Educational Goals
- Preparation and Reaction of Chemical Solutions: Participants will learn to accurately prepare solutions of calcium chloride and ammonium oxalate and mix them to initiate a chemical reaction, emphasizing the procedural aspects of chemical experimentation.
- Observation of Mass Changes: The experiment aims to illustrate the concept of mass conservation in chemical reactions by measuring the mass changes before and after the reaction, providing tangible evidence of the reaction’s outcome.
- Understanding Precipitation Reactions: Through the formation of a precipitate from the reaction, participants will explore the principles behind precipitation reactions, including solubility rules and the role of ionic compounds in aqueous solutions.
- Analytical Skills Development: This session is designed to enhance participants’ analytical skills in observing, documenting, and interpreting the results of chemical reactions, fostering a deeper understanding of chemical processes and their quantitative aspects.
By engaging in this laboratory session, participants will gain hands-on experience with the chemical reaction between calcium chloride and ammonium oxalate, from the preparation of solutions through to the observation of the reaction’s effects. This practical exploration will not only demonstrate the principles of precipitation and mass conservation but also provide valuable insights into the meticulous nature of conducting chemical experiments. Through this process, participants will enhance their understanding of key chemistry concepts, reinforcing their knowledge and skills in the discipline.
Protocol
1. Initial weighing of the beaker: Weigh an empty 50 mL beaker and record its mass.
2. Initial weighing of the graduated cylinder: Weigh an empty 10 mL graduated cylinder and record its mass.
3. Measurement of calcium chloride: Using the graduated cylinder, accurately measure 5 mL of calcium chloride solution.
4. Transfer of calcium chloride: Pour the measured calcium chloride solution into the 50 mL beaker.
5. Rinsing of the graduated cylinder: Use a wash bottle to rinse the graduated cylinder with distilled water.
6. Measurement of ammonium oxalate: Accurately measure 5 mL of ammonium oxalate solution with the same graduated cylinder.
7. Weighing of the calcium chloride solution: Weigh the beaker now containing the calcium chloride solution and note the mass.
8. Weighing of the ammonium oxalate solution: Weigh the graduated cylinder containing the ammonium oxalate solution and note the mass.
9. Using the data collected in the previous steps, calculate the mass of the 2 liquids.
10. Combination of solutions: Gently pour the ammonium oxalate solution into the beaker containing the calcium chloride solution.
11. Mixing: Gently mix the solutions for 5 seconds with a glass rod. Note any changes in appearance.
12. Final weighing: Weigh the beaker containing the mixture of the two reactive solutions.
13. Using the data collected in steps 10 to 12, calculate the combined mass of the 2 mixed liquids.
14. Compare the mass of the liquids before and after mixing and note your observations.
Anticipated Outcomes
- The 50mL beaker weighs 100g, and the 10mL graduated cylinder weighs 22.5g.
- 5mL CaCl2 0.2M = 0.111 g + 5g H2O = 5.11g
- 5mL of CaCl2 in the 50mL beaker weighs 105.11g
- 5mL (NH4)2C2O4 = 0.124g + 5g H2O = 5.12g
- 5mL of ammonium oxalate in the 10mL graduated cylinder weighs 27.12g
- 5mL of calcium chloride and 5mL of ammonium oxalate, in the 50mL beaker, weighs 110.23g
- Subtracting the weight of the 50mL beaker, we observe that the weight of mixed solutions is still the same, even if there’s a precipitate on the bottom.
The reaction between calcium chloride (CaCl₂) and ammonium oxalate in an aqueous solution result in the formation of calcium oxalate and ammonium chloride. In this reaction, calcium chloride reacts with ammonium oxalate to produce calcium oxalate, which precipitates out of the solution as a solid, and ammonium chloride, which remains in the aqueous phase. Calcium oxalate is poorly soluble in water, which is why it precipitates out of the solution. This type of reaction is an example of a double displacement reaction, where the cations and anions of the reactants switch places to form new products.
- Conservation of mass: Despite the chemical reaction and the formation of a precipitate (calcium oxalate), the total mass of the system (solutions, beaker, and cylinder) remains constant before and after the reaction, illustrating the law of conservation of mass.
- Formation of precipitate: The visible formation of calcium oxalate as a solid precipitate demonstrates a chemical change, while the total mass remains constant.
Lessons learned:
- Precision in measurement: The experiment emphasizes the importance of precise measurements in scientific experiments, from weighing equipment and substances to measuring liquid volumes.
- Observing chemical changes: Students learn to observe and record physical changes (like the formation of a precipitate) that indicate a chemical reaction has occurred.
- Interpreting results: Understanding the concept of conservation of mass in the context of a chemical reaction, even when the system undergoes visible physical changes.
Chemistry principles:
- Law of conservation of mass: This experiment demonstrates that in a closed system, the mass remains constant regardless of the processes occurring within. The total mass before the chemical reaction is equal to the total mass after the reaction.
- Chemical reactions: The formation of calcium oxalate and ammonium chloride from calcium chloride and ammonium oxalate is an example of a double displacement reaction, a common type of chemical reaction where ions exchange partners.
- Solubility and precipitation: The experiment shows how solubility rules apply in chemical reactions, with calcium oxalate being insoluble in water and forming a precipitate, while ammonium chloride remains dissolved.
By comparing the mass of the reactants and products, students can see firsthand that the mass remains constant, thus reinforcing the principle of mass conservation in a tangible and practical way.
Summary of Assignment by Grade Range
Grades 3-5 (Ages 8-10)
- Focus: Basic introduction to chemical reactions and mass conservation.
- Activities: Observing the mixing of solutions, simple demonstration of mass conservation using scales, basic safety instructions.
Grades 6-8 (Ages 11-13)
- Focus: Intermediate understanding of chemical reactions, stoichiometry, and mass conservation.
- Activities: Preparing solutions of calcium chloride and ammonium oxalate, measuring mass before and after the reaction, observing and recording the formation of a precipitate, following detailed safety protocols.
Grades 9-12 (Ages 14-18)
- Focus: Advanced understanding of stoichiometry, precipitation reactions, and the law of mass conservation.
- Activities: Accurately preparing and mixing solutions, detailed measurement of mass changes before and after the reaction, analyzing the formation and composition of the precipitate, meticulous documentation and interpretation of results, adhering to advanced safety protocols.
Laboratory essentials
Instruments
Beaker (50ml, 100ml, 250ml & 1000ml)
Dropper
Erlenmeyer (25 ml)
Funnel
Gaugeated flask (100ml)
Glass Rod
Graduated Cylinders (10ml & 50ml)
Spatulas
Test tubes
Triple beam scale
Products
Ammonium oxalate (NH4)2C2O4 powder
Calcium chloride powder