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

Option (b): 88% copper, 10% tin, 2% zinc.

Step 1: Understanding Gun Metal Composition

Gun metal, also known as red brass, is an alloy primarily composed of copper, tin, and zinc. To find the correct composition, we need to understand the typical percentages of each of these elements in gun metal.

Step 2: Identify the Typical Composition

Gun metal is generally composed of around 88% copper, 10% tin, and 2% zinc. This is the commonly accepted standard composition for gun metal.

Step 3: Compare Options

Given the options, we need to compare the typical composition with the provided values: - Option (a) 88% copper, 2% tin, 10% zinc - Option (b) 88% copper, 10% tin, 2% zinc - Option (c) 80% copper, 20% tin, 0% zinc - Option (d) 80% copper, 0% tin, 20% zinc

Step 4: Select the Correct Option

From our comparison: - Option (b) directly matches with the typical composition of gun metal, which is 88% copper, 10% tin, and 2% zinc.

Step 5: Conclusion

Thus, the correct percentages that match the standard composition of gun metal are in option (b).

Key Concepts

Copper Percentage

Copper is the primary element in the composition of gun metal, a type of bronze. It plays a significant role in determining the properties and appearance of the alloy. Typically, gun metal contains about 88% copper. This high concentration of copper gives the alloy its distinctive red-gold color, often leading to its nickname, "red brass."
Copper contributes to the alloy's excellent corrosion resistance, making it suitable for use in environments where it might be exposed to water or chemicals. This feature is particularly beneficial for items like ship fittings and bearings. Furthermore, copper's high thermal and electrical conductivity make gun metal ideal for applications requiring effective heat or electricity transfer. When studying gun metal, it's essential to remember its key characteristic lies in having a large proportion of copper, which influences both its mechanical properties and applications.

Tin Percentage

Tin is another essential component of gun metal, although present in a much lower percentage compared to copper. Typically, tin makes up about 10% of the alloy. Even in this small amount, tin significantly enhances the alloy's properties.
Incorporating tin into gun metal increases the material's overall strength and hardness. This makes the alloy durable and suitable for various industrial applications where mechanical stress might occur, such as gears and valve components. Tin also contributes to the alloy's corrosion resistance, a vital property for parts exposed to harsh environments or extreme conditions.
The presence of tin leads to the development of a superior surface finish, often valued in the manufacturing of precision instruments and aesthetic items. Therefore, while its percentage is relatively low, tin plays a crucial role in determining gun metal's quality and usability.

Zinc Percentage

Zinc is the third component of gun metal but is present in the smallest proportion—around 2%. This small addition of zinc has specific functions that enhance the metal's characteristics.
Zinc's primary role in the alloy is to improve its casting properties. It allows for a more fluid mixture when molten, assisting in filling complex mold shapes more effectively without compromising the integrity of the final product. This property is particularly useful in creating intricate parts where detail is crucial.
Moreover, zinc also enhances the alloy's wear resistance, making it suitable for components that undergo a lot of friction during their lifespan. Even though zinc is only a minor part of the composition, its inclusion is vital in ensuring the alloy's versatility and application in various fields.