This laboratory session is designed to compare the reactivity and behavior of magnesium in two different forms—powder and ribbon—when reacting with hydrochloric acid (HCl). By measuring the reaction time and temperature changes, students can delve into the concepts of reaction surface area, reaction rate, and activation energy.
Educational Goals
- Surface Area and Reaction Speed: Students will learn how the difference in contact surface area between magnesium powder and ribbon affects the reaction speed, with the powder’s larger surface area typically resulting in a faster reaction.
- Activation Energy: The experiment highlights the role of activation energy in chemical reactions and demonstrates how the physical form of reactants can influence this critical energy threshold.
- Control of Chemical Reactions: Emphasizes the significance of controlling experimental variables to accurately compare the reactivity of different forms of magnesium with HCl.
- Thermodynamics and Kinetics: Through temperature measurements, students will explore thermodynamics and chemical kinetics concepts, observing the heat release and the rate at which reactions occur.
By conducting a comparative analysis of magnesium powder and ribbon reacting with hydrochloric acid, students gain insights into the factors that influence reaction rates. This laboratory underscores the importance of surface area, activation energy, and precise control and measurement in studying chemical reactions, enhancing students’ understanding of fundamental chemistry principles.
Protocol
Part 1: Reaction of magnesium powder with hydrochloric acid
1. Place the weighing boat on the balance scale.
2. Press the tare button to zero out the scale.
3. Weigh the desired amount of magnesium powder (Mg) – about 0.6g.
4. Place the reactant in the calorimeter.
5. Measure the desired amount of 1 M hydrochloric acid (HCl) (100 mL).
6. Note the initial temperature of the HCl.
7. Insert the thermometer into the hole located on the right on top of the lid.
8. Start the stopwatch by pressing the red button.
9. Pour the 1 M HCl into the calorimeter.
10. Place the lid on the calorimeter.
11. Activate the stirrer by pressing the green button on the calorimeter lid.
12. The temperature vs. time graph is on the tablet (graph tab).
13. Note the final temperature when the reaction ends (about 220 seconds).
14. Results can be found in the results tab on the tablet.
15. Empty the contents of the calorimeter into the recycling bin and clean with distilled water.
Part 2: Reaction of magnesium ribbon with hydrochloric acid
16. Weigh about 0.6 g of magnesium ribbon (or an equivalent piece).
17. Repeat steps 4 to 15, compared with the magnesium ribbon.
18. Note the time required until the end of the reaction, determined by the temperature stabilization.
**Note: the reaction is accelerated 10 times faster to more easily observe the complete reaction.
Anticipated Outcomes
Using approx. 0,62 g of magnesium and 100 mL of 1M HCl, the reaction should take approx. 840 seconds, or 84 seconds accelerated 10 times.
The molar enthalpy of reaction, for the reaction Mg(s) + 2 HCl (aq) = MgCl2(aq) + H2(g) is – 440kJ for each mole of Mg(s). The energy released should be about 11.3 kJ, with a 27 ℃ temperature increase. Because Mg(s) is the limiting reagent, using smaller volume will increase time to reach reaction completion, given the smaller amount of HCl participating in the reaction. Using approx. 0,55 g of magnesium ribbons and 100 mL of 1M HCl, the reaction should take approx. 1410 seconds, or 141 seconds accelerated 10 times.
Summary of Assignment by Grade Range
Grades 3-5 (Ages 8-10)
- Focus: Basic introduction to reaction rate and surface area concepts.
- Activities: Observing reactions of magnesium powder and ribbon with hydrochloric acid, noting simple differences in reaction speed, basic safety instructions.
Grades 6-8 (Ages 11-13)
- Focus: Intermediate understanding of surface area effects on reaction rate and basic thermodynamics.
- Activities: Conducting reactions with magnesium powder and ribbon in hydrochloric acid, measuring reaction times and temperature changes, comparing reactivity of different forms of magnesium, following detailed safety protocols.
Grades 9-12 (Ages 14-18)
- Focus: Advanced understanding of reaction kinetics, surface area effects, and thermodynamics.
- Activities: Accurately conducting reactions with magnesium powder and ribbon, measuring and recording reaction times and temperature changes, analyzing the impact of surface area on reaction rate and activation energy, detailed recording and interpretation of results, adhering to advanced safety protocols, reinforcing concepts of chemical kinetics and thermodynamics.
Laboratory essentials
Instruments
Beaker (1000ml)
Calorimeter
Electronic Scale
Graduated Cylinders (70ml & 250ml)
Spatulas
Thermometers
Timer
Tweezers.
Products
HCl 0.1M (solution).
Magnesium (powder).
Magnesium (pieces).