H2_IdealGasLaw

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General Physics I LabH2 Ideal Gas Law

General Physics I Lab

H2 Ideal Gas Law

PurposeIn this experiment, you will study the relationship between pressure, volume and temperatureof a gas in a container.

Equipment and components

Science Workshop 750 interface, absolute pressure sensor (sensor box attached withthree-way valve), 20 ml plastic syringe, temperature probe with handheld readout unit, glasscylinder with plastic tubing, water bath, glass rod, stand with 2 sets of clamp & boss head, icetray with shovel.

Background

Unlike a solid or a liquid, the state of an amount of gas of mass m is determined by its

pressure P, volume V, and temperature T. In general, the equation that relates these threequantities, called the equation of state, can be very complicated. However, if the gas ismaintained at a low density (or low pressure), the equation of state is quite simple and can befound experimentally. Such a low-density gas is commonly referred as an ideal gas. Theequation of state for an ideal gas can be written as:

PV = nRT,

where n is the number of moles of gas in the sample and R = 8.314 J/molK is called theuniversal gas constant. This ideal gas law states that for a given amount of gas at constanttemperature, the pressure of the gas is inversely proportional to its volume. When the volumeof the gas remains constant, the pressure of the gas becomes directly proportional to theabsolute temperature.

Procedure

Part I: Relationship between pressure and volume at constant temperature

In this part of the experiment, you will use a pressure sensor to measure the pressure of a gasinside a syringe as the volume of the gas changes.

Computer and equipment setup

1. Connect the Science Workshop750 Interface to the computer; turn on the interface boxand the computer.

2. Connect the DIN-5 plug of the Pressure Sensor toAnalog Channel A of the interface box.

Figure 1 Setup of Part I experiment

3. Connect the plastic syringe to one of the three-way valve stems as shown in Fig. 1. Alignthe valve control handle to the unused stem. Check that the syringe and the pressuresensor have a secured seal by pushing the piston by a volume of 5 ml. You should feelresistance when pushing the piston if no leakage occurs.

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4. Open the H2-I program in the course folder. The program will open with graphdisplays of Pressure (kPa) versus Volume (ml), Pressure (kPa) versus Inverse Volume[1/V] (ml

-1) and a table of Volume and Pressure.

5. Perform sensor calibration as follows:(a) Click the Setup button to open the Experiment Setup window, and then click the

button Calibrate Sensors to open a window.

(b) Enter a value of 0.06 in the Calibration Point 1, Sensor Value (in V) and a value of0 in the Standard Value(in kPa). This point is set for you beforehand with amechanical vacuum pump applying a pressure less than 0.01 kPa to the pressuresensor.

(c) Allow the pressure sensor to reach atmospheric pressure by turning the ValveControl Handle to the stem connected to the syringe as shown in Fig. 2. Enter thevalue of atmospheric pressure (you can read it from the barometer in the lab) in theCalibration Point 2 (in kPa). Then, press the Read From Sensor button to recordthe corresponding voltage output from the pressure sensor.

NOTE: You need to perform sensor calibration whenever the program is re-opened.

Figure 2 Position of Valve Control Handle used for sensor calibration

6. Set the Sample Rate of the pressure sensor to 10 Hz in Experiment Setup window.7. The volume data (in ml) are set as Manual sampling keyboard data and you need to

measure it manually and enter the value. You may check it by clicking the Experimentmenu and selecting Set Sampling Options.

Data recording

1. Allow the syringe to reach atmospheric pressure by aligning the Valve Control Handle tothe stem connected to the pressure sensor box as shown in Fig. 3a. Position the end of thepiston to the 20.0 ml mark. Then, close the unused stem by aligning the Valve ControlHandle to this stem as shown in Fig. 3b. Now, the pressure inside the syringe is equal toatmospheric pressure, and you are ready to start data recording.

Figure 3 Positions of theValve Control Handle



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2. Click the Start button to start the data recording. The Start button will become aKeep button, and Run #1 will appear in the Data List.

3. Make sure that the piston is right at the 20 ml mark, wait 1-2 seconds for the pressure tostabilize. Click the Keep button to open a Please enter a value area. It prompts for akeyboard input of the volume data. Enter 20 in the Please enter a value area. Click

OK to record the value. The entered value of volume and the measured pressure by thesensor will appear in the Table.

4. Slowly push the piston to the 18.0 ml mark. As the pressure stabilizes, click the Keepbutton, enter 18 and then click OK to record the value. The entered second value ofvolume and the measured pressure will appear in the Table.

5. Repeat the measurements by reducing the volume by 2.0 ml each time, until the lastentered value of volume reaches 6.0 ml.

6. Click the Stop button to stop data recording.7. Export the Pressure versus Volume data and save the data as a text file.8. Printthe pressure-versus-volume data and paste the table in your lab report.9. Repeat steps 1 to 8, but start with the piston at the 6.0 ml mark. Make sure that the

pressure inside the syringe is equal to atmospheric pressure at the beginning (step 1).Increase the volume of air in steps of 2.0 ml until the last entered volume reaches 20.0ml.

Data analysis

1. Click on the Graph of Pressure vs. Inverse Volume to make it active. Rescale the graphwhen necessary.

2. Use the curve fitting tool to perform linear fits for the two sets of data.3. Printthe pressure vs. inverse volume graph (with two sets of data) together with your

fittings as solid lines. Paste the graph in your lab report.4. Record the values of the coefficients b (the y-intercept) and m (the slope) for the two

sets of data. Include appropriate units for b and m in your lab report.

Part II: Relationship between pressure and temperature at constant volume

In this part of the experiment, you will use a pressure sensor to measure the pressure changeof a gas as a function of temperature.

Computer setup

1. Connect the computer interface and the pressure sensor as in Part I.2. Open the H2-II program in the course folder. The program will open with a graph

display of Pressure (kPa) versus Temperature (C), a digital display of Pressure, and atable of Temperature and Pressure.

3. Perform the sensor calibration as follows:(a) Click the Setup button to open the Experiment Setup window, and then click the

button Calibrate Sensors to open a window.

(b) Enter a value of 0.06 in the Calibration Point 1, Sensor Value (in V) and a value of

0 in the Standard Value(in kPa). This point is set for you beforehand with a



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mechanical vacuum pump applying a pressure less than 0.01 kPa to the pressuresensor.

(c) Allow the pressure sensor to reach atmospheric pressure by turning the ValveControl Handle to the stem connected to the syringe as shown in Fig. 2. Enter thevalue of atmospheric pressure (you can read it from the barometer in the lab) in the

Calibration Point 2 (in kPa). Then, press the Read From Sensor button to recordthe corresponding voltage output from the pressure sensor.

4. On the Experiment Setup window, select the Med (x10) in the menu right under theSample Rate. This will increase the sensitivity of the pressure sensor (since the changein pressure is small in part). Set the Sample Rate of the pressure sensor to 1 Hz.

5. The temperature (in C) data are set as Manual sampling keyboard data, and you need tomeasure it manually and enter the value. You may check it by clicking the Experimentmenu and selecting Set Sampling Options.

Equipment setup and data recording

1. Disconnect the syringe from the stem of the three-way valve. Then connect the whitethreaded adapter end of the plastic tubing to the stem. The other end of the plastic tubingis connected to the neck of the glass cylinder, as shown in Fig. 4.

2. Place the glass cylinder and the temperature probe in the water bath with clamps and astand. Keep the cylinder completely submerged in water.

3. Start with hot water at ~80 C in the water bath.CAUTION: Work carefully with hot water.

4. Allow the glass cylinder to reach atmospheric pressure by turning the valve controlhandle to the stem connected to the pressure sensor box as shown in Fig. 3a. Stir thewater with a glass rod for about half a minute until the temperature of water and airinside the glass cylinder reaches equilibrium. Then turn the valve control handle theposition as shown in Fig. 3b.

Figure 4 Setup of part II experiment

5. Click the Start button to start data recording. The Start button will become a Keepbutton, and Run #1 will appear in the Data List.

6. Click the Keep button to open a Please enter a value area. It prompts for a keyboardinput of the temperature data. Watch the temperature reading of the handheld unit. When



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the temperature becomes stable in a few seconds, enter the value of temperature (in C)in the Please enter a value area. Click OK to record the value. Do not stop recording.

7. Lower the temperature of the water bath by adding some ice flakes. Continuously stir thewater in the bath. If the container becomes too full, dump out some water using adropper. Make sure that there is enough water to keep the glass cylinder completely

submerged. Reduce the temperature by 5-10C in each step and repeat the measurementas outlined in step 6.

8. Repeat steps 6 and 7 until the temperature of the water bath reaches ~0 C. Then click theStop button to end recording.

9. Export the Pressure versus Temperature data and save the data as a text file.10.Printthe pressure-versus-temperature data and paste the table in your lab report.Data analysis

1. Rescale the graph when necessary.2. Use the curve fitting tool to perform a linear fit.3. Printthe pressure vs. temperature graph together with your fitting as a solid line. Paste

the graph in your lab report.

4. Record the value of the coefficients b and m with appropriate units in your labreport.



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Name

Date

Lab session

(Day & time)Lab partner

H2 Ideal Gas Law Lab Report

A. Answer the following questions BEFORE the lab session (5 pts each)

1. How is the number of moles n of a substance related to its mass m?

2. In Part I of the experiment, you will measure the pressure change of a gas inside a syringeas the volume of the gas is reduced. What happens to the temperature of the gas? Underwhat condition you can maintain the temperature of the gas to be constant?

3. A common material for cushioning objects in packages is made by trapping bubbles of airbetween sheets of plastic. This material is more effective at keeping the contents of thepackage from moving around inside the package on (a) a hot day, (b) a cold day, or (c)either hot or cold days?



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B. Results and data analysis

Part I: Relationship between pressure and volume at constant temperature

Paste the two sets of the pressure-versus-volume data here (20 pts)

Paste the pressure vs. inverse volume graph here (12 pts).

y-intercept, b Slope, m

Compression

Expansion



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Part II: Relationship between pressure and temperature at constant volume

Paste the pressure-versus-temperature data here (10 pts)

Paste the pressure vs. temperature graph here (10 pts)

Values of the y-intercept, b = ______________________, and

the slope, m = __________________________



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C. Answer the following questions after the experiment (6 pts each)

4. Compare the fitted values of the y-intercept b and the slope m for the two sets of datain Part I. Do they obey the ideal gas law? Explain. (6 pts)

5. Write down the fitted equation for the measured pressure vs. temperature graph in Part II.Find the value of T when P = 0. What is the physical meaning of this value?

6. Discuss possible sources of error and limitations in the experiments.



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D. Summary of the experiment (15 pts)Summarize what you have done and your interpretation of the results, especially in respect to

how they match the goal of the experiment and what you have learnt from this experiment

(2-3 paragraphs, less than 450 words).

H2_IdealGasLaw

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