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 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.
Protocol
Magnesium
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 0.4g.
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 230 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.
Magnesium Oxide
16. Weigh about 0.4 g of magnesium oxide (MgO) powder.
17. Repeat steps 4 to 15 with MgO.
18. Note the difference between the two molecules.
** Note: the reaction is accelerated 2 times faster, to more easily observe the complete reaction.
Anticipated Outcomes
Using approx. 0,41 g of magnesium and 100 mL of 1M HCl, the reaction should take approx. 490 seconds, or 98 seconds accelerated 2 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 7.57 kJ, with a 18 ℃ 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. The molar enthalpy of reaction of MgO is -120kJ for each mole of MgO(s). The energy released should be 2.06 kJ, with a 5 ℃ temperature increase. Using approx. 0,43 g of magnesium oxide and 100 mL of 1M HCl, the reaction should take approx. 10-15 seconds less than Mg(s), when accelerated 2 times.
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 0.1M (solution)
Magnesium (powder)
Magnesium oxide (powder).