Multiple Choice
Which of the following best describes the law of conservation of mass?
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2. Atoms & Elements
Law of Conservation of Mass
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In an experiment where magnesium is heated in air to form magnesium oxide, the final product has a greater mass than the original magnesium. According to the law of conservation of mass, where did the extra mass in magnesium oxide come from?
A
The balance used in the experiment was incorrectly calibrated.
B
Water vapor from the air was absorbed by the magnesium.
C
Magnesium atoms gained mass during heating.
D
Oxygen from the air combined with magnesium during the reaction.
Verified step by step guidance1
Recall the law of conservation of mass, which states that mass cannot be created or destroyed in a chemical reaction; it can only be rearranged.
Understand that when magnesium is heated in air, it reacts with oxygen to form magnesium oxide, a compound consisting of magnesium and oxygen atoms chemically bonded together.
Recognize that the increase in mass is due to the addition of oxygen atoms from the air combining with the magnesium atoms during the reaction.
Note that the mass of the final product (magnesium oxide) is the sum of the original mass of magnesium plus the mass of the oxygen that has combined with it.
Conclude that the extra mass observed is not from experimental error or absorption of water vapor, but from the oxygen atoms incorporated into the magnesium oxide.
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