This laboratory session is structured into two distinct parts, with each focusing on different reactions involving magnesium to illustrate the principles of chemical reactions and thermochemistry.
- Part 1: involves reacting powdered magnesium with 1M hydrochloric acid (HCl) in a calorimeter to measure the initial and final temperatures and observe the thermal changes that occur. This part emphasizes the exothermic nature of the reaction between magnesium and hydrochloric acid.
- Part 2: repeats the procedure used in Part 1 but substitutes magnesium with magnesium oxide (MgO) powder to explore the reaction between MgO and hydrochloric acid. This comparison aims to highlight the differences in reactivity and thermal changes between magnesium and its oxide when reacting with hydrochloric acid.
Educational Goals
This laboratory session is designed to help students achieve a set of progressive learning objectives that align with their level of study. Across all age groups, the primary goal is to develop curiosity about chemical processes, reinforce the scientific method, and cultivate safe laboratory practices.
- Conceptual understanding: Students will learn the fundamental principles of chemical reactions, with particular attention to exothermic processes and the relationship between reactants, products, and energy changes. By comparing the reactions of magnesium and magnesium oxide with hydrochloric acid, students will recognize how chemical form and bonding influence reactivity and heat release.
- Practical and technical skills: Learners will develop hands-on laboratory techniques, including accurate measurement of reactants, careful handling of scientific instruments, and systematic observation of temperature changes over time. The activity reinforces the importance of precision, data collection, and reproducibility in experimental science.
- Analytical and critical thinking: Students will analyze differences in thermal energy released by two similar but distinct reactions. They will compare empirical data with theoretical expectations, discuss sources of error, and consider the broader implications of thermochemistry in real-world contexts such as material science and energy applications.
- Scientific communication and safety: Participants will be encouraged to record their findings clearly, interpret results logically, and communicate them effectively in both written and verbal forms. Equally important, they will practice responsible laboratory conduct by adhering to safety protocols and handling chemicals with care.
By the end of the session, students should not only grasp the scientific principles underlying the reactions studied but also gain confidence in applying laboratory skills, evaluating data, and understanding the relevance of thermochemistry to both academic learning and everyday phenomena.
Protocol
- Measure 100 mL of hydrochloric acid (HCl) 1 M using the graduated cylinder.
- Pour the contents of the graduated cylinder into the calorimeter.
- Put the lid on the calorimeter.
- Insert the thermometer into the lid hole.
- Weigh a small piece of magnesium (Mg) ribbon (approximately 0.5 g) using the balance.
- Open the lid and place the piece of magnesium in the calorimeter and close it again as quickly as possible.
- Activate the timer.
- Activate the calorimeter stirrer by pressing the green button on the lid.
- Observe attentively the evolution of the temperature in the results table.
- Wait about 3 minutes or until the temperature no longer increases.
- Stop the stopwatch.
- Reset the timer by pressing the Reset button.
- Stop the agitator by pressing the red button. Remove the thermometer then remove the calorimeter lid.
- Pour the liquid contents of the calorimeter into the black waste container. Remove the piece of magnesium ribbon using the tongs.
- Rinse the calorimeter, the thermometer, and the stirrer with distilled water.
- Let the calorimeter cool for about 30 seconds.
- Repeat steps 1 to 11 with approximately 1 g of magnesium oxide in pieces.
The reaction is accelerated 10 times faster, to more easily observe the complete reaction.
Anticipated Outcomes
- A small chunk of Mg (about 0.55g) will increase the temperature by approximately 22℃ in 140 secs, for 440 kJ per mole of Mg.
- A small chunk of MgO (about 1 g) will increase the temperature by approximately 7℃ in 180 secs, for 120 kJ per mole of MgO.
Summary of Assignment by Grade Range
Grades 3-5 (Ages 8-10)
- Focus: Basic introduction to chemical reactions and temperature changes.
- Activities: Observing temperature changes during reactions, simple comparisons of reactions involving magnesium and magnesium oxide, basic safety instructions.
Grades 6-8 (Ages 11-13)
- Focus: Intermediate understanding of chemical reactions, measurement techniques, and thermochemistry.
- Activities: Conducting reactions with magnesium and hydrochloric acid, measuring temperature changes, comparing reactions with magnesium oxide, understanding heat changes in reactions, following detailed safety protocols.
Grades 9-12 (Ages 14-18)
- Focus: Advanced understanding of thermochemistry, precise measurement techniques, and reaction dynamics.
- Activities: Accurately conducting reactions with magnesium and magnesium oxide in hydrochloric acid, measuring and recording temperature changes, comparing reactivity and heat changes, analyzing experimental conditions and their effects, detailed recording and interpretation of results, adhering to advanced safety protocols, reinforcing concepts of chemical reactions and thermochemistry.
Laboratory essentials
Instruments
- Beaker (1000ml)
- Calorimeter
- Electronic scale
- Graduated cylinders (70ml & 250ml)
- Spatulas
- Thermometers
- Timer
- Tweezers
Products
- HCl 1 M (solution)
- Magnesium (powder)
- Magnesium oxide (powder)