Question

A student combines two liquids in a beaker. She observes that the mass of the combined liquid is less than the mass of the two separate liquids. The student claims that this observation shows that matter is not conserved in chemical reactions. Which statement explains why the student's claim is incorrect?

• The reaction did not change the physical properties of the liquids.
• The combined liquid was warmer than the two separate liquids.
• The product contained fewer atoms than the reactants.
• The reaction produced a gas that escaped the beaker.

Answer 1

The correct statement that explains why the student's claim is incorrect is:

• The reaction produced a gas that escaped the beaker.

This is because if a gas was released during the mixing of the liquids, some of the mass would have escaped into the environment, leading to a lower measured mass of the combined liquids in the beaker. This does not indicate that matter is not conserved; rather, it shows that mass was lost from the system due to the release of gas.