Question

how would you measure P,V,T relationships in a laboratory?

Answer 1

The primary objective of this experiment is to determine the relationship between the pressure and volume of a confined gas. The gas we will use is air, and it will be confined in a syringe connected to a Gas Pressure Sensor (see Figure 1). When the volume of the syringe is changed by moving the piston, a change occurs in the pressure exerted by the confined gas. This pressure change will be monitored using the Gas Pressure Sensor. It is assumed that temperature will be constant throughout the experiment. Pressure and volume data pairs will be collected during this experiment and then analyzed

OBJECTIVES

In this experiment, you will

·    Use a Gas Pressure Sensor and a gas syringe to measure the pressure of an air sample at several different volumes.

·    Determine the relationship between pressure and volume of a gas and describe that relationship with a mathematical equation

·   Use LoggerPro software to collect data, analyze the data, and create useful graphs to interpret the data.

MATERIALS

Computer                                                              Vernier Gas Pressure Sensor

Vernier computer interface (Lab Pro)                    20 mL gas syringe

Vernier Logger Pro software

PROCEDURE

1.   Log in to the laptop computers using your normal MEID username and password.

2.   Open the Logger Pro software.

3.   Change the pressure units from kPa to atm.

4. Position the piston of a plastic 20 mL syringe so that there will be a measured volume of air trapped in the barrel of the syringe (5.0 mL is a good place to start). Attach the syringe to the valve of the Gas Pressure Sensor, as shown below. A gentle half turn should connect the syringe to the sensor securely. Note: Read the volume at the front edge of the inside black ring on the piston of the syringe, as indicated by the arrow below.

5.   With the syringe connected to the Gas Pressure Sensor press the green button.

6.   Allow the air in the syringe to equilibrate with the Gas Pressure Sensor for a minute, then press the blue button. A window will pop up, type in the volume in the syringe as 5.0 mL, then click “OK”.

7.   Move the piston in the syringe by 2mL to a larger volume (do not move to smaller volumes). When the pressure reading is stable press the blue button. In the pop-up window, type in the volume in the syringe to the nearest 0.5mL, then click “OK”.

a. The syringe may have a leak that allows air to enter while you are recording the data. If the pressure does not stabilize, but slowly goes up, the lowest pressure possible.

8.   Measure the pressure of the air in the syringe at various volumes. The best results are achieved by collecting at least seven data points. Move the piston of the syringe about 2mL, when the pressure stabilizes at the new volume, press the blue button again and type in the new volume. Continue in this manner, moving the piston an additional 2mL each time.

9.   When all of your data points have been collected, then press the red button.

PROCESSING THE DATA

1.   One way to determine if a relationship is inverse or direct is to find a proportionality constant, k, from the data. If this relationship is inverse, k = P * V. If it is direct, k = P / V. Insert two new calculated columns into your data table: Pressure * Volume and Pressure / Volume.

2.   The graph that was created during data collection is a curve. A more helpful type of graph is a straight line. In order to create a graph with a straight line plot, a new calculated column for 1/Volume will need to be created.

3.   Insert a new graph of Pressure vs 1/Volume. Make sure that the new graph has an appropriate title, and that 1/V is being plotted along the x-axis and Pressure is being plotted along the y-axis.

4.   Determine the slope of the line in the new graph. The slope of the line will be equal to the value of the proportionality constant, k.

a. The equation for a line is : y = (m*x) + b. For the graph you have created: y = Pressure, x =1/Volume, m (the slope) = k, and b (the y-intercept) = the value in the box on the graph