Charles' Law
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 Charles' Law, which states that the volume of a gas is directly proportional to its temperature when pressure is held constant. Mathematically, this can be represented as V=kT, where V is the volume, T is the temperature, and k is a constant. The experiment aims to investigate the linear volume-temperature relationship of air by examining the behavior of a gas trapped in a flask as it is subjected to different temperatures.
The lab procedure involves stoppering a dry Erlenmeyer flask with a special rubber stopper assembly. The flask is weighed, and the apparatus is set up with the flask placed in a beaker filled with water. The water is heated to boiling for at least 10 minutes to ensure that the air in the flask reaches the boiling point of water. The pinch clamp is closed, and the flask with its assembly is immersed, inverted, into a sink filled with water at two different temperatures (a low temperature near 0°C and an intermediate temperature near room temperature). As the air in the flask cools, water from the sink is sucked into the flask. The flask is held until the air inside reaches the temperature of the water in the sink. The pinch clamp is then reopened, and the flask is removed from the sink. The volume of water sucked into the flask is determined by weighing the flask after removal.
The calculations in this lab involve determining the weight of water in the flask at the low and intermediate temperatures. This weight is equivalent to the volume of water in the flask at each temperature, assuming the density of water is 1.00 g/mL. The volume of air in the flask at 100°C is obtained by subtracting the weight of the apparatus from the weight of the apparatus when it is full of water. This volume is also equal to the volume of the flask.
Using the obtained measurements and the barometric pressure, the volume of air at the low temperature (V1), volume of air at the intermediate temperature (V2), pressure of air at the low temperature (P1), and pressure of air at the intermediate temperature (P2) are calculated. The volumes of air at the low and intermediate temperatures are then corrected to standard temperature and pressure (STP) conditions (V3 and V4) using the ideal gas law equation (PV = nRT), where P is pressure, V is volume, n is the number of moles, R is the ideal gas constant, and T is the temperature in Kelvin.
A plot of the data is prepared with temperature values ranging from -273 to +100°C on the x-axis and volume in milliliters on the y-axis. The experimental values are plotted, and the best straight line is drawn through the points. The graph is extended until it crosses the x-axis, and the temperature at this point is determined. This extrapolated value represents the temperature of absolute zero.
Throughout the lab, students are expected to follow the procedure carefully, make accurate measurements, perform the necessary calculations, and analyze the data graphically. The focus is on understanding the relationship between volume and temperature for gases, applying the principles of Charles' Law, and determining the temperature at absolute zero through extrapolation.
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
· 250 mL Erlenmeyer Flask
· Glass Tubing
· Rubber Tubing
· Pinch Clamp
· 500 mL Beaker
· Ring Stand
· Bunsen Burner
Discussion
The objective of this experiment is to explore the correlation between the volume of a gas and its temperature. This relationship is described by Charles' Law, which provides a mathematical expression for the variation of volume with temperature at constant pressure:
V = kT
In this experiment, we will investigate the linear relationship between volume and temperature for air, utilizing the aforementioned equation.
Procedure
To begin, seal a 250 ml Erlenmeyer flask with the provided rubber stopper assembly in the laboratory. Use a triple beam balance to measure the weight of this assembly, ensuring accuracy within +0.01 grams. Set up the equipment according to Figure 13, placing the flask on a tripod above a Bunsen burner. Secure the flask with a clamp and add enough water to the beaker, covering the flask up to its neck. Allow the water in the beaker to boil for a minimum of 10 minutes, allowing the air inside the flask to reach the boiling point of water.
Once the flask has been heated for the required time, use a pinch clamp to seal the rubber tubing. Carefully remove the flask and its assembly from the boiling water and invert it into a sink filled with water. The sinks contain two different temperature options: a lower one near 0°C and an intermediate one close to room temperature. Release the pinch clamp, and as the air in the flask cools, water from the sink will be drawn into the Erlenmeyer flask. Keep the flask in the inverted position until you are confident that the air inside has reached the temperature of the water in the flask. Secure the pinch clamp again and remove the flask from the sink.
Determine the volume of water drawn into the flask by weighing it after removing it from the water bath. Measure the precise temperatures of the baths and also record the barometric pressure. Repeat this procedure in both the low and intermediate temperature baths. Ensure that the Erlenmeyer flask is thoroughly dried before starting each run. Finally, fill the flask with water, insert the connector, and weigh it using a triple beam balance.
Figure 13 Apparatus for the Study of Charles’ Law
Performing the experiment outlined above will yield data regarding the volume of a gas at 100°C and the volume of gas at the temperature of the water in the sink. Here are the step-by-step calculations:
1. Determine the weight of the water in the flask at the intermediate temperature. This can be done by subtracting the weight of the apparatus from the combined weight of the apparatus and the water at the intermediate temperature. The result is equal to the volume of water in the flask at this temperature, assuming the density of water to be 1.00 g/mL.
2. Determine the weight of the water in the flask at the low temperature. Similar to step 1, subtract the weight of the apparatus from the combined weight of the apparatus and the water at the low temperature. This value represents the volume of water in the flask at the low temperature.
3. Calculate the volume of air in the flask at 100°C. This can be achieved by subtracting the weight of the apparatus from the weight of the apparatus when it is filled with water. This weight corresponds to the weight of the water in the full flask, which is also equivalent to the volume of water when the flask is full. Therefore, it equals the volume of the flask itself.
4. Compute the volume of air in the flask at the low temperature. Subtract the volume of water in the flask at the low temperature (from step 2) from the volume of the flask calculated in step 3. This result represents the volume of air at the low temperature and will be denoted as V1.
5. Calculate the volume of air in the flask at the intermediate temperature. Subtract the volume of water in the flask at the intermediate temperature (from step 1) from the volume of the flask calculated in step 3. This will be referred to as the volume of air at the intermediate temperature (V2).
6. Determine the pressure of the air at the low temperature by subtracting the vapor pressure of the water at that temperature from the barometric pressure. This will be labeled as the pressure of the air at the low temperature (P1).
7. Determine the pressure of the air at the intermediate temperature by subtracting the vapor pressure of the water at this temperature from the barometric pressure. This will be referred to as the pressure of the air at the intermediate temperature (P2).
8. Calculate the volume of the air at the low temperature corrected to standard temperature and pressure (STP) conditions.
V3 = ((P1 )(V1 )) / Patm
9. Calculate the volume of the air at the intermediate temperature corrected to STP conditions.
V4 = ((P2 )(V2 )) / Patm
Plot of Data:
Create a graph displaying temperature (°C) values spanning from -273 to +100°C along the x-axis and Volume in milliliters along the y-axis. Plot the experimental values on the graph and draw a straight line that best fits the points. Avoid simply connecting the dots. Extend the graph until it intersects the x-axis and ascertain the temperature at this intersection point. This extrapolated value will represent absolute zero. Include this graph along with the report.
Report Sheet for CHARLES' LAW
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Lab / Section_________________________________
Review Questions
1. What is the objective of the lab?
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2. Explain the relationship between volume and temperature in Charles' Law.
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3. How does the setup of the apparatus contribute to the investigation of Charles' Law?
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4. Why is it important to weigh the Erlenmeyer flask and its assembly before conducting the experiment?
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5. Describe the process of heating the water in the beaker and its impact on the air in the flask.
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6. What is the purpose of immersing the flask, inverted, into the water in the sink?
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7. How is the volume of water sucked into the flask determined?
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8. How can the weight of water in the flask at different temperatures be used to calculate the volume of air in the flask?
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9. Explain the calculations involved in determining the volume of air at the low and intermediate temperatures.
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10. What factors are considered when correcting the volume of air to standard temperature and pressure (STP) conditions?
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11. How is the pressure of air at different temperatures calculated using the barometric pressure and the vapor pressure of water?
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12. What is the significance of determining the volume of air at STP conditions?
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13. What is the purpose of preparing a graph with temperature and volume values?
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14. How are the experimental data plotted on the graph, and why is it important to draw a best-fit straight line?
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15. What does the intersection of the graph with the x-axis represent in terms of temperature?
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16. How does the volume of air behave as the temperature decreases?
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17. Can Charles' Law be applied to all gases under any condition? Explain.
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18. How does the density of water affect the measurements and calculations in this lab?
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19. Discuss the safety precautions that should be taken during the lab.
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20. Why is understanding Charles' Law important in the study of gases and their behavior?
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