063 – The influence of concentration on reaction rate 1

This laboratory session is designed to quantify the volume of gas produced from the reaction between powdered magnesium and hydrochloric acid at varying concentrations. Through this procedure, students will delve into the principles of chemical stoichiometry, reaction kinetics, and the influence of reactant concentration on reaction speed.

Educational Goals

  • Stoichiometry and Gas Production: Students will explore the stoichiometric relationships between solid reactants and gaseous products in chemical reactions, enhancing their understanding of mass-to-gas conversions.
  • Chemical Kinetics Exploration: The experiment allows observation of how varying concentrations of hydrochloric acid influence the rate of gas production, providing a practical example of reaction kinetics.
  • Experimental Technique Development: Participants will refine their skills in using laboratory equipment for measuring gas volumes, improving their experimental methodology.
  • Data Interpretation Skills: Students will learn to analyze experimental results to derive insights into chemical kinetics laws, fostering their ability to understand and apply chemical principles.

By engaging in this laboratory, students gain practical insights into the impact of reagent concentration on the speed of chemical reactions. They learn to accurately measure gas production during a reaction and analyze how different variables affect this process. Experience reinforces the importance of precise experimental practices and data analysis in understanding fundamental chemistry principles, equipping students with the skills necessary for conducting experimental research.

Protocol

Assembly of the gas burette

  1. Fill a 1 L beaker with at least 800 mL of tap water.
  2. Place the 1L beaker to the right of the stand.
  3. Place a universal clamp above the center of the 1L beaker, to support the gas burette.
  4. Fill the 250 mL beaker with tap water.
  5. Fill the gas burette with water from the 250mL beaker; then place a rubber stopper in it.
  6. Place the inverted gas burette in the clamp so that the opening is near the bottom of the 1L beaker.
  7. Remove the rubber stopper (the burette must be immersed in the beaker).
  8. If water flows out of the burette, it means there is not enough water in the beaker or the burette is too high. Repeat steps 4 to 7.
  9. Place a plastic connector so that its J-shaped opening is under the opening of the gas burette.

Measurement of the reaction

  1. Place the Erlenmeyer flask on the heating plate. Do not turn on the heating element.
  2. Insert the magnetic stirrer into the Erlenmeyer flask.
  3. Pour 150 mL of 0.3 M hydrochloric acid (HCl) into the Erlenmeyer flask.
  4. Using the spatula, take a small amount of magnesium (Mg) powder and place it in the weighing boat to measure an amount of about 0.2 g.
  5. Place the powdered magnesium in the Erlenmeyer flask containing the hydrochloric acid solution.
  6. Place the two-hole stopper; coupled to the glass elbow; on the Erlenmeyer flask.

Ensure that the glass elbow on the Erlenmeyer flask is aligned (connected) to the plastic connector attached to the gas burette.

  1. Start the stopwatch.
  2. Start the magnetic stirrer.
  3. Take a reading of the volume every second for 2 minutes.
  4. Stop the stopwatch and the magnetic stirrer.
  5. Open the Erlenmeyer flask; retrieve the magnetic stirrer; empty it into the recovery beaker and rinse it with distilled water.
  6. Repeat steps 4 to 21 with the 0.2 M hydrochloric acid solution.
  7. Repeat steps 4 to 21 with the 0.5 M hydrochloric acid solution.

Note that the reaction is accelerated 10x.

Anticipated Outcomes

  • 0.2076g of Mg(s) is 0.085 moles, which will produce 0.085 moles of H2.
  • 0.085 moles of H2 will occupy a volume approx. 204 mL.
  • The reaction will be completed in about 60 seconds.

Summary of Assignment by Grade Range

Grades 3-5 (Ages 8-10)

  • Focus: Basic introduction to reaction rates and gas production concepts.
  • Activities: Observing gas production from reactions of powdered magnesium with different concentrations of hydrochloric acid, simple discussions on how concentration affects reaction speed, basic safety instructions.

Grades 6-8 (Ages 11-13)

  • Focus: Intermediate understanding of stoichiometry, reaction kinetics, and gas production.
  • Activities: Conducting reactions with powdered magnesium and varying concentrations of hydrochloric acid, measuring the volume of gas produced, observing how concentration affects reaction rate, following detailed safety protocols.

Grades 9-12 (Ages 14-18)

  • Focus: Advanced understanding of stoichiometry, reaction kinetics, and data interpretation.
  • Activities: Accurately conducting reactions with powdered magnesium and different concentrations of hydrochloric acid, measuring and recording the volume of gas produced, analyzing the impact of reactant concentration on reaction rate, detailed recording and interpretation of results, adhering to advanced safety protocols, reinforcing concepts of chemical kinetics and stoichiometry.

Laboratory essentials

Instruments

  • Beaker (500 ml, 1000 ml)
  • Electronic scale
  • Elbow holed cap
  • Erle
  • Gaz burette
  • Graduated cylinders (250 ml)
  • Hot plate
  • Lab Stand & Clamps
  • Magnetic stirrer
  • Plastic connector
  • Spatula
  • Stopper
  • Thermometers
  • Timer

Products

  • HCl 0.2 M (solution)
  • HCl 0.3 M (solution)
  • HCl 0.5 M (solution)
  • Magnesium (powder)
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