This experiment is structured to identify unknown substances by measuring key physical properties: boiling points for liquids and density for solids. It’s split into two parts for a comprehensive approach.
Part A: targets the identification of unknown liquids. It involves precise volume measurements, controlled heating to 105°C, and monitoring boiling behavior to ascertain each liquid’s boiling point. This step is critical for identifying the liquids or comparing them to known substances. Part B: focuses on the identification of unknown solids through density measurements. This includes weighing the solids, using water displacement to measure volume—a technique inspired by Archimedes’ principle—and calculating density by dividing mass by volume. This process is pivotal for distinguishing or identifying solid substances
Educational Goals
- Mastering measurement techniques: Enhance skills in accurately measuring volume and mass, foundational for scientific analysis.
- Understanding physical properties: Deepen knowledge of how boiling points and density serve as identifiers for substances.
- Applying theoretical principles: Apply principles of physics and chemistry, like Archimedes’ principle, to real-world scenarios.
- Developing analytical skills: Cultivate the ability to analyze and identify substances based on their physical properties, utilizing comparisons to known materials for verification or identification.
- Integrating disciplinary knowledge: Demonstrate the integration of chemistry and physics through practical applications, underscoring the interdisciplinary nature of scientific inquiry.
By engaging in this experiment, participants will not only apply essential laboratory techniques but also learn to distinguish and characterize chemicals through their physical properties. This hands-on experience with H2O, ethanol, CaCO3, and Fe(OH)3 as test substances underscores the practical use of boiling point and density in substance identification, offering a profound understanding of the principles guiding the identification of unknown substances in scientific exploration.
Protocol
1. Accurately measure 50 mL of unknown liquid #1 using the 50 mL graduated cylinder.
2. Pour the liquid into a 100 mL beaker labeled A”.
3. Rinse the graduated cylinder.
4. Repeat steps 1 to 3 with unknown liquid #2, using beaker B.
5. Place both beakers on 2 heating plates.
6. Place a magnetic stir inside each beaker.
7. Insert a thermometer into each beaker in such a way that the tip does not touch the bottom, using a universal stand and clamps.
8. Start the stopwatch.
9. Turn on the magnetic stirrers.
10. Adjust the temperature of the heating plates to 105°C.
11. Check the temperature changes in the results table.
12. Based on the boiling point, what could the unknown liquids be?
Identification of unknown solids
1. Weigh 5 pieces of unknown solid #1 on the scale.
2. Fill the overflow jar with water and let the water drain into the sink.
3. Place a 25 mL graduated cylinder under the spout of the overflow jar.
4. Gently immerse solid #1 into the overflow jar. Be careful! Do not let your fingers touch the water to avoid affecting the results.
5. Collect the overflow water in the 25 mL graduated cylinder.
6. Wait for the water flow to stop completely.
7. Record the weight of the pieces, as well as the volume occupied. This will allow you to calculate the density.
8. Remove solid #1 from the overflow jar.
9. Fill the overflow jar with water and let the water drain into the sink.
10. Place a 25 mL graduated cylinder under the spout of the overflow jar.
11. Weigh a piece of unknown solid #2 on the scale.
12. Gently immerse solid #2 into the overflow jar. Be careful! Do not let your fingers touch the water to avoid affecting the results.
13. Collect the overflow water in the 25 mL graduated cylinder.
14. Record the weight of the pieces, as well as the volume occupied. This will allow you to calculate the density.
15. Thus, you will be able to identify the 2 unknown solids using their density.
Anticipated Outcomes
Unknown Liquid #1 is water
Unknown Liquid #2 is ethanol. Since the boiling point of ethanol is 78°C, it will boil faster than water, which has a boiling point of 100°C.
Unknown Solid #1 is calcium carbonate (CaCO3), where one-piece weighs 2.9 grams and five pieces weigh 14.5 grams. With a density of 2.71 g/mL, these five pieces will occupy a volume of 5.4 mL
Unknown Solid #2 is iron (III) hydroxide (Fe(OH)3), with one piece weighing 12.75 grams and five pieces weighing 63.75 grams. Given its density of 4.25 g/mL, the total volume occupied by these pieces will be 15 mL
Liquid Identification: By heating two unknown liquids to 105°C and observing their boiling points, students deduce that Liquid #1 (water) boils at 100°C and Liquid #2 (ethanol) at 78°C. This experiment not only demonstrates the concept of boiling points but also introduces a method to identify substances based on their physical properties.
Solid Identification: Through displacement method, participants determine the density of two unknown solids. They discovered that Solid #1 (calcium carbonate, CaCO3) has a density of 2.71 g/mL and occupies a volume of 5.4 mL, and Solid #2 (iron (III) hydroxide, Fe(OH)3) has a density of 4.25 g/mL, occupying a volume of 15 mL. This part of the lab reinforces the concept of density and its role in identifying substances.
Safety and Precision: The importance of safety in the lab is highlighted through the use of protective gear and proper handling of materials. Precision in measurement is crucial for accurate scientific results.
Understanding Physical Properties: Students learn that physical properties like boiling point and density are key to identifying substances. This hands-on experience reinforces theoretical knowledge.
Scientific Method: The protocol exemplifies the scientific method—making observations, forming hypotheses, conducting experiments, and drawing conclusions. Problem-solving: Students apply critical thinking and problem-solving skills to deduce the identity of unknown substances, an essential skill in scientific inquiry.
Summary of Assignment by Grade Range
Grades 3-5 (Ages 8-10)
- Focus: Basic introduction to boiling points and density, simple measurements.
- Activities: Observing boiling points, measuring volume and mass, basic calculations, basic safety instructions.
Grades 6-8 (Ages 11-13)
- Focus: Intermediate understanding and application of measurement techniques and physical properties.
- Activities: Measuring volume and mass, observing boiling points, applying Archimedes’ principle, recording observations, following detailed safety protocols.
Grades 9-12 (Ages 14-18)
Focus: Advanced mastery of measurement techniques and analytical skills.
Activities: Detailed measurement of physical properties, precise control of experimental conditions, advanced calculations, applying theoretical principles, detailed recording and analysis, adhering to advanced safety protocols.
Laboratory essentials
Instruments
Beakers (100ml & 1000ml)
Droppers
Electronic Scale
Graduated Cylinders (25ml & 50ml)
Hot plate
Lab Stand & Clamps
Magnetic stirrer
Overflow Vessel
Spatulas
Thermometers & Timer
Tweezers
Products
Unknown liquids (#1 & #2).
Unknown solids (#1 & #2).