Interactive: conservation of mass in a reaction. Marble chips react with hydrochloric acid in a flask on a balance. Run the reaction and switch between a stoppered, sealed flask and an open beaker, while a graph tracks the balance reading and the volume of carbon dioxide made.
Mass that seems to vanish has just escaped
Drop 1.00 g of marble chips into hydrochloric acid and the balance reading falls. Seal the flask and the reading does not budge, because the carbon dioxide is trapped instead of drifting away. Run the reaction and watch the balance, then switch between a sealed flask and an open beaker.
Weigh the reaction
Live · 35% reacted
CaCO₃(s) + 2HCl(aq) → CaCl₂(aq) + H₂O(l) + CO₂(g) · run it and watch the balance
Sealed · mass holds at 151.00 g
Balance reading
151.00 g
start 151.00 g · change 0.00 g
CO₂ gas made
87 mL
0.15 g · 0.0035 mol
Know This
In a closed system the total mass never changes, so any drop on an open balance equals the mass of gas that escaped, which you can check against the gas volume collected.