Ideal Gas Law Prelab

1.In order to perform the Gay-Lussac Law experiment (Part 1), what two variables pertinent to the Ideal Gas law will be kept constant for the air in the flask?

2. In order to perform the Boyle’s Law experiment (Part 2), what two variables pertinent to the Ideal Gas law will be kept constant for the air in the cylinder?

3. What are the 4 types of water used for temperature control in Part 1?

4. Give a brief description of each graph you will print out in parts 1 and 2.

Ideal Gas Law Lab

MATERIALS

Computer and Lab Pro interface / aluminum container with stopper taped on
Gas Pressure Sensor / ring stand and utility clamp
Temperature Probe / utility clamp
plastic tubing with two connectors / plastic syringe
4 1-liter plastic beakers
rubber mitt for pouring

Part 1 – The Gay-Lussac Law
Pressure vs Temperature for a confined ideal gas (i.e volume and number of moles kept constant)

Using the apparatus shown in Figure 1 (aluminum container instead of glass flask), you will place thecontainer in water baths of varying temperature. Pressure will be monitored with a Pressure Sensor and temperature will be monitored using a Temperature Probe. From the data and resulting graph, you will determine what kind of mathematical relationship exists between the pressure and absolute temperature of a confined gas. You will then use your data to find a value for absolute zero on the Celsius temperature scale. Figure 1

PROCEDURE (water at various temperatures)

1. Prepare the Temperature Probe and Pressure Sensor for data collection.

  1. Plug the Pressure Sensor into Channel 1 of the computer interface.
  2. Plug the Temperature Probe into Channel 2 of the interface.
  3. Attach one end of the plastic tubing to the stopper of the container and the other end to the Pressure Sensor. The air sample to be studied is confined in the container.

2. Open Experiment 7 folder from Chemistry with Vernier. The vertical axis has pressure scaled from 0 to 150 kPa. The horizontal axis has temperature scaled from 0 to 100°C. Note this is an event-with-entry mode; you have to click on the “keep” icon to collect data once the collect button is pushed. Note: You can choose to redo a point by pressing the ESC key (after clicking , but before entering a value). Once you’ve hit the keep button the data are permanent.

3. Prepare an ice-water bath. Put about 400 mL of cold tap water into a 1-L beaker and add ice to about 700-800 mL, or enough to cover the aluminum container up to the stopper without overflow.

4.Put about the same amountof room-temperature water from the tap into a 2nd beaker.

5. Prepare a 700-800 mL mixture of hot water and tap water (should be about 40-50 degrees) in the 3rd beaker.

6. Put about the same amount of hot water (80-90 degrees) in the 4th beaker.

7.Click to begin data collection.

8.Collect pressure vs. temperature data for your gas sample:

  1. Place the flask into the ice-water bath. Make sure the entire flask is covered
  2. Place the temperature probe into the ice-water bath.
  3. When the pressure and temperature readings displayed in the window stabilize, click . You have now saved the first pressure-temperature data pair.

7.Repeat the procedure using the room-temperature bath.

8.Repeat the procedure using the hot water-tapwater bath.

9.Repeat the procedure using the water from the hot plate.

10.Click when you have finished collecting data. Turn off the hot plate. Record the pressure and temperature values in your data table, below.

11.Since our relationship is with T, not ∆T, we must change our temperature scale to Kelvin: To accomplish this, you must create a new calculated data column for Kelvin temperature.

  1. Choose New Calculated ColumnFormula from the Data menu.
  2. Enter Temp Kelvin as the Long Name, “Kelvin” as the Short Name, and “K” as the Unit. Enter the correct formula for the column into the Equation edit box. It is “Temperature” + 273. Click .
  3. Click on the horizontal-axis label, select “Temp Kelvin” and click . Enter the Kelvin data in your data table below.

12.Click the Curve Fit button, .

  1. Choose your mathematical relationship from the list at the lower left. If you think the relationship is linear (or direct), use Linear (y = mx + b). If you think the relationship represents a power, use Power (y = Ax^b). Click .
  2. A best-fit curve will be displayed on the graph. Click . If you made the correct choice, the curve should match up well with the points. If the curve does not match up well, try a different mathematical function and click again. When the curve has a good fit with the data points, then click .
  3. Scale both axes starting with zero, double-click in the center of the graph to view Graph Options, click the Axis Options tab, and select Autoscale from 0 for both axes.

13.Print a copy of the graph of pressure vs. temperature (K), along with the information box.

14. Change the temperature axis back to °C redo the curve fit. Adjust the axes so that you can see the x-intercept, the Celsius temperature at which the pressure will be zero. This value should be calculated by using the equation of the best-fit line and setting y to zero.

Temp (°C) ______(at P = 0 kPa).

15. Print a copy of the graph of pressure vs temperature (°C) along with the information box.

16. Calculate the % difference between your value for absolute zero in degrees Celsius and the accepted value (for full credit, it should be within 15%).

DATA for part 1

Pressure
(kPa) / Temperature
(°C) / Temperature
(K)

Part 2 – Boyle’s Law Pressure vs. Volume for an fixed number of moles of an ideal gas at constant temperature
Constant Temperature PV diagrams (Isotherms)

If you provide an external force to the movable piston on a cylinder, it’s has the same result as changing the atmospheric pressure; either the temperature inside the cylinder or the internal cylinder pressure will change in response. If you push down slowly enough, the temperature inside will remain constant; only the pressure will change.

We will use the setup shown below to conduct this experiment. The “cylinder” is actually a syringe and connects directly to the pressure sensor:

1. Move the piston to position the front edge of the inside black ring (see Figure) at the 5.0-mL line on the syringe. Then attach the syringe to the gas pressure sensor. Don’t force the attachment, you only need to turn the fitting ¼ to ½ of a turn.

2. Open the experiment file by selecting the following from the file menu: Experiments, Chemistry with Vernier, Boyles Law (Expt 6). You will obtain a graph which plots pressure (kPA) vs volume (ml). Note the data collection mode is on “Events With Entry.” This mean you will have to input the volume measurement (in mL) manually for each pressure measurement.

3. Collect the pressure vs. volume data. It is best for one person to take care of the gas syringe and for another to operate the computer.

  1. Hold the piston firmly in the position shown above, with the inside ring at the 5.0 mL line, until the pressure value stabilizes.
  1. When the pressure reading has stabilized, click . Type “5.0” in the edit box. Press the ENTER key to keep this data pair. Note: You can choose to redo a point by pressing the ESC key (after clicking , but before entering a value).
  2. Continue the procedure for volumes of 7.5, 10.0, 12.5, 15.0, 17.5, and 20.0 mL.
  3. Click when you have finished collecting data and enter data in the table below, including the product of P and V, for each data pair.

4. Now we are going to choose a best-fit curve for this graph. Writing out the Ideal Gas Law in the format of our graph (y axis = constant times x axis):

P = (nRT) (V)-1

which is an inverse relationship ( i.e. P and V are inversely proportional).

5. Click the Curve Fit button, . Choose inverse from the list at the lower left. Click , and a best-fit curve will be displayed on the graph. Click .

6. If your best-fit curve does not match your data, check the value of your constant A against the product of P and V for each data pair. If one or more is not close (within 100 kPA-mL), redo the experiment. Otherwise Print a copy of the graph with the equation information.

7. Plug in the temperature probe and record the room temperature: ______

DATA For Part 2

Volume
(mL) / Pressure
(kPa) / Constant
P•V

Questions – Part 1

2.Based on the data and graph that you obtained for this experiment, express in words the relationship between gas pressure and temperature.

3.Write an equation to express the relationship between pressure and temperature (in K) for this experiment. It should start out: P = …… Use the symbols associated with the molar form of the Ideal Gas Law. Circle the symbols that were constant in this experiment:

4.According to this experiment, what should happen to the pressure of a gas if the Kelvin temperature is doubled? Check this assumption by finding the pressure at -73°C (200 K) and at 127°C (400 K) on your graph of pressure versus temperature. How do these two pressure values compare?

5. Assume that the stoppered flask holds 140 mL of air. Use the results of your Pressure vs temp (K) graph to calculate the number of moles of air in the flask. The y-intercept should be small enough (less than ±10) so that you can ignore it. Show your work below. Recall that volume in not in SI units.

Questions – Part 2

1.Based on the data and graph that you obtained for this experiment, express in words the relationship between gas pressure and volume.

2.Write an equation to express the relationship between pressure and volume for this experiment. It should start out: P = …… Use the symbols associated with the molar form of the Ideal Gas Law. Circle the symbols that were constant in this experiment:

3. According to this experiment, what should happen to the pressure of a gas if the volume is doubled? Check this assumption by finding the pressure at 10.0 mL and at 20.0 mL on your graph of pressure versus volume. How do these two pressure values compare?

4. Using the results of your PV graph (and assuming Tsyrine = Tlab , calculate the number of moles of air in the syringe (Note: neither volume nor temperature are in SI units).

6. Look up the name for a pressure-versus-volume graph for a gas at a constant temperature:

______