Measuring the Rate of a Chemical Reaction

Overview

• Lecturer: Mr. Mitchell from Malmesbury Science
• Focus: Two methods to measure the rate of chemical reaction
• Reaction: Magnesium and Hydrochloric Acid
• Comparison: Two concentrations of Hydrochloric Acid (2 mol/dm³ and 1 mol/dm³)

Procedure

Method 1: Measuring Cylinder

1. Preparation:

   • Use a measuring cylinder to measure 50 cm³ of 2 mol/dm³ HCl.
   • Pour HCl into a conical flask with a bung and delivery tube.
   • Invert a water-filled measuring cylinder; clamp it approx. 1 cm above the trough bottom.

2. Execution:

   • Add magnesium to the conical flask; start the stop clock simultaneously.
   • Ensure the bung is placed immediately to prevent gas escape.
   • Record gas production every 10 seconds.

3. Repeat with 1 mol/dm³ HCl

   • Follow the same procedure to observe a slower reaction rate.

Method 2: Gas Syringe

• Setup similar to Method 1, but measure gas using a gas syringe.
• Note: Keep the gas syringe dry to prevent plunger issues.

Data Collection

• Record the volume of gas produced every 10 seconds.
• Draw a graph with time on the x-axis and volume of gas on the y-axis.
• Observe that the 2-molar HCl shows a steeper curve indicating a faster reaction rate.
• Both reactions reach the same gas volume due to excess HCl, with magnesium as the limiting reactant.

Sources of Error

1. Timing & Coordination:

   • Starting timer, adding magnesium, and sealing flask simultaneously is impractical.
   • Recommended to work with a partner.

2. Gas Loss:

   • Potential hydrogen loss at the start of the reaction.

3. Measurement Precision:

   • Measuring cylinder is imprecise (1 cm³ increments).
   • Suggested use of an inverted burette for precision (0.1 cm³ increments).