Rate of Reaction Practical Gas
Reaction: magnesium + hydrochloric acid → magnesium chloride + hydrogen
Aim: To investigate how a factor (concentration, temperature, surface area, catalyst) affects the rate of reaction.
Method:
Magnesium ribbon is added to hydrochloric acid in a conical flask connected to a gas syringe. The volume of hydrogen gas produced is measured at regular time intervals, or the time to collect a fixed volume is recorded.
Independent variable: Factor changed (e.g. acid concentration).
Dependent variable: Rate of reaction, measured by volume of gas per second or time taken to produce a set volume.
Control variables: Mass/surface area of magnesium, volume of acid, temperature, same apparatus.
Results: Faster reaction = steeper gradient on a gas volume–time graph.
Reliability & improvements: Repeat and calculate a mean; ensure the system is airtight to prevent gas loss
Rate of Reaction – Disappearing Cross Practical
Aim: To investigate how a factor (usually concentration or temperature) affects the rate of reaction.
Reaction: sodium thiosulfate + hydrochloric acid → sulfur (solid) + sodium chloride + sulfur dioxide + water
Method:
A conical flask containing sodium thiosulfate is placed over a black cross on paper. Hydrochloric acid is added and a stopwatch started. The time taken for the cross to disappear (as sulfur forms) is recorded.
Independent variable: Concentration of sodium thiosulfate (or temperature).
Dependent variable: Rate of reaction, measured by 1 ÷ time taken for the cross to disappear.
Control variables: Volume of solutions, total volume, temperature (if not tested), same observer and lighting conditions.
Results: Shorter time (or larger 1/time value) = faster reaction.
Reliability & improvements: Repeat and calculate a mean; results are subjective — improve by using a light sensor instead of human judgement.
