Problem 54 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following metal is found in gun metal, monel metal and constantan alloys? (a) \(\mathrm{Cu}\) (b) \(\mathrm{Fe}\) (c) \(\mathrm{Hg}\) (d) \(\mathrm{Zn}\)

Step-by-Step Solution

Answer

(a)  is found in all three alloys.

Step 1: Understanding the Alloys

First, let's understand what metals are typically found in each of the alloys mentioned: Gun metal, Monel metal, and Constantan. Gun metal is an alloy composed mainly of copper and tin. Monel metal consists primarily of nickel and copper. Constantan typically contains copper and nickel.

Step 2: Analyzing Alloy Composition

Let's list the compositions again, focusing on the primary components: Gun Metal: Copper and Tin, Monel Metal: Nickel and Copper, Constantan: Copper and Nickel. We notice a common metal across all three alloys.

Step 3: Identifying the Commonality

Looking at the compositions of gun metal, monel metal, and constantan, the common metal that appears in each alloy is copper (). Gun metal, monel metal, and constantan all contain copper as one of their key components.

Step 4: Choosing the Correct Option

Review the options provided: (a) , (b) , (c) , (d) . Copper is found in all three alloys we analyzed, so the correct answer is option (a) .

Key Concepts

Gun Metal

Gun metal is a type of bronze, a metal alloy known for its durability and ability to resist corrosion. It consists primarily of:

• Copper: Generally making up about 88% of the alloy. Copper gives gun metal its ability to conduct heat and electricity efficiently.
• Tin: Typically around 10-12%. Tin helps to improve the metal's resistance to wear and fatigue.
• Sometimes small amounts of zinc or lead: This can be included to enhance its machinability and strength.

This combination makes gun metal an excellent choice for various applications, including:

• Bearings
• Valves
• Pipes
• Hydraulic fittings

Traditionally, the name "gun metal" came from its historical use in making cannons, but today, it is appreciated for its robust mechanical properties and aesthetic appeal, frequently used in machinery and ornamental objects.

Monel Metal

Monel is another alloy known for its toughness under harsh conditions. The primary elements found in Monel are:

• Nickel: Makes up a substantial part, approximately 67-70% of the alloy, providing excellent resistance to corrosion.
• Copper: Generally around 20-29%, adding both malleability and some thermal and electrical conductivity.
• Other possible elements: Monel may also contain trace amounts of iron, manganese, carbon, and silicon to modify its properties.

Monel is often selected for:

• Marine applications, due to its excellent resistance to seawater
• Chemical processing equipment
• Aerospace engineering components
• Musical instruments

The versatility and resilience of Monel make it a valuable choice for situations requiring both durability and reliability in corrosive environments.

Constantan

Constantan is yet another valuable alloy, designed primarily with one key feature in mind: its electrical properties. The composition of Constantan is as follows:

• Copper: Typically 55-60%, contributing to the alloy's low thermal conductivity and high malleability.
• Nickel: Generally around 40-45%, offering excellent resistance against oxidization and corrosion.

Constantan stands out for its use in:

• Thermocouples, as it has a consistent electrical resistance across a wide temperature range
• Low-temperature applications, such as cryogenic systems
• Resistive wire in electronic components

Electrical engineers and designers often choose Constantan for precision work because its resistivity remains stable over a broad range of temperatures, ensuring reliable performance in sensitive equipment.