This protocol is centered on evaluating how the concentration of hydrochloric acid affects its reaction time with powdered magnesium and the resultant temperature changes.
Through this experimental setup, students will have the opportunity to delve into the principles of chemical kinetics, thermodynamics, and stoichiometry.
Educational Goals
- Chemical Kinetics: Gain an understanding of how the concentration of hydrochloric acid influences the speed of its reaction with magnesium, providing insights into reaction rates.
- Thermodynamics: Observe and record the temperature changes during the reaction to identify its exothermic or endothermic nature, enhancing comprehension of energy changes in chemical processes.
- Experimental Skills: Develop precision in measuring liquids and solids and in monitoring chemical reactions, improving experimental technique and accuracy.
- Analysis and Interpretation: Learn to analyze time-based and thermal data to understand the impact of reactant concentration on the reaction, fostering analytical and interpretive skills in chemistry.
By investigating the effect of hydrochloric acid concentration on its reaction with magnesium, this experience offers valuable insights into the dynamics of chemical reactions.
Students will not only observe firsthand the influence of reactant concentration on reaction rate and temperature changes but also apply these observations to understand the interplay between chemical kinetics and thermodynamics. The skills and knowledge acquired through this laboratory are fundamental for designing chemical processes and for a deeper understanding of chemical reactions, preparing students for advanced studies and research in chemistry.
Protocol
Part 1: reaction with 1M HCl
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 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 with 2M HCl
16. Measure 100 mL of 2M hydrochloric acid (HCl).
17. Repeat steps 4 to 15, comparing the two concentrations of HCl.
18. Observe and note the time needed for the reaction to reach completion, as previously indicated by temperature stabilization.
**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 245 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. Using HCl 2M will accelerate the reaction, which should take approx. 330 seconds, or 165 seconds accelerated 2 times.
Summary of Assignment by Grade Range
Grades 3-5 (Ages 8-10)
- Focus: Basic introduction to reaction rates, temperature changes, and concentration effects.
- Activities: Observing reactions of powdered magnesium with hydrochloric acid at different concentrations, noting simple differences in reaction speed and temperature changes, basic safety instructions.
Grades 6-8 (Ages 11-13)
- Focus: Intermediate understanding of reaction kinetics, thermodynamics, and concentration effects.
- Activities: Conducting reactions with powdered magnesium and varying concentrations of hydrochloric acid, measuring temperature changes, observing how concentration affects reaction rate and temperature, following detailed safety protocols.
Grades 9-12 (Ages 14-18)
- Focus: Advanced understanding of chemical kinetics, thermodynamics, and data analysis.
- Activities: Accurately conducting reactions with powdered magnesium and different concentrations of hydrochloric acid, measuring and recording temperature changes and reaction times, analyzing the impact of reactant concentration on reaction rate and thermal changes, detailed recording and interpretation of results, adhering to advanced safety protocols, reinforcing concepts of chemical kinetics, thermodynamics, and stoichiometry.
Laboratory essentials
Instruments
Beaker (1000ml)
Calorimeter
Electronic Scale
Graduated Cylinders (70ml & 250ml)
Spatulas
Thermometers
Timer
Tweezers
Products
HCl 2.0M (solution)
HCl 1.0M (solution)
Magnesium (powder)