnesium chloride (MgCl₂) tied together with water molecules. Specifically, it has the chemical formula \( KCl \cdot MgCl_2 \cdot 6H_2O \). This mineral is an important source of magnesium, which is a lightweight metal used in various applications. Being a double salt, carnalite occurs naturally and is often found in evaporite deposits along with other minerals like halite and sylvite. The presence of water molecules is what helps carnalite readily dissolve in water, making the extraction of its components practical through the process of electrolysis. By understanding the composition and properties of carnalite, we can see why it plays a crucial role in the production of magnesium and other industrially important compounds.

Magnesium Chloride

Magnesium Chloride, \( MgCl_2 \), is a critical compound in the process of electrolysis for obtaining pure magnesium metal. It is usually derived from natural resources like seawater and brine solutions, and also from minerals such as carnalite. When magnesium chloride undergoes electrolysis, this chemical reaction breaks it down into magnesium metal and chlorine gas as products. - The chemical equation for this electrolysis can be represented as: \[ \text{MgCl}_2 \xrightarrow{\text{Electrolysis}} \text{Mg} + \text{Cl}_2 \]As a result, chlorine is collected as a gas, while magnesium is obtained in its pure, metallic form. This method is highly efficient and utilizes magnesium chloride's ability to easily lose its chloride ions during the reaction. Given its importance, \( MgCl_2 \) is not just central to metallurgy but also has widespread use in de-icing roads and in pharmaceutical industries.

Chemical Reactions

Chemical reactions are processes where substances, known as reactants, transform into different substances called products. In the context of carnalite and its component magnesium chloride, chemical reactions are central to extracting valuable products under specific conditions.- **Electrolysis as a Chemical Reaction:** Electrolysis is a powerful chemical reaction technique used to decompose substances. By applying an electric current to a compound, like \( MgCl_2 \), it splits into magnesium and chlorine gas.- **Redox Reactions in Electrolysis:** During electrolysis, reduction and oxidation (redox) occur. The reduction takes place at the cathode, where magnesium ions gain electrons to become magnesium metal. Oxidation happens at the anode, where chloride ions lose electrons to form chlorine gas. This entire process showcases the intricate nature of chemical reactions, where energy input leads to the formation of new products, serving both industrial and practical purposes.