Problem 43 - A Complete Resource Book in Chemistry for JEE Main

Question

Which one of the following metals 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

Copper (Cu) is found in all three alloys: gun metal, monel metal, and constantan.

Step 1: Identify the Composition of Gun Metal

Gun metal is a type of bronze that is typically made from copper (Cu), tin (Sn), and zinc (Zn). Copper is the primary component, making up around 88% of the alloy.

Step 2: Identify the Composition of Monel Metal

Monel metal primarily consists of nickel (around 67%) and copper (around 28%). It may also contain small amounts of iron, manganese, carbon, and silicon. Copper is the main metal along with nickel.

Step 3: Identify the Composition of Constantan

Constantan is an alloy typically composed of copper (55%) and nickel (45%). Copper is again a main component of this alloy.

Step 4: Determine the Common Metal

Now, examine the primary metals in each alloy. Gun metal, monel metal, and constantan all contain copper (Cu) as a significant component of their composition.

Key Concepts

Understanding Gun Metal Composition

Gun metal is a time-honored alloy known for its strength and resistance to corrosion, making it ideal for forging cannons and various engineering applications. The main component of gun metal is copper (Cu), which comprises about 88% of the alloy. This high percentage of copper gives gun metal its distinctive red-orange hue and excellent thermal and electrical conductivity.
In addition to copper, gun metal contains tin (Sn) and zinc (Zn). Tin, making up around 10%, adds hardness and wears resistance to the alloy, while zinc, at approximately 2%, increases its fluidity and strength.
Therefore, the combination of these metals results in a durable and versatile alloy used historically in weaponry and various modern applications such as valves, gears, and statues.

Exploring the Composition of Monel Metal

Monel metal is another alloy where copper plays a critical role, but in combination with nickel rather than tin and zinc. It's renowned for its exceptional resistance to corrosion, even by seawater, acids, and alkalies, which broadens its application range to uses like marine engineering, chemical processing, and aerospace.
The typical composition of monel is about 67% nickel and 28% copper. The presence of copper not only adds a layer of corrosion resistance but also enhances the alloy’s mechanical properties. Besides nickel and copper, monel can also include a small amount of iron, manganese, carbon, and silicon. These elements contribute to its strength and workability.
Monel’s unique combination of components provides it with superior strength and resistance to extreme conditions, making it one of the preferred materials in chemical and marine industries.

The Unique Features of Constantan

Constantan is a nickel-copper alloy notable for its high resistance to temperature change, making it perfect for use in thermocouples, electrical resistance wire, and precision resistors.
This alloy is composed of approximately 55% copper and 45% nickel. The major feature of constantan is its relatively neutral resistance to temperature, meaning its electrical resistance does not change significantly with temperature changes. This property is mainly due to the balanced ratio of copper and nickel.

• Copper in constantan ensures good conductivity and malleability.
• Nickel contributes to its corrosion resistance and mechanical strength.

Constantan's stable behavior under varying thermal conditions makes it indispensable for precise temperature measurement and electrical applications where accuracy is key.