When a copper coin is coated to appear silver in a chemical reaction, how does the mass of the coin change?

• A. The mass increases because a layer of another substance is added to the coin.
• B. The mass remains exactly the same because no atoms are added or removed.
• C. The mass decreases because copper is converted into silver.
• D. The mass fluctuates randomly during the reaction.

Answer: (A)

Verified step by step guidance

1. Understand the nature of the chemical reaction: when a copper coin is coated to appear silver, a new substance (often silver or a silver compound) is deposited on the surface of the coin.
2. Recognize that adding a layer of another substance means atoms from outside the coin are being added onto it, which affects the total mass.
3. Recall the Law of Conservation of Mass, which states that mass is neither created nor destroyed in a chemical reaction, but the mass of the system can change if material is added or removed from the object itself.
4. Since the coin gains a layer of another substance, the total mass of the coin plus the coating increases because new atoms are physically added to the coin's surface.
5. Therefore, the mass of the coin increases due to the addition of the coating material, rather than remaining the same or decreasing.