This educational experience is meticulously structured into two segments, each designed to unravel the fundamental physical properties of paraffin—its density and melting point. These properties are crucial for understanding how paraffin behaves under various conditions and serve as practical illustrations of core principles in chemistry and physics.
Educational Goals
- Comprehension of density: Through the water displacement method, participants will learn how to calculate the density of paraffin, gaining insight into this intrinsic property that is vital for the identification and characterization of materials.
- Understanding of melting Point: The experiment aims to determine the melting point of paraffin, enhancing understanding of the temperature at which a substance transitions from solid to liquid state. This property is essential for substance identification and purity verification.
- Application of theoretical concepts: Engage in practical applications of theoretical concepts such as Archimedes’ principle for volume measurement and the concept of density and melting points, bridging the gap between theory and practice.
- Development of technical skills: Cultivate technical prowess in precise manipulation of measuring instruments and analytical evaluation of experimental data, essential skills for any scientific inquiry.
Part A: Density determination
The objective is to calculate paraffin’s density by first measuring its mass and then determining its volume via water displacement. This process not only illustrates the concept of density but also demonstrates Archimedes’ principle in action.
Part B: Melting point measurement
This segment focuses on identifying the melting point of paraffin by preparing a sample, heating it until it transitions to a liquid state, and monitoring the temperature at which this change occurs. This exercise provides a hands-on understanding of how a substance’s melting point is determined and its significance. This two-part experience offers a comprehensive exploration of the physical properties of paraffin, providing a practical understanding of density and melting point. Through these experiments, participants not only grasp theoretical concepts in a tangible way but also hone their technical skills, from precise measurement to the critical analysis of results. This approach fosters a deeper appreciation for the nuances of material properties and their implications in scientific research and application.
Protocol
Part 1: The density
Place the weighing basket on the scale tray.
2. Press tare to zero the scale.
3. Weigh 5 or 6 pieces of paraffin.
4. Measure the volume of the paraffin sample by water displacement.
a) Measure 20 mL of water with the graduated cylinder.
b) Let the pieces of paraffin slide into the graduated cylinder. Observe the increase in volume.
The final volume, minus the initial volume (20 ml), equals the volume of the paraffin pieces.
5. Verify that the mass and volume of paraffin are correctly recorded in the results table on the tablet.
6. The mass of paraffin divided by its volume is equal to the density of the paraffin (in g/ml).
Part 2: The melting point
7. Fill a 500 mL beaker with cold water (around 6 °C).
8. Place the beaker of cold water on the hot plate.
9. Knowing the density of paraffin, weigh a mass corresponding to a volume of 18 mL to 22 mL. Use the results table on the tablet for assistance.
10. Pour the weighed paraffin into an empty test tube.
11. Using a universal clamp and a universal stand, place the test tube in the beaker of cold water, on the hot plate.
12. Using another universal clamp, place the thermometer in the test tube. The thermometer should not touch the bottom of the test tube, but should be in contact with the paraffin.
13. Start the stopwatch (red button).
14. Set the temperature of the hot plate to 85 °C, wait for all the paraffin to melt and its temperature to start rising again. Follow the progress of the experiment on the chart in the “results” section of the tablet.
15. Turn off the hot plate.
Anticipated Outcomes
The density of paraffin is 0.85 g/mL. 5 or 6 pieces should weigh between 21 and 26 g. The occupied volume should be between 24.7 and 30.6 mL. The melting point of paraffin is around 57 °C. The paraffin will melt and solidify at its melting point, and a plateau of temperature should be observed for a few seconds due to its latent heat of fusion.
The experiment emphasizes the importance of precise measurements, particularly in determining the density and melting point of substances. The careful weighing of paraffin and meticulous volume measurement via water displacement underscore the need for accuracy in scientific experiments.
- Observation and Record-Keeping: Students learn the value of keen observation (e.g., watching paraffin pieces displace water) and diligent record-keeping, essential skills in any scientific endeavor. Recording the mass and volume accurately on the tablet ensures data integrity.
- Understanding Equipment Use: Familiarity with lab equipment, such as balance scales, graduated cylinders, and hot plates, is crucial. This exercise provides hands-on experience, reinforcing the correct usage and importance of each tool in conducting experiments.
- Density Calculation: By dividing the mass of paraffin by its volume, students determine its density, an essential physical property that aids in understanding substance characteristics.
- Melting Point Determination: The experiment allows students to ascertain the melting point of paraffin, a key property that helps categorize and identify substances based on their thermal behavior.
- Conceptual Understanding: Through practical engagement, students gain a deeper understanding of concepts like density and phase changes, solidifying theoretical knowledge through application.
The experiment demonstrates density as a ratio of mass to volume. In this context, paraffin’s density is calculated to understand how compactly its molecules are arranged.
The phase change from solid to liquid is observed as paraffin reaches its melting point. The energy supplied by the hot plate (heat) increases the kinetic energy of paraffin molecules, weakening the forces holding them in a solid structure until they transition to a liquid state.
This method illustrates Archimedes’ principle, where the volume of the displaced water equals the volume of the solid submerged, allowing for the volume measurement of irregularly shaped objects like paraffin pieces. In summary, the experiment is not just a demonstration of measuring physical properties but also an integrated lesson in the practical application of chemistry principles, safety in the lab, and the scientific method.
Summary of Assignment by Grade Range
Grades 3-5 (Ages 8-10)
- Focus: Basic introduction to density and melting point, simple observations.
- Activities: Observing water displacement, watching paraffin melt, basic safety instructions.
Grades 6-8 (Ages 11-13)
- Focus: Intermediate understanding and application of density and melting point concepts.
- Activities: Measuring density, determining melting point, applying basic theoretical concepts, following detailed safety protocols.
Grades 9-12 (Ages 14-18)
Activities: Performing detailed measurements, precise determination of melting points, applying advanced theoretical concepts, adhering to advanced safety protocols.
Focus: Advanced mastery of density and melting point measurements, in-depth analysis.
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
Paraffin (pieces)