Investigation: rate of reaction and factors affecting it

Aim: to investigate how concentration, temperature and surface area affect the rate of a reaction.

• Apparatus: sodium thiosulphate and hydrochloric acid (or marble chips), conical flask, stopwatch, thermometer.
• Method: change ONE variable at a time and time how long the reaction takes to reach a fixed endpoint.
• Rate is proportional to 1/time — plot 1/t against the variable.
• Control everything else: volume, total mass and temperature where not being tested.

• Independent variable — the one you deliberately change.
• Fair test — only one variable changes at a time.