The law of conservation of mass is a fundamental principle in chemistry, first articulated by Antoine Laurent de Lavoisier in the 18th century. It states, “Nothing is lost, nothing is created, everything is transformed.” This principle is verified through chemical reactions by demonstrating that the total mass of reactants equals the total mass of products, provided the system is closed. In this experiment, two chemical reactions will be conducted to validate the conservation of mass.
Educational Goals
- Understand chemical reactions: Gain detailed insights into various types of chemical reactions, including gas evolution and precipitate formation, and their role in confirming conservation laws.
- Explore experimental integrity: Investigate the importance of maintaining a closed system for accurate experimental validation of mass conservation principles.
- Enhance laboratory techniques: Develop proficiency in using scientific tools like balances, graduated cylinders, and reaction vessels to achieve accurate measurements and reliable results.
- Encourage curiosity: Foster curiosity through experimentation with alternative reactants and conditions, promoting a deeper understanding of chemical processes.
- Critical data analysis: Learn to analyze data critically, identify sources of experimental error, and propose strategies to mitigate these errors for future experiments.
- Link theory and practice: Bridge theoretical principles of conservation laws with hands-on laboratory experiences to solidify understanding and applicability in real-world contexts.
Protocol
Part A: The reaction between sodium bicarbonate and acetic acid
- Weigh the rubber balloon using the scale.
- Using the weighing basket, weigh approximately 2 g of sodium bicarbonate (NaHCO3).
- Introduce the weighed powder into the rubber balloon.
- Measure 25 ml of acetic acid (CH3COOH) with the graduated cylinder and pour it into the Erlenmeyer flask.
- Attach the clip to the base of the balloon.
- Attach the balloon to the opening of the Erlenmeyer flask, taking care not to drop the solid into the liquid.
- Weigh the system (flask, clamp, Erlenmeyer flask, and the two reactants) before the reaction. Record the mass in the results table.
- Detach the clip from the balloon.
- By pressing the glass rod on the balloon; drop the solid into the Erlenmeyer flask.
- Gently shake the solution until it is completely dissolved by swinging the Erlenmeyer flask from left to right.
- Attach the clip to the base of the balloon.
- Weigh the system again once the reaction is completed. The mass is found in the results table.
- Detach the balloon (keep the clamp at the base) from the Erlenmeyer flask.
- Weigh the balloon with the attached clamp.
Part B: The reaction between calcium dichloride and disodium carbonate
- Measure 15 ml of calcium dichloride (CaCl2) solution with the graduated cylinder.
- Pour the solution into the 50 ml beaker #1.
- Weigh beaker #1 on the balance scale.
- Measure 15 ml of sodium carbonate (Na2CO3) solution with the graduated cylinder.
- Pour the solution into the 50 ml beaker #2.
- Weigh beaker #2 on the balance scale.
- Pour the contents of beaker #1 into beaker #2. Stir with the glass rod.
- Shake the contents of beaker #2 with the glass rod.
- Weigh the two beakers after the reaction and record the mass in the results table.
Optional Extensions
Repeat the reactions using different salts available in the laboratory, such as sodium chloride (NaCl) or potassium sulfate (K₂SO₄). Record any changes in precipitate formation or other observations.
Anticipated Outcomes
- Mass conservation validation: Demonstrate that the total mass of the system remains constant before and after each reaction, confirming the law of conservation of mass.
- Observable reactions:
- Part A: Expect to observe vigorous bubbling as carbon dioxide gas (CO₂) is released during the reaction between sodium bicarbonate and acetic acid.
- Part B: A white precipitate (calcium carbonate, CaCO₃) will form, indicating the chemical reaction between calcium dichloride and disodium carbonate.
- Data consistency: Experimental results should show negligible differences in mass measurements, with slight variations attributed to equipment sensitivity or minor leaks in the system.
- Extended understanding: Replicating the experiments with alternative salts (e.g., NaCl, K₂SO₄) will broaden understanding of reaction behavior and outcomes.
- Skill development: Participants will enhance their ability to conduct precise measurements, observe reaction dynamics, and draw conclusions from empirical data.
- Environmental implications: Encourage reflection on the importance of chemical reactions in environmental processes, such as water treatment and industrial applications.
Summary of Assignment by Grade Range
Grades 9-10
- Focus: Introduce students to the foundational concept of mass conservation in chemistry.
- Activities:
- Record initial and final system masses accurately.
- Observe key reaction indicators like gas evolution and precipitate formation.
- Complete data tables and answer guided questions about the experiments.
- Goals:
- Understand the visible evidence of chemical transformations.
- Develop basic measurement and observation skills.
- Relate the experimental results to theoretical principles of mass conservation.
Grades 11-12
- Focus: Apply and analyze experimental methods to validate conservation laws in a more detailed manner.
- Activities:
- Perform stoichiometric calculations to predict expected masses of reactants and products.
- Investigate experimental discrepancies and propose reasons for any deviations.
- Explore alternative reactants or experimental conditions for further validation.
- Goals:
- Link theoretical knowledge of stoichiometry and reaction types to laboratory practice.
- Strengthen critical thinking skills by analyzing and interpreting experimental data.
- Deepen understanding of the law of conservation of mass and its applications.
College-Level/Advanced Students
- Focus: Conduct an in-depth exploration of reaction mechanisms, system design, and advanced applications of conservation principles.
- Activities:
- Design variations of the experiments to test hypotheses about reaction behavior in different conditions.
- Assess the impact of open vs. closed systems on reaction mass and outcomes.
- Research real-world applications of mass conservation, such as industrial chemical processes and environmental chemistry.
- Goals:
- Refine experimental techniques and evaluate their precision.
- Explore broader scientific implications of conservation laws.
- Enhance the ability to critically analyze and present findings in professional contexts.
Laboratory essentials
Instruments
Triple-beam balance
Weigh-in basket
Rubber balloon
Wood clamp
Spatulas
Glass rod
250mL Erlenmeyer
2x 50mL beakers
25mL graduated cylinder
Products
Sodium bicarbonate (powder)
Acetic acid 1M (solution)
CaCl2 1M (Solution)
Na2CO3 1M (solution)