Which of the following laboratory procedures best illustrates the law of conservation of mass?

• A. Mixing vinegar and baking soda in an open flask and observing the release of gas.
• B. Burning magnesium ribbon in open air and measuring the mass of the ash produced.
• C. Heating a sealed container in which hydrogen and oxygen react to form water, and measuring the mass before and after the reaction.
• D. Evaporating water from an open beaker and measuring the mass of the remaining liquid.

Answer: (C)

Verified step by step guidance

1. Understand the law of conservation of mass, which states that mass cannot be created or destroyed in a chemical reaction; the total mass of reactants equals the total mass of products.
2. Analyze each procedure to see if the system is closed or open. In an open system, gases or substances can escape, causing mass changes that do not reflect the true conservation of mass.
3. Identify that mixing vinegar and baking soda in an open flask releases gas that escapes, so the mass measured will decrease, not illustrating conservation of mass accurately.
4. Recognize that burning magnesium in open air allows gases to escape, so the mass of ash alone will not equal the original mass, failing to demonstrate conservation of mass properly.
5. Note that heating a sealed container where hydrogen and oxygen react to form water keeps all substances contained, allowing measurement of mass before and after reaction to show mass remains constant, best illustrating the law of conservation of mass.