This experimental protocol is designed to measure the volumetric thermal expansion coefficient of a liquid by observing changes in the height of an oil drop within a capillary tube as temperature varies. The experiment starts with setting up the apparatus, including securing the universal clamps, preheating the capillary tube, and preparing beakers with cold water and ice.
Measurements of the oil drop’s height are taken at various temperatures, using a thermometer and a stopwatch, while carefully adjusting the water temperature on the heating plate.
Educational Goals
- Understanding volumetric expansion: Participants will explore how the volume of a liquid changes with temperature, aiming to determine the liquid’s volumetric thermal expansion coefficient.
- Temperature measurement techniques: The experiment introduces methods for accurately measuring temperature and the height of a liquid in a capillary tube, enhancing participants’ familiarity with temperature-related measurements.
- Laboratory instrument manipulation: Students will practice using various laboratory instruments, improving their hands-on skills in conducting experiments.
- Fundamentals of liquid thermodynamics: Through this procedure, participants will gain insights into the basic principles of thermodynamics as they apply to liquids, including the relationship between temperature and volume.
This laboratory experience is crucial for understanding how temperature affects a liquid’s volume and for mastering precise measurement techniques in a laboratory setting.
Participants will develop practical skills in handling laboratory equipment, observing physical phenomena, and analyzing experimental data. Furthermore, this experiment underscores the significance of methodological rigor and accuracy in scientific experimentation, ensuring reliable and meaningful results. Through engaging in this activity, participants not only learn about the thermodynamics of liquids but also appreciate the meticulous nature required in scientific research, enhancing their overall competency in experimental physics and chemistry.
Protocol
PART A: The preparation of the capillary tube
- Above the heating plate; attach a universal clamp to each of the two supports.
- Using the dropper; take some olive oil and place two drops of oil on the watch glass.
- Light the Bunsen burner.
- Using thermal gloves; heat the capillary tube along its entire length by exposing it to the flame while making back-and-forth movements for about 20 sec.
- Place the open end (the transparent end) of the very hot tube onto the oil drops prepared in step 1. The oil should rise on its own into the capillary tube.
- Return the tube to an upright position (open end facing upwards) and wait a few seconds for it to cool.
- Attach the capillary tube to the universal clamp of the right support; positioning the open (transparent) end upwards.
- Turn off the Bunsen burner.
- The drop of oil in the capillary tube should have a thickness between 5 mm and 1 cm.
PART B: Measurement of the volume-temperature relationship
- Place the 250 mL beaker on the hot plate (do not turn on the hot plate).
- Place the magnetic stirrer in the beaker.
- Attach the thermometer to the universal clamp of the left stand and place it vertically in the 250 mL beaker. Neither the capillary tube nor the thermometer should touch the walls of the beaker.
- Secure the ruler behind the capillary tube to measure the height of the oil drop.
- Take the beaker containing ice and add 250 ml of cold tap water to it.
- Then pour the cold water and ice into the beaker containing the capillary tube. The water level must exceed that of the oil drop.
- Observe the water temperature and the height of the bottom of the oil drop once the temperature has stabilized.
- Start the stirrer on the hot plate.
- Start the stopwatch.
- Turn on the heating plate at low intensity (20°C) and wait for the temperature to rise by about ten degrees.
- In the results table; observe the water temperature and the height of the bottom of the oil drop once the temperature has stabilized. You will notice the change in the height of the drop based on changes in the water temperature.
- Repeat steps 18 and 19 while increasing the temperature of the plate by an additional 10 degrees.
- Turn off the hot plate and wait for everything to cool down.
- Note: The inside of the capillary tube has a radius of 0.5 mm.
Anticipated Outcomes
Participants explore the ideal gas law, which states that the volume of a gas is directly proportional to its temperature when pressure and the amount of gas are held constant. This experiment provides a visual and quantitative understanding of how gas volume changes in response to temperature variations.
- Temperature-volume relationship: As the temperature of the gas (in this case, air within the capillary tube) increases, the volume, indicated by the height of the oil drop, is expected to increase. Conversely, when the temperature decreases, the volume should decrease. The inside of the capillary tube has a radius of 0.5 mm.
- The relation follows the ideal gas law, where pV=nRT, where p= pressure (Pa), V=Volume (/1000L), n = moles, R = 8.314 J/mol*K, and T is the temperature in kelvins.
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The results should be approximately:
Temperature
(°C)
Absolute temperature
(K)
Height
(mm)
Air volume
(mL)
4,0
277,2
47,3
0.037
11,5
284,7
48,6
0.038
20,5
293,7
50,0
0.039
29,0
302,2
51,5
0.04
41,5
314,7
53,7
0.042
50,0
323,2
55,1
0.043
62,0
335,2
57,2
0.045
72,5
345,7
59,0
0.046
80,5
353,7
60,3
0.047
91,0
364,2
62,1
0.049
-
The volume (V, in mL) of a gas (at constant moles and pressures) will follow the relation V = π*r2*h, where r=cylinder radius (0.05cm) and observed height (in cm). The plot will be a constant linear increase of Volume vs. Temperature.
- Data collection and analysis: By systematically recording the temperature and corresponding oil drop height at various temperatures, participants will create a dataset that, when graphed, should show a linear relationship between temperature (in Kelvin) and volume, affirming the ideal gas law.
- Observation skills: Participants will refine their observation skills, noting how minute changes in temperature can result in measurable changes in the volume of gas.
Significance and Lessons Learned:
- Understanding gas behavior: The experiment deepens the understanding of fundamental gas laws, specifically the ideal gas law, showing how gases expand when heated and contract when cooled in a controlled environment.
- Real-world relevance: The principles demonstrated are applicable in various real-world scenarios, such as understanding the behavior of air in weather balloons, automotive engines, and even in meteorology for weather prediction.
- Scientific methodology: Participants learn the importance of precise measurements and the need to control variables to isolate the effects of temperature on gas volume. This reinforces the scientific method’s role in experimental design and data analysis.
- Critical thinking: Analyzing the results, participants will engage in critical thinking, especially if the outcomes deviate from the expected linear relationship, prompting investigation into possible sources of error or non-ideal gas behavior.
- Practical skills: Handling laboratory equipment like Bunsen burners, capillary tubes, and thermal gloves develop practical skills and reinforces the importance of laboratory safety protocols.
This experiment offers a comprehensive learning experience, merging theoretical knowledge with practical skills, enhancing participants’ understanding of gas laws and their competence in conducting scientific investigations.
Summary of Assignment by Grade Range
Grades 3-5 (Ages 8-10)
- Focus: Basic introduction to temperature and volume concepts.
- Activities: Observing simple demonstrations of how temperature affects the volume of liquids, basic safety instructions.
Grades 6-8 (Ages 11-13)
- Focus: Intermediate understanding of volumetric expansion and temperature measurement.
- Activities: Measuring temperature and liquid height in a capillary tube, recording changes in volume with temperature, following detailed safety protocols.
Grades 9-12 (Ages 14-18)
- Focus: Advanced understanding of volumetric expansion, precise measurement techniques, and thermodynamics principles.
- Activities: Setting up and using the apparatus to measure the volumetric thermal expansion coefficient, accurately measuring temperature and liquid height, analyzing the relationship between temperature and volume, detailed recording and interpretation of results, adhering to advanced safety protocols, reinforcing concepts of liquid thermodynamics.
Laboratory essentials
Instruments
- Beaker (250ml)
- Bunsen burner
- Capillary tube
- Dropper
- Hot plate
- Lab Stand & Clamps
- Magnetic stirrer
- Ruler
- Thermometers
- Timer
- Watch glass
Products
- Olive oil