A solid and a solution react in a flask to produce a gas. The flask is sealed with a large flexible balloon and the whole apparatus is placed on a balance. The balloon expands during the first 2 minutes and then remains partly inflated at the same size. The balance reading remains at 186.42 g throughout. Which statement best explains these results?
The gas in the balloon is not weighed, but the products in the flask weigh more than the reactants.
Gas slowly escapes through the balloon, and the same mass of air enters the flask to replace it.
Gases have no mass, so the reading stays the same even though gas is still being made.
No atoms can enter or leave the apparatus, and the reaction finishes within the first 2 minutes.
95 exam-style questions on AQA GCSE Chemistry 3.1 Chemical measurements, conservation of mass and the quantitative interpretation of chemical equations, covering 3.1.1 Conservation of mass and balanced chemical equations, 3.1.2 Relative formula mass, 3.1.3 Mass changes when a reactant or product is a gas, and 3.1.4 Chemical measurements. Each one has a worked solution and a mark scheme showing where the marks go.