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?

Question

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

Answer 1

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

3. The reaction produced a gas that escaped the beaker.

This option explains that during the mixing of the liquids, a gas was produced, which could have escaped into the atmosphere, leading to a decrease in mass of the combined liquid compared to the individual masses of the liquids prior to the reaction. This situation illustrates that while the mass of the reactants appears to decrease, matter is actually conserved overall; it has just changed states (from liquid to gas) and escaped from the system being measured.