Which of the following experiments best demonstrates that mass is conserved during a chemical reaction?

• A. Evaporating water from an open beaker and measuring the mass of the remaining liquid.
• B. Mixing salt and water in an open container and tasting the solution.
• C. Heating copper wire in open air and observing the color change.
• D. Reacting vinegar (acetic acid) with baking soda (sodium bicarbonate) in a sealed flask and measuring the mass before and after the reaction.

Answer: (D)

Verified step by step guidance

1. Understand the Law of Conservation of Mass, which states that mass is neither created nor destroyed in a chemical reaction; the total mass of reactants equals the total mass of products.
2. Identify that to demonstrate this law experimentally, the system must be closed so that no matter can enter or leave during the reaction.
3. Evaluate each experiment to see if it uses a closed system and allows measurement of mass before and after the reaction without loss of material.
4. Recognize that evaporating water or heating substances in open containers allows mass to escape (e.g., as vapor or gas), so mass measurements will not reflect conservation accurately.
5. Conclude that reacting vinegar with baking soda in a sealed flask is the best experiment because the flask prevents gas from escaping, allowing accurate measurement of mass before and after the reaction, thus demonstrating mass conservation.