Problem 144 - A Complete Resource Book in Chemistry for JEE Main

Question

Match the following: List-I 1\. Nichrome 2\. Type metal 3\. Wood's metal 4\. Devarda's alloy List-II (i) \(\mathrm{Pb}, \mathrm{Bi}, \mathrm{Sn}, \mathrm{Cd}\) (ii) \(\mathrm{Pb}, \mathrm{Sb}, \mathrm{Sn}\) (iii) \(\mathrm{Cu}, \mathrm{Al}, \mathrm{Zn}\) (iv) \(\mathrm{Fe}, \mathrm{Ni}, \mathrm{Cr}\)

Step-by-Step Solution

Answer

1.-(iv), 2.-(ii), 3.-(i), 4.-(iii)

Step 1: Understanding Nichrome

Nichrome is an alloy composed primarily of nickel and chromium. Thus, it matches with list-II option (iv) which is \( \mathrm{Fe}, \mathrm{Ni}, \mathrm{Cr} \).

Step 2: Understanding Type Metal

Type metal is traditionally an alloy used for making metal type, composed primarily of lead (Pb), antimony (Sb), and tin (Sn). Thus, it matches with list-II option (ii) \( \mathrm{Pb}, \mathrm{Sb}, \mathrm{Sn} \).

Step 3: Understanding Wood's Metal

Wood's metal is a fusible alloy with a low melting point, consisting mainly of lead (Pb), bismuth (Bi), tin (Sn), and cadmium (Cd). Therefore, it corresponds to list-II option (i) \( \mathrm{Pb}, \mathrm{Bi}, \mathrm{Sn}, \mathrm{Cd} \).

Step 4: Understanding Devarda's Alloy

Devarda's alloy is typically used in chemical analysis and is made up of copper (Cu), aluminum (Al), and zinc (Zn). Hence, it matches with list-II option (iii) \( \mathrm{Cu}, \mathrm{Al}, \mathrm{Zn} \).

Key Concepts

Nichrome Composition

Nichrome is a fascinating alloy widely recognized for its exceptional resistance to heat and oxidation. This remarkable material is primarily composed of nickel, chromium, and often iron (Fe). These metals come together to form an alloy that is incredibly durable and resistant to corrosion. Because of these properties, nichrome is often used in applications that require high temperatures and resistance to wear.

• Nickel (Ni): This element provides excellent corrosion resistance and contributes to the alloy's ability to withstand high temperatures without degrading.
• Chromium (Cr): Chromium enhances nichrome's hardness and durability. It forms a protective oxide layer on the surface, shielding the metal underneath.
• Iron (Fe): Sometimes included to enhance the structural integrity of the alloy.

Nichrome is commonly used in heating elements in appliances such as toasters and hair dryers. Its ability to maintain structural integrity under extreme heat makes it invaluable in many industrial processes.
Its unique properties arise from the way these elements interact at a molecular level, forming a robust material that performs excellently under demanding conditions.

Type Metal Components

Type metal is traditionally important in the printing industry for creating movable type for letterpress. This material is primarily an alloy of lead (Pb), antimony (Sb), and tin (Sn). Each component in this alloy contributes distinct properties that make it suitable for repetitive printing tasks.

• Lead (Pb): Provides the bulk and weight, making it easy to cast into shapes and providing longevity to the type.
• Antimony (Sb): Contributes hardness and durability, ensuring the type metal can withstand the pressure of printing presses without significant wear.
• Tin (Sn): Aids in creating a smooth casting process and provides a certain amount of flexibility.

The precise balance of these metals allows type metal to be easily recycled and recast, which is crucial in the dynamic world of traditional printing.
Despite being largely replaced by digital methods, the knowledge of type metal's composition offers insight into the technological advancements in metallurgy and manufacturing.

Wood's Metal Properties

Wood's metal is known for its exceptionally low melting point, which is much lower than many other alloys. This property makes it particularly useful in applications where a quick melt is required, such as in safety devices and sprue wax casting. The alloy is primarily composed of lead (Pb), bismuth (Bi), tin (Sn), and cadmium (Cd).

• Lead (Pb): Provides weight and volume to the alloy, making it more stable.
• Bismuth (Bi): Offers a low melting point, which is the key property of Wood's metal.
• Tin (Sn): Helps in alloying process and enhances fluidity when melted.
• Cadmium (Cd): Contributes to the fusibility of the alloy.

Wood's metal melts at around 70°C (158°F), which is notably lower compared to most common metals and alloys. This unique property allows it to be used in automatic fire sprinklers and other safety devices that need to trigger at a specific temperature.
The composition of Wood's metal reflects the innovative use of alloying techniques to harness specific characteristics, such as low melting points, for specialized applications.

Devarda's Alloy Usage

Devarda's alloy holds an important role in chemical analysis, particularly in the detection and measurement of nitrogen compounds. This alloy is composed of copper (Cu), aluminum (Al), and zinc (Zn), each providing unique benefits that make it ideal for use as a reducing agent in laboratory settings.

• Copper (Cu): Provides stability and contributes to the compound's overall conductivity.
• Aluminum (Al): Acts as the principal reducing agent, which is essential for its role in analytical chemistry.
• Zinc (Zn): Enhances the alloy's ability to act as a reducing agent.

The practicality of Devarda's alloy in reducing nitrate to ammonia makes it a useful tool in soil testing and environmental chemistry. This process is critical for scientists seeking to understand and manage nitrogen levels in agricultural and ecological systems.
The synergy between these metals within the alloy showcases the purposeful design of materials in scientific research to address specific analytical challenges.