Charles’ Law (Alternate) - Temperature-Volume Relationships for Gases

The objective of this lab is to investigate Charles' Law, which describes the relationship between the volume and temperature of a gas at constant pressure. Students will use tools and equipment for scientific analysis, interpret numerical and graphical data, demonstrate safe practices in the chemical laboratory, demonstrate an understanding of exponential notation and significant figures, demonstrate an understanding of the composition of matter and energy, record their investigation results, use scientific reasoning to evaluate phenomena, and identify unifying themes in the scientific field of study.

The discussion provides an overview of how matter, particularly gases, expands and contracts with changes in temperature. Gases have a greater expansion and contraction range compared to solids and liquids. In this experiment, the focus is on investigating how the temperature of a gas influences its volume when pressure remains constant.

The procedure involves using a glass capillary tube sealed at one end and attaching it to a thermometer using rubber bands. The open end of the tube is positioned close to the thermometer bulb. The tube and thermometer assembly are then immersed into a hot oil bath, ensuring that the entire capillary tube is covered by the oil. The temperature of the oil bath is recorded.

Once the tube and thermometer reach a constant temperature, they are lifted out of the oil bath, allowing some of the oil to rise into the capillary tube. The assembly is then quickly carried to a desk and placed on a paper towel. A reference line is marked at the sealed end of the capillary tube, and the upper end of the oil plug is also marked. The temperature of the air column at this length is recorded.

As the temperature of the gas sample drops, at least six marks are made on the paper towel to represent the length of the air column trapped above the oil plug. The corresponding temperature is written next to each mark. Sufficient time is allowed for the temperature to drop by 60 to 70°C. The length of the air column serves as a relative measure of the gas volume since the tube has a uniform diameter.

When the thermometer shows a steady temperature near room temperature, a final length and temperature observation is made. The steps from 2 to 7 are repeated two more times for a total of three trials. The same capillary tube setup can be used for the additional trials, but different paper towels should be used for measurements.

In the final step, the marked lengths of the gas sample during each trial are measured and recorded in centimeters. It is important to note that the length of the air column trapped in the tube is the distance from the top of the oil plug to the closed end of the tube.

Throughout the lab, students are expected to handle the glass capillary tube and thermometer assembly with care, accurately record temperatures and lengths, and make observations as the gas sample cools. The focus is on understanding the relationship between temperature and volume for gases, applying the principles of Charles' Law, and using length as a relative measure of gas volume.

Objective

·         Use the tools and equipment necessary for basic scientific analysis and research

·         Interpret the numerical and graphical presentation of scientific data

·         Demonstrate safe practices in the Chemical Laboratory

·         Demonstrate an understanding of Charles Law

·         Demonstrate the proper use of Exponential Notation and Significant Figures

·         Demonstrate an understanding of the composition of matter and energy

·         Record the results of investigation through writing

·         Use scientific reasoning to evaluate physical and natural phenomena

·         Identify the unifying themes of the scientific field of study

Materials

·         Glass Capillary Tube

·         Thermometer

·         Small Rubber Bands

·         Hot Oil Bath

·         Paper Towel

Discussion

When matter is heated, it has the ability to expand, whereas it contracts when cooled. It is worth noting that gases exhibit a much larger degree of expansion and contraction compared to solids or liquids.

This experiment focuses on exploring the relationship between the temperature of a gas and its volume when the pressure remains constant. The procedure involves raising the temperature of a slender glass tube containing a confined air sample and subsequently recording the changes in volume as the air sample cools down. Since the tubes possess a consistent diameter, the length of the tube is directly proportional to the volume of the gas contained within. It is important to emphasize that determining the volume of the gas inside the tube is unnecessary; only its length needs to be measured. It is assumed throughout the experiment that the air trapped in the tube and the thermometer are always at the same temperature.

Procedure

1.       Attach a sealed glass capillary tube to the lower end of a thermometer using two provided rubber bands. Secure the open end of the tube closest to the thermometer bulb, positioning it 5-7 mm above the thermometer's end. (Refer to Figure 14)

2.       Submerge both the tube and thermometer into a pre-prepared hot oil bath within a fume hood. Ensure that the entire capillary tube is immersed in the hot oil.

3.       Allow the tube and thermometer to reach the temperature of the oil bath, approximately 120°C. Take note of the oil bath temperature.

4.       Once the tube and thermometer have reached a constant temperature, carefully lift them out of the oil bath, raising about three-quarters of the capillary tube above the oil level. Pause for three seconds to allow some oil to enter the capillary tube. Then, swiftly transport the tube and thermometer back to your workspace, using a paper towel to prevent any dripping.

5.       Place the tube and thermometer on a paper towel on your desk. Create a reference line on the paper at the sealed end of the capillary tube. Additionally, mark the upper end of the oil plug (see Figure 15). Alongside this mark, record the temperature of the air column at this particular length.

6.       As the gas sample's temperature decreases, make a minimum of six marks indicating the length of the air column trapped above the oil plug. Measure this length from the end of the oil plug to the sealed end of the tube. Write the corresponding temperature next to each mark. Allow sufficient time for the temperature to drop by 60 to 70°C. Remember, since the tube has a consistent diameter, the length serves as a relative measure of the gas volume.

7.       Once the thermometer shows a stable temperature, close to room temperature, make a final observation of the length and temperature.

8.       Repeat steps 2-7 two more times. You may reuse the same capillary tube setup for these additional trials. Ensure you use different paper towels for measuring in each trial.

9.       Measure and record the marked lengths of the gas sample for each trial, noting the length of the air column trapped within the tube in centimeters. Remember that this length refers to the distance from the top of the oil plug to the sealed end of the tube.

Report Sheet for CHARLES LAW - TEMPERATURE-VOLUME RELATIONSHIPS FOR GASES

Name_______________________________________                          Date___________________________

Lab / Section_________________________________

Questions for CHARLES LAW (ALTERNATE) - TEMPERATURE-VOLUME RELATIONSHIPS FOR GASES

1.       Prepare a sheet of graph paper for plotting the Volume (Length) and temperature data. The vertical scale should range from 0 to 10 cm; the horizontal scale should include values from -350°C to +150°C.
Label your axes and arrange the scales so the graph fills the entire sheet of graph paper. Plot the temperature Length data for trial #1. Draw the best straight line through the plotted points. Using a dashed line, extend this straight line to the point where it intersects the x-axis. Record the temperature of this point on the graph.

2.       Repeat this procedure for the other two trials. All three trials and intersection temperatures can be shown on the same sheet of graph paper.

Review Questions

1.       What is the objective of this lab?

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2.       Describe the relationship between volume and temperature according to Charles' Law.

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3.       Why is it important to use the proper tools and equipment in scientific analysis and research?

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4.       How can numerical and graphical presentations of scientific data be interpreted?

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5.       Why is it necessary to demonstrate safe practices in the chemical laboratory?

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6.       Explain the concept of matter expanding and contracting with changes in temperature.

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7.       What is the purpose of immersing the capillary tube and thermometer in a hot oil bath?

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8.       What is the significance of marking the reference line and the upper end of the oil plug?

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9.       How does the length of the capillary tube serve as a relative measure of gas volume?

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10.    Why is it important to repeat the experiment multiple times?

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11.    What is the relationship between the temperature of the gas sample and the length of the air column?

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12.    How does the gas sample behave as it cools?

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13.    How would you calculate the volume of the air in the flask at 100°C?

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14.    What factors need to be considered when measuring the length of the marked gas samples?

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15.    How does the experiment demonstrate the principles of Charles' Law?

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16.    What are the potential sources of error in this experiment?

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17.    How would you interpret the data collected during the trials?

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18.    What is the significance of extrapolating the graph to determine the temperature at absolute zero?

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19.    Why is it important to record accurate measurements and observations in scientific investigations?

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20.    How does this lab relate to the broader field of study and the unifying themes in science?

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