Standard level
Reactions occur when particles, atoms, molecules or ions collide. These collisions can only occur at the surface of a solid, so the grain size of the solid has an impact on the rate.
Background
Marble is a type of metamorphic rock, formed when limestone, calcium carbonate, is subject to high pressure and temperature under the ground.
Calcium carbonate reacts with hydrochloric acid forming a solution of calcium chloride and releasing carbon dioxide gas.
Calcium carbonate + hydrochloric acid
CaCO3(s) + 2HCl(aq) → CaCl2(aq) + CO2(g) + H2O(l)
Carbon dioxide is released as a gas and the overall mass of the reaction mixture decreases. This allows us to monitor the extent of the reaction by performing it on a top-pan electronic balance.
Chemicals
- Marble chips separated into 3 chip sizes
- Hydrochloric acid, 2.0 mol dm-3
Apparatus
- Conical flask, 250ml
- Measuring cylinder, 50ml
- Top-pan balance
- Stopwatch
- Using only small marble chips, accurately weigh out about 2g.
- Measure out 50cm3 of the bench hydrochloric acid into a conical flask.
- Weigh the flask and contents with a loose cotton wool plug (prevents splashing).
- Leaving the flask on the top-pan balance, add the marble chips, equickly replacing the cotton wool plug and start the stopwatch.
- Record the mass every 20 seconds.
- Hydrochloric acid is corrosive