This laboratory session is focused on examining how the concentration of acid and the physical form of calcium carbonate (CaCO3) influence reaction rates.
Through experiments using various acids at different concentrations and comparing the reactivity of solid and powdered forms of CaCO3, students will gain insights into chemical kinetics and acid reactivity.
Educational Goals
- Chemical kinetics understanding: Students will explore how the contact surface and concentration of reactants affect reaction speed, demonstrating the fundamental principles of chemical kinetics.
- Acid reactivity comparison: The experiment allows students to observe the varying reactivities between acids like hydrochloric acid and ethanoic acid, emphasizing the impact of acid type on the reaction.
- Chemical principles application: Through the experimental results, students will deepen their understanding of key chemical concepts, including reaction kinetics, solution concentration, and the nature of reactants.
- Practical application skills: The laboratory experience teaches students how to effectively manipulate and control chemical reactions, providing valuable insights applicable in both experimental and industrial settings.
By investigating the effects of acid concentration and the physical state of calcium carbonate on reaction rates, students will enhance their comprehension of the principles that govern chemical reaction speeds. This understanding is crucial for predicting and controlling reactions across various scientific and industrial applications, enriching students’ knowledge, and practical skills in chemistry.
Protocol
Preparation
- Fill the beakers halfway through the following manner:
- Beaker A: hydrochloric acid (HCl) at 2 M.
- Beaker B: ethanoic acid (CH3COOH) at 2M.
- Beaker C: hydrochloric acid (HCl) at 2M.
- Beaker D: hydrochloric acid (HCl) at 1 M.
Experiment 1
- Using the balance, measure exactly 1mL (2.71g) of powdered calcium carbonate using the weighing boat (do not forget to TARE before).
- Place beaker A (2 M hydrochloric acid) on the hot plate.
- Place the magnetic stirrer in the beaker on the hot plate.
- Start the magnetic stirrer using the button on the hot plate.
- Start the stopwatch to measure the duration of the reaction.
- Place the calcium carbonate sample into beaker A.
- Observe the duration of the reaction in beaker A. Stop the stopwatch when the reaction is complete.
- Turn off the magnetic stirrer using the button on the hot plate.
- Remove the magnetic stirrer from the beaker.
- Empty the contents of beaker A into the recovery tank.
- Repeat steps 1 to 10, using beaker B (2M ethanoic acid).
- Compare the results: (beaker A) 2 M hydrochloric acid vs. (beaker B) 2 M ethanoic acid.
Experiment 2
- Weigh a piece of calcium carbonate weighing 2.9g in the weighing boat.
- Place beaker C (2M hydrochloric acid) on the hot plate.
- Place the magnetic stirrer in the beaker on the hot plate.
- Start the magnetic stirrer using the button on the hot plate.
- Start the stopwatch to measure the duration of the reaction.
- Place the calcium carbonate sample in beaker C.
- Observe the duration of the reaction in beaker C. Stop the stopwatch when the reaction is complete.
- Turn off the magnetic stirrer using the button on the hot plate.
- Remove the magnetic stirrer from the beaker.
- Empty the contents of beaker C into the recovery tank.
- Compare the results: (beaker A) 2.71g CaCO3(s) powder vs. (beaker C) 2.9g CaCO3(s) chunks.
Experiment 3
- Using the balance, measure exactly 2.71 g of powdered calcium carbonate using the weighing boat.
- Place beaker D on the hot plate.
- Place the magnetic stirrer in the beaker on the hot plate.
- Start the magnetic stirrer using the button on the hot plate.
- Start the stopwatch to measure the duration of the reaction.
- Place the calcium carbonate sample in beaker D.
- Observe the duration of the reaction in beaker D. Stop the stopwatch when the reaction is complete.
- Turn off the magnetic stirrer using the button on the hot plate.
- Remove the magnetic stirrer from the beaker.
- Empty the contents of beaker D into the recovery tank.
- Compare the results: (beaker A) 2 M hydrochloric acid vs. (beaker D) 1 M hydrochloric acid.
*Note: the reaction is accelerated 10 times faster; to more easily observe the complete reaction
Anticipated Outcomes
Experiment 1:
Reaction time: calcium carbonate (CaCO₃) reacts with 2 M hydrochloric acid (HCl) for approximately 50 seconds, and with 2M ethanoic acid (CH₃COOH) for about 150 seconds.
Observation: HCl reacts faster with CaCO₃ than CH₃COOH due to its stronger acidic nature, which facilitates a quicker release of gas.
It is also possible that the lime water test positive reaction because of the equation CaCO3+CH3COOH→Ca2++CH3COO−+H2O+CO2↑. When the CO₂ from this reaction is bubbled through lime water(a solution of Ca(OH)₂), it causes the lime water to turn milky due to the formation of calcium carbonate precipitate.
Conclusion: the rapid reaction with HCl compared to CH₃COOH illustrates the impact of acid strength on reaction rates.
Experiment 2:
Reaction time: CaCO₃ in powder form reacts in about 50 seconds, whereas in chunks, it takes around 115 seconds.
Observation: the increased surface area of powdered CaCO₃ accelerates the reaction, allowing more acid molecules to interact with the carbonate.
Conclusion: this experiment underscores the significance of surface area in determining the speed of chemical reactions.
Experiment 3:
Reaction time: CaCO₃ reacts with HCl 2M for approximately 50 seconds, and with HCl 1M in about 105 seconds.
Observation: a more concentrated HCl solution yields a faster reaction rate due to the greater availability of H+ ions.
Conclusion: demonstrates how reactant concentration influences the rate of reaction, with higher concentrations facilitating faster reactions.
Lessons learned:
Surface area effect: The reaction rate varies significantly with the surface area of reactants, demonstrating the importance of physical state in chemical kinetics.
Acid strength: The intrinsic strength of an acid determines its reactivity, with stronger acids catalyzing faster reactions.
Concentration’s role: The concentration of reactants is directly proportional to the reaction rate, emphasizing the importance of molecular interactions in chemical processes.
Observational skills: Accurate observation and data recording are crucial for drawing valid conclusions from experimental results.
Rate of reaction: The experiments collectively highlight how various factors like reactant nature, physical state, and concentration govern the speed of chemical reactions.
Acid-base reaction: The interaction between an acid and a base to produce salt, water, and carbon dioxide exemplifies fundamental acid-base reactions.
Collision theory: Aligning with the collision theory, these experiments illustrate that reaction rates are influenced by the frequency and intensity of reactant collisions.
Overall conclusion: the experiments provide valuable practical insights into reaction kinetics, reinforcing the understanding of how different variables influence the rate of chemical reactions.
Summary of Assignment by Grade Range
Grades 3-5 (Ages 8-10)
- Focus: Basic introduction to reaction rates, surface area, and concentration concepts.
- Activities: Observing reactions of solid and powdered calcium carbonate with different acids, noting simple differences in reaction speed, basic safety instructions.
Grades 6-8 (Ages 11-13)
- Focus: Intermediate understanding of surface area effects, concentration effects, and acid reactivity.
- Activities: Conducting reactions with solid and powdered calcium carbonate using different concentrations of hydrochloric acid and ethanoic acid, measuring reaction times, comparing reactivity of different acids and forms of CaCO3, following detailed safety protocols.
Grades 9-12 (Ages 14-18)
- Focus: Advanced understanding of chemical kinetics, surface area effects, and concentration effects on reaction rates.
- Activities: Accurately conducting reactions with various forms of calcium carbonate and acids, measuring and recording reaction times and comparing the impact of different acid concentrations and types, analyzing experimental results to understand the influence of surface area and concentration on reaction rates, detailed recording and interpretation of results, adhering to advanced safety protocols, reinforcing concepts of chemical kinetics and practical application skills.
Laboratory essentials
Instruments
- Beakers (50ml, 100ml, 500ml & 1000ml)
- Electronic Scale
- Graduated Cylinders (70ml & 100ml)
- Hot plate
- Lab Stand & Clamps
- Magnetic stirrer
- Spatulas
- Test Tubes
- Thermometers
- Timer
- Tweezers
Products
- CH3COOH 2 M
- Calcium carbonate (pieces)
- Calcium carbonate (powder)
- HCl 2 M (solution)
- HCl 1 M (solution)