Question

A student performs a reaction between hydrochloric acid (HCl) and sodium bicarbonate (NaHCO₃) in a sealed container. The balanced chemical equation for the reaction is:

HCl (aq)+NaHCO₃ (s)→NaCl (aq)+H₂O (l)+CO₂ (g)
Before the reaction, the total mass of the sealed container and its contents is measured to be 120.0 grams. After the reaction is complete, the student notices bubbling inside the container (gas formation), but the container remains sealed. The total mass is measured again and is still 120.0 grams.

What does this result demonstrate about the law of conservation of mass?

(1 point)
Responses

Mass was lost during the reaction because a gas was produced.
Mass was lost during the reaction because a gas was produced.

Mass was gained during the reaction because water was formed.
Mass was gained during the reaction because water was formed.

Mass was conserved because the sealed system prevented gas from escaping.
Mass was conserved because the sealed system prevented gas from escaping.

Mass changed because chemical reactions always absorb or release energy.

Answer 1

Mass was conserved because the sealed system prevented gas from escaping.

Explanation: The CO2 produced remained inside the sealed container, so the total mass of reactants plus products stayed the same, demonstrating the law of conservation of mass.