This laboratory session is designed as a comprehensive exploration of chemical reactions and thermal exchanges through four distinct experiments, each aimed at understanding different aspects of thermochemistry and chemical kinetics.
Educational Goals
- Volume and Temperature Measurement Techniques: Students will refine their skills in using graduated cylinders for volume measurements and thermometers for temperature observations, enhancing their precision and accuracy in experimental chemistry.
- Observation of Chemical Reactions: Participants will gain insights into the nature of chemical reactions, specifically how the mixing of different substances can lead to thermal changes, illustrating the principles of thermochemistry.
- Exploration of Reaction Variations: By altering components such as solvents or reactants, students will explore how experimental conditions affect reaction outcomes, fostering a deeper understanding of chemical kinetics.
- Thermochemistry and Kinetics Concepts: This laboratory aims to provide a practical understanding of thermochemistry and chemical kinetics, emphasizing the thermal effects of chemical reactions and the factors influencing reaction rates.
Through these experiences, students will not only become familiar with standard experimental procedures in chemistry but also gain practical experience in manipulating laboratory equipment and interpreting experimental data.
This hands-on approach to learning allows students to apply theoretical knowledge of chemistry to real-world scenarios, reinforcing their comprehension of fundamental principles within the discipline. The laboratory session highlights the importance of precise measurement and control in chemical experimentation, offering valuable lessons in the thermal behavior of chemical reactions and the impact of varying experimental conditions.
Protocol
Experiment 1: Water + Alcohol
1. Measure 200 mL of water using the graduated cylinder.
2. Pour the water from the graduated cylinder into the calorimeter.
3. Record the initial temperature of the water.
4. Measure 200 mL of ethanol using the graduated cylinder.
5. Pour the ethanol into the calorimeter and then place the calorimeter lid on top.
6. Activate the agitator of calorimeter.
7. Carefully observe the temperature change and note the maximum (or minimum) temperature reached.
8. Empty the calorimeter into the sink and rinse it with room temperature distilled water.
9. Rinse the graduated cylinder with distilled water.
Experiment 2: Water + CaCO3
10. Measure 100.0 mL of water using the 100 mL graduated cylinder.
11. Pour the water from the graduated cylinder into the calorimeter.
12. Record the initial temperature of the water.
13. Weigh approximately 20g of CaCO3(s) using the weighing boat.
14. Pour the CaCO3 into the calorimeter.
15. Attach the calorimeter lid.
16. Activate the stirrer button on the calorimeter lid.
17. Carefully observe the temperature change and note the maximum (or minimum) temperature reached.
18. Empty the calorimeter into the waste beaker and rinse it with room temperature distilled water.
Experiment 3: Water + NH4Cl
19. Repeat Experiment 2, substituting CaCO3 with 10g of ammonium chloride (NH4Cl).
20. Rinse the graduated cylinder with distilled water.
Experiment 4: HCl + NaOH
21. Measure 50.0 mL of 0.5M sodium hydroxide (NaOH) using the graduated cylinder and pour it into the calorimeter.
22. Rinse the graduated cylinder with distilled water.
23. Take the initial temperature of the solution by immersing the digital thermometer in it. The results are in the table.
24. Measure 50.0 mL of 0.5M hydrochloric acid using the graduated cylinder and pour it into the calorimeter.
25. Attach the lid of the calorimeter to the calorimeter.
26. Activate the stirrer button on the calorimeter lid.
27. After a few seconds, note the temperature difference between that recorded by the thermometer (displayed in the table) and that recorded by the calorimeter’s thermometer.
Anticipated Outcomes
Experiment 1:
Water + Ethanol: Expect an exothermic reaction. The temperature should increase, ideally by about 18-20°C, indicating energy release. When ethanol (C2H5OH) is mixed with water (H2O), the two liquids form a solution. This process involves the breaking and forming of intermolecular forces. Initially, the hydrogen bonds between water molecules and the van der Waals forces between ethanol molecules are broken. New hydrogen bonds form between the water and ethanol molecules. The formation of these new intermolecular forces releases energy, resulting in an exothermic reaction that increases the temperature of the solution. The specific heat capacities of the substances and the total energy released during the formation of the new bonds contribute to the observed temperature change.
Experiment 2:
Water + CaCO3: Since CaCO3 is insoluble in water, no significant temperature change is expected, indicating no reaction.
Experiment 3:
HCl + CaCO3: This should result in a reaction where CaCO3 reacts with HCl to produce calcium chloride, water, and carbon dioxide, leading to a temperature increase of about 5 to 8 °C. This experiment involves an acid-base reaction where hydrochloric acid (HCl) reacts with calcium carbonate (CaCO3) to form calcium chloride (CaCl2), water (H2O), and carbon dioxide (CO2). This is a typical acid-carbonate reaction, which is usually exothermic. The breaking of the CaCO3 lattice and the formation of new products releases energy, which may result in a temperature increase in the solution.
Experiment 4:
HCl + NaOH: An exothermic neutralization reaction is expected. The temperature should rise, ideally by about 5-7 °C, indicating the release of energy. This experiment features a neutralization reaction, a type of exothermic reaction where an acid (HCl) and a base (NaOH) react to form water (H2O) and a salt (NaCl). During the reaction, the hydrogen ions (H+) from the acid react with the hydroxide ions (OH−) from the base to form water. This reaction releases energy, increasing the temperature of the mixture. In each experiment, the observed temperature changes are indicators of the energy dynamics involved in the chemical processes, reflecting the exothermic or endothermic nature of the reactions.
Summary of Assignment by Grade Range
1.1.1 Summary of Assignment by Grade Range
Grades 3-5 (Ages 8-10)
- Focus: Basic introduction to chemical reactions, temperature changes, and measurement techniques.
- Activities: Observing simple thermal changes during chemical reactions, using thermometers and graduated cylinders, basic safety instructions.
Grades 6-8 (Ages 11-13)
- Focus: Intermediate understanding of thermochemistry, chemical kinetics, and measurement accuracy.
- Activities: Conducting reactions, measuring volumes and temperatures, observing how different reactants and solvents affect reaction outcomes, following detailed safety protocols.
Grades 9-12 (Ages 14-18)
- Focus: Advanced understanding of thermochemistry, Hess’s Law, and experimental precision.
- Activities: Accurately measuring volumes and temperatures, conducting detailed experiments to explore the thermal effects of chemical reactions, analyzing how changes in reactants and solvents influence reaction rates, detailed recording and interpretation of results, adhering to advanced safety protocols, reinforcing concepts of chemical kinetics and thermodynamics.
Laboratory essentials
Instruments
Beaker (500ml & 1000ml)
Calorimeter
Electronic Scale
Graduated Cylinders (70ml & 250ml)
Spatulas
Thermometers
Timer
Tweezers
Products
Calcium carbonate
Ethanol.
HCl 0.3M (solution).
HCl 0.5M (solution).
Sodium hydroxide 0.5M.