Bronze is preferred to copper in the making of medals because it

Analysis

The question asks for the reason why bronze is preferred over pure copper for manufacturing medals. To answer this, we must look at the properties of pure metals versus alloys.

Concept Explanation

• Copper: Copper is a pure metal. In its pure state, the atoms are arranged in regular layers that can easily slide over one another when force is applied. This makes pure copper relatively soft and malleable.
• Bronze: Bronze is an alloy—a mixture of copper and tin. When tin is added to copper, the tin atoms (which are a different size) disrupt the regular arrangement of the copper atoms. This makes it much harder for the layers to slide over each other.
• Alloying: The primary purpose of creating alloys like bronze is to improve the mechanical properties of the base metal, specifically increasing its hardness and strength.

Step-by-Step Solution

1. Compare Properties: Pure copper is soft and easily deformed. Bronze, being an alloy, is significantly harder and more durable.
2. Evaluate Options: • A (is stronger): Because the atoms in the alloy are locked in place by the different-sized atoms of the alloying element (tin), the material is much stronger and more resistant to deformation than pure copper. This is the primary reason it is used for medals, which need to maintain their shape and detail over time. • B (can withstand low temperature): While true, this is not the primary reason for choosing bronze over copper for medals. • C (is lighter): Bronze is generally denser than copper because tin is a relatively heavy metal; therefore, it is not lighter. • D (has low tensile strength): This is incorrect. Alloys are specifically designed to have higher tensile strength than their constituent pure metals.

Conclusion

Bronze is chosen for medals because the alloying process makes it harder and more durable (stronger) than pure copper, ensuring the medals do not bend or scratch easily.

Exam Tip: Whenever you see a question about alloys (like Brass, Bronze, or Steel), always remember that the main goal of alloying is to increase strength and hardness and to prevent corrosion.