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

Question

The percentage of copper, tin and zinc metals present in 'Gun metal' respectively are (a) \(88,2,10\) (b) \(88,10,2\) (c) \(80,20,0\) (d) \(80,0,20\)

Step-by-Step Solution

Answer

The correct answer is (b) 88% copper, 10% tin, 2% zinc.

Step 1: Understand Gun Metal Composition

Gun metal is an alloy that consists of copper, tin, and zinc. A typical composition is known to be high in copper content, with smaller amounts of tin and zinc.

Step 2: Analyze Each Option

Review each option's percentage of copper, tin, and zinc: - Option (a): Copper 88%, Tin 2%, Zinc 10% - Option (b): Copper 88%, Tin 10%, Zinc 2% - Option (c): Copper 80%, Tin 20%, Zinc 0% - Option (d): Copper 80%, Tin 0%, Zinc 20%.

Step 3: Determine Typical Composition for Gun Metal

Gun metal typically contains around 88% copper, 10% tin, and 2% zinc. This composition is chosen for its corrosion resistance and ease of machining, which are important properties for gun metal usage.

Step 4: Match with Options

Compare the typical composition of gun metal with the given options. Option (b) with 88% copper, 10% tin, and 2% zinc matches the typical composition of gun metal.

Key Concepts

Copper Composition

Copper is the primary metal in many alloys, such as gun metal. It constitutes about 88% of the composition of gun metal. The high copper content is crucial for several reasons:

• Conductivity: Copper is known for its excellent thermal and electrical conductivity, making it valuable in various applications.
• Strength: The metal provides an essential base strength that gives the alloy its robustness and durability.
• Color: The copper contributes to the characteristic reddish appearance of gun metal, which can be aesthetically pleasing.

Copper is thus integral to the core characteristics of gun metal, affecting its physical and chemical properties significantly.

Tin Composition

Tin is another important component of gun metal, usually making up around 10% of the mixture. This small percentage has a significant effect:

• Machinability: Tin enhances the alloy's ability to be easily formed or shaped without losing strength or framework.
• Corrosion Resistance: By adding tin, the alloy gains superior resistance to corrosion, which is critical when used in hostile environments.
• Hardness: Tin contributes to the hardness and wear resistance of the alloy, making it suitable for heavy-duty applications.

In summary, tin plays a vital role in enhancing the mechanical properties of gun metal.

Zinc Composition

Zinc, although only about 2% of the composition in gun metal, plays a complementary role. It assists in:

• Fluidity: Zinc helps improve the fluidity of the molten alloy, making it easier to cast complex shapes.
• Cost: Including zinc can also reduce the overall cost of the alloy as it's more economical than copper or tin.
• Properties Balance: Zinc contributes to the overall balance of mechanical properties, like tensile strength and flexibility.

Thus, even in small amounts, zinc provides notable benefits to the alloy structure.

Metal Alloys

Metal alloys are materials made by combining two or more metals to achieve superior properties compared to individual metals. Gun metal is a specific type of alloy known for its

• Hardness: Created by the combination of copper, tin, and zinc, it features enhanced hardness and strength.
• Versatility: Alloys like gun metal can be tailored to specific applications, ranging from bearings to other intricate components.
• Improved Properties: By altering the percentage of each metal, different characteristics and efficiencies for diverse applications can be achieved.

Alloys exemplify how metals can be combined to tailor their properties according to specific needs and applications.

Corrosion Resistance in Alloys

One of the standout qualities of gun metal is its corrosion resistance. This property is particularly valuable in environments that can cause deterioration in metals over time:

• Long-lasting Components: High corrosion resistance ensures the longevity and durability of components made from gun metal.
• Wide Application Range: This quality allows gun metal to be used in a myriad of environments, including marine and industrial contexts where corrosion is a significant factor.
• Economic Advantages: The reduced maintenance and replacement costs make it a cost-effective choice in the long run.

Corrosion resistance is a critical factor when choosing a material for specific functions, making gun metal a preferred choice for many applications.