Which method allows a student to verify that a chemical reaction demonstrates the law of conservation of mass?

• A. Check if the temperature of the reaction mixture increases.
• B. Determine if a gas is produced during the reaction.
• C. Observe if the color of the substances changes during the reaction.
• D. Measure the mass of all reactants and products before and after the reaction to confirm that the total mass remains unchanged.

Answer: (D)

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; therefore, the total mass of reactants must equal the total mass of products.
2. Recognize that observing changes such as temperature increase, gas production, or color change does not directly measure mass and thus cannot confirm the conservation of mass.
3. Identify that the correct method to verify the law is to measure the mass of all reactants before the reaction begins.
4. Next, measure the mass of all products after the reaction is complete, ensuring that no substances are lost or gained from the system.
5. Compare the total mass of reactants and products; if they are equal within experimental error, this confirms that the chemical reaction demonstrates the law of conservation of mass.