EXPERIMENT 12 GAS LAWS ( BOYLE S AND GAY-LUSSAC S LAW)

Transcription

1 EXPERIMENT 12 GAS LAWS ( BOYLE S AND GAY-LUSSAC S LAW) INTRODUCTION: In order to specify fully the condition of a gas it is necessary to know its pressure, volume, and temperature. This quantities are interrelated, being connected by the general gas law, so that if any two of them are known, the third is determined by the mathematical relation between them. One of the important properties of a gas is that it always tends to expand until it completely fills the vessel in which it is placed, and thus the pressure it exerts depends on the volume it occupies. To describe fully the condition of a gas it is necessary to give not only the volume but also the temperature and pressure, because they are all interrelated. The purpose of this experiment is to study two of the gas laws; that is, to develop the relation between the volume and the total pressure of a given mass of gas when the temperature is kept constant; and to investigate the variation of the pressure, of a given mass, of gas with changes in its temperature, when the volume is kept constant. the volume to the pressure, and the pressure to the temperature. THEORY In studying the behaviour of a gas under different conditions of pressure, temperature, and volume, it is convenient to keep one of these constant and to vary the other two. Thus, if the temperature is kept constant, one obtains the relation between the pressure and the volume; if the volume is kept constant, one gets the relation between the temperature and the pressure. Boyl s law: if the temperature is kept constant, the volume of a given mass of gas varies inversely as the pressure. This means that for a constant temperature, the product of the volume and the pressure of a given amount of gas is constant. Thus (Eq. 1) PV = constant or P 1 V 1 = P 2 V 2, where V 1 is the volume of a given mass of gas at pressure P 1, and V 2 is the volume at pressure P 2. The experimental test of Boyl s law consists in observing a series of different volumes, measuring the corresponding pressures, and observing how nearly constant the product of the two remains. GAY-LUSSAC LAW: if the volume remains constant, the pressure of a container of a gas is directly proportional to its absolute temperature. THE EXPERIMENT: 1. EXPERIMENTAL APPARATUS: To demonstrate the concept of BOYL S LAW (pressure vs. volume) and GAY- LUSSAC S LAW (pressure vs. absolute temperature) you will use the Pressure Sensor and the

2 temperature Probe with the Vernier Logger Pro Software and its Interface (Lab Pro). You will also find your laboratory station equipped with an Erlenmeyer flask, beaker, and heating plate. 1. EXPERIMENTAL PROCEDURE: The white stem on the end of the Gas Pressure Sensor Box has a small threaded end called a luer lock. With a gentle half turn, you may attach the plastic tubing to this stem using one of the connectors already mounted on both ends of the tubing. The Luer connector at the other end of the plastic tubing can then be connected to one of the stems on the rubber stoppers that are supplied, as shown in figure 1. Figure 1 Figure 2 Figure 3 Preparing Logger Pro for Measurements A. Boyl s law experiment: Connect the Pressure Sensor into the LabPro interface's Ch.1; Open the LoggerPro application from the desktop. Set the syringe to 20 cc volume. Connect the 20mL plastic syringe directly to the stem, as shown in figure 3, to secure the connection twist the syringe with a gentle 1/2 turn. The pressure inside the syringe is now equal to atmospheric pressure at the selected volume. Open Boyle s Law file from Physics_Experiments folder Click the Collect button and monitor the pressure in the data table. Make sure that the pressure on the syringe keeps the volume at 20 cc while your are collecting the data. When this pressure has stabilized, read the volume on the syringe and click Keep button. A data entry box will appear allowing you to enter the volume of air in the syringe; in this box you should record the syringe volume in cc (i.e. 20). Decrease the volume to 15 cc and take a new pressure measurement. Again let the pressure stabilise before you click the Keep button. Collect the pressure for the volumes of 12 cc, 10 cc, and 7 cc by following the same procedure outlined in the previous steps.

3 Click Stop once you have taken all the readings Save this data in D drive or USB drive: under a filename that consists of six characters. The first three characters should correspond to the first three letters in your last name and the last three characters should be Boy. Example Rac_Boy for Rachid. B. Gay-Lussac s law: Plug the temperature probe in Channel 1, and the pressure sensor in Channel 2. Connect the white valve stems to one end of the long piece of plastic tubing. Connect the other end of the plastic tubing to one of the stems on the rubber stoppers (figure 2). This rubber stopper should, in turn, be inserted into the Erlenmeyer flask to provide a constant-volume gas sample. Note: the 2 nd valve on the rubber stopper is shown in a closed position. (Check this?!). Insert the Erlenmeyer flask in a cold water bath of the beaker (make sure that the beaker is not too full of water, so that no water splash over). Open the GAY-LUSSAC file from the File menu. Set the experimental time to 10 minutes. Place the water baths on top of the heating plate, and immersed in the water you should have Erlenmeyer flask and the Temperature Probe. Make sure that the temperature probe is not touching the walls of the water bath. Set the heater at 3/4 of its full scale, and then turn it on. Click the Collect button to have the computer collect data for the change in pressure as a function of temperature for the period of 10 minutes. Save this data in drive E or USB drive: under a filename that consists of six characters. The first three characters should correspond to the first three letters in your last name and the last three characters should be Gls, Example Rac_Gls for Rachid. ANALYSIS OF RESULTS: A. Boyl s law experiment: In a new column of the data table from the saved Boyle s experiment file have the computer calculate the product PV for each pressure.(data new calculated column) Leave the Graph and the Data windows on your screen and close the text window. Call the laboratory instructor to check your results. Plot a second curve using the values of the pressure as the dependent variable and the corresponding values of 1/V as the independent variable. You can easily graph pressure vs. the reciprocal of the volume by clicking on the "volume" label on the x-axis of the graph, and from the list of columns that will appear; select "1/V" then click on the "autoscale button ". Using the curve fitting options in the Analyze menu, show how your results and curves verify Boyle s law. Explain the shape of the curves. B. Gay-Lussac s law: From the saved data file for the Gay-Lussac experiment, using the curve fitting option in the Analyze menu, and show how your results verify the Gay-lussac s law.

4 Explain what the slope of the curve represents. QUESTIONS: 1- Explain what effect a change in temperature will have on the Boyle s law experiment. 2- What is the barometric pressure in Ifrane? Would you expect this value to be different than the barometric pressure in Rabat? Explain your reasoning.

5 PHY 1401 LABORATORY REPORT EXPERIMENT 12 GAS LAWS (BOYLE S AND GAY-LUSSAC S LAW) NAME: DATE:. SECTION:. THIS PAGE NEEDS TO BE DONE AT HOME BEFORE COMING TO THE LAB. SESSION 1. EXPERIMENTAL PURPOSE: State the purpose of the experiment.( 5 points ) 2. EXPERIMENTAL PROCEDURES AND APPARATUS: (5 points ) Briefly outline the apparatus General procedures adopted.

6 3. DATA and ANALYSIS: Attach computer printouts from the Logger Pro Program with the Table window showing PV column, and the Pressure-versus-Volume graph: (15 points) Attach computer printouts from the Logger Pro Program with the plot of P-versus-1/V graph with the corresponding automatic curve fit: (15 points) Comparison of the graphs with Boyle s law: (5 points) Explain the shape of the curves: (10 points) Attach computer printouts from the LoggerPro Program with the Pressure-versus- Temperature graph and the corresponding automatic curve fit: (15 points) Comparison of the graph results with the Gay-lussac s law: (5 points) Slope of Pressure-versus-Temperature graph and its physical significance: (10 points)

7 CONCLUSIONS: (10 points) QUESTIONS: (5 points)