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
- Fill a 1 L beaker with at least 800 mL of tap water.
- Place the 1 L beaker directly to the right of the hot plate.
- Attach a universal clamp to the upper part of the stand above the center of the 1 L beaker, in order to support the gas burette.
- Fill the 250 mL beaker with tap water.
- Fill the gas burette to the brim with water from the 250 mL beaker.
- Put a rubber stopper on the gas burette.
- Secure the inverted gas burette to the clamp, so that the opening (end with the rubber stopper) is near the bottom of the 1 L beaker.
- Remove the rubber stopper (the burette must be immersed in the beaker).
If water flows from the burette, it is because there is not enough water in the beaker or the burette is too high. If this is the case, restart steps 4 to 8.
- Place the blue plastic connector so that its J-shaped opening is below the opening of the gas burette.
Measurement of the reaction
- Place the Erlenmeyer flask on the hot plate. Do not turn on the heating element.
- Insert the magnetic stir bar into the Erlenmeyer flask.
- Pour 150 mL of 0.3 M hydrochloric acid (HCl) into the Erlenmeyer flask.
- Using the spatula, take a small quantity of magnesium (Mg) powder and place it in the weighing boat in order to measure a quantity of approximately 0.2 g.
- Deposit the powdered magnesium into the Erlenmeyer flask containing the hydrochloric acid solution.
- 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.
- Start the stopwatch.
- Start the magnetic stirrer.
- Take a reading of the gas volume in the burette every 10 seconds up to 2 minutes.
The results are also available in graphical form in the Results tab. / Volume vs. Time
- After 2 minutes, stop the stopwatch and the magnetic stirrer.
- Remove the stopper from the Erlenmeyer flask and remove the magnetic stirrer.
- Remove the blue plastic connector from the burette.
- Empty the contents of the Erlenmeyer flask into the recovery beaker and rinse it with distilled water.
- Reset the stopwatch.
- Restart steps 4 to 20 with the 0.2 M hydrochloric acid solution.
- Restart steps 4 to 20 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 120 to 180 seconds.
- The reaction will be completed faster with the 0.5M solution, then 0.3M, and finally slower with 0.2M solution.
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)