To investigate how changing the concentration of hydrochloric acid influences the rate of a chemical reaction.

Method 1 – Gas Collection:

3. Prepare the Reactants: Clean a strip of magnesium using emery paper.
4. Set Up the Reaction: Place the magnesium strip in a conical flask containing 25 cm³ of a dilute hydrochloric acid solution.
5. Collect the Gas: Quickly seal the flask with a bung connected to a delivery tube and a gas syringe. Start timing as soon as the acid is added.
6. Measure Gas Volume: Record the volume of gas in the syringe every 10 seconds until the volume stops increasing.
7. Final Measurement: Note the time when the gas volume stabilises.
8. Repeat with Different Concentrations: Repeat the experiment with increasing concentrations of hydrochloric acid, increasing by equal increments, until reaching the highest concentration.

Method 2 – Disappearing Cross (Opaque Reaction Mixers):

9. Set Up: Place a white tile with a black cross underneath a clear beaker.
10. Prepare the Reaction Mixture: Add 25 cm³ of sodium thiosulfate solution to the beaker.
11. Start the Reaction: Add 25 cm³ of hydrochloric acid to the beaker and start the timer immediately.
12. Monitor the Cross: Observe the cross from above. Stop the timer when the cross is no longer visible through the cloudy reaction mixture.
13. Record the Time: Note the time taken for the cross to disappear.
14. Repeat with Different Concentrations: Repeat the experiment, increasing the concentration of hydrochloric acid incrementally, until reaching the highest concentration.

Analysis:

• Calculate the Reaction Rate: Use the collected data to determine the rate of reaction for each concentration.

• Graph the Results: Plot the rate of reaction against the concentration of hydrochloric acid and draw a line of best fit.

• Interpret the Graph: A steeper gradient suggests a higher rate of reaction as the concentration of hydrochloric acid increases.