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
Identification of unknown liquids
- Precisely measure 50 mL of unknown liquid 1 with the 50 mL graduated cylinder.
- Pour the liquid contained in the graduated cylinder into a 100 mL beaker labeled A.
- Rinse the graduated cylinder.
- Repeat steps 1 to 3 with unknown liquid 2, with beaker B.
- Place beaker A on the left hot plate and beaker B on the right hot plate.
- Place a magnetic stir bar inside each beaker.
- Attach a universal clamp to the stands above the center of each beaker.
- Place a thermometer in each beaker by fastening them to the clamps attached to the universal stands.
- Start the stopwatch.
- Start the magnetic stirrers.
- Adjust the temperature of the hot plates to 105 °C.
- In the results table, check the change in temperature.
- According to the boiling temperature, what could the unknown liquids be?
- When the maximum boiling temperature for each beaker has been reached, stop the magnetic stirrers.
- Stop the stopwatch.
- Lower the temperature of the hot plate to 15°C.
- Detach the thermometers from the clamps.
- Remove the magnetic stir bars from the beakers.
- Empty the contents of the beakers into the recovery bin.
Identification of unknown solids
- Using the tongs, place 5 pieces of unknown solid 1 on the balance using the weighing boat. Record the total weight of the 5 pieces.
- Using tap water, fill an overflow vessel to its full capacity before overflow (500 mL). Let the excess water flow into the sink.
- Place the overflow vessel on the counter right next to the 25 mL graduated cylinder so that the latter is positioned under the overflow opening of the overflow vessel.
- Gently empty the pieces of solid 1 contained in the weighing boat into the overflow vessel. Attention ! Fingers must not come into contact with the water so as not to distort the results.
- Using the overflow from the overflow vessel and the meniscus in the graduated cylinder, determine the volume of solid 1.
- Wait for the flow to stop completely.
- Record the volume occupied. With the weight of the pieces weighed in step 1, you will thus be able to calculate the density.
- Using the tongs, remove the pieces of solid 1 from the overflow vessel and throw them into the recovery bin.
- Empty the liquid contained in the 25 mL cylinder into the recovery bin.
- Using tap water, fill the overflow vessel again to its full capacity before overflow (500 mL). Let the excess water flow into the sink.
- Place the overflow vessel back on the counter right next to the 25 mL graduated cylinder so that the latter is positioned under the overflow opening of the overflow vessel.
- Using the tongs, place 5 pieces of unknown solid 2 on the balance using the weighing boat. Record the total weight of the 5 pieces.
- Gently empty the pieces of solid 2 contained in the weighing boat into the overflow vessel. Attention ! Fingers must not come into contact with the water so as not to distort the results.
- Using the overflow from the overflow vessel and the meniscus in the graduated cylinder, determine the volume of solid 2.
- Record the volume occupied. With the weight of the pieces weighed in step 12, you will thus be able to calculate the density. You will have noted that the liquid becomes dark orange or red after the addition of unknown solid 2.
- You will thus 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).