Gas Lab

Gas Laws

Tairuo Ge

03/24/11

Chemistry

Partner: Danny, Shyla

Introduction

The early gas laws were developed at the end of the 18th century, when scientists began to realize that relationships between the pressure, volume and temperature of a sample of gas could be obtained which would hold for all gases. Gases behave in a similar way over a wide variety of conditions because to a good approximation they all have molecules which are widely spaced, and nowadays the equation of state for an ideal gas is derived from kinetic theory. The earlier gas laws are now considered as special cases of the ideal gas equation, with one or more of the variables held constant.

In the first lab of the experiment, students determine the relationship between the pressure and volume of a confined gas, which is the Boyle’s law. Boyle's law shows that, at constant temperature, the product of an ideal gas's pressure and volume is always constant.  It was published in 1662. It can be determined experimentally using a pressure gauge and a variable volume container. It can also be found through the use of logic; if a container, with a fixed amount of molecules inside, is reduced in volume, more molecules will hit the sides of the container per unit time, causing a greater pressure. Boyle’s Law: P1V1= P2V2

In the second lab of the experiment, students determine the relationship between the pressure and the Temperature when the amount of gas are constant. The pressure (or Gay-Lussac's) law was found by Joseph Louis Gay-Lussac in 1809. It states that the pressure exerted on a container's sides by an ideal gas is proportional to the absolute temperature of the gas. This follows from the kinetic theory—by increasing the temperature of the gas, the molecules' speeds increase meaning an increased amount of collisions with the container walls. Use the combined gas equation law:

P1V1/T1=P2V2/T2

Part 1: Pressure-Volume Relationship in Gases

Equipment

Computer Vernier gas pressure sensor

Vernier computer interface 20 mL gas syringe

Logger Pro

Procedure

1. Set up the data table in the lab notebook.

2. Click “Collect” to begin data collection.

3. Move the piston to position the front edge of the inside black ring at the 5.0 mL line on the syringe. Hold the piston firmly in this position until the pressure value stabilize.

4. Record the pressure and volume on the notebook. Remember add 0.8 mL to the syringe readings.

5. Move the piston to the 7.0 mL, 9.0mL, 11.0mL, 13.0mL, 15,0mL, 17.0mL and 19.0mL. Repeat the procedure 3 and 4.

6. Click stop when students finish collecting data.

Diagram

Data

Observation

If students don’t hold the syringe carefully, the pressure changes all the time.

Analysis

1. Create a graph of P vs. V.

2. From the shape of the curve in the plot of pressure vs. Volume, do you think the relationship between the pressure and volume of a confined gas is direct or inverse? Explain.

The relationship between the pressure and volume of a confined gas is inverse. Because it is a curve to connect those points.

3. Based on your data, what would you expect the pressure to be if the volume of the syringe was increased to 40.0mL? Explain to support your answer.

5.8mL * 184.00kPa = 40mL* P2

P2 = 26.68 kPa

Because it is inverse, the P * V should be constant.

4. Based on your answer to Question 2, choose one of these formulas and calculate k for the ordered pairs in your data table (divided or multiply the P and V values). Allowing for some experimental variation, is the value of k fairly constant?

K = PV

5.8mL * 184.00kPa= 1067.2 mL kPa

7.8mL * 141.50kPa = 1103.7 mL kPa

9.8mL * 113.99 kPa = 1117.1mL kPa

11.8mL * 93.40kPa = 1102.12mL kPa

13.8mL * 79.80kPa = 1101.2mL kPa

15.8mL * 70.50kPa = 1113.9mL kPa

17.8mL * 61.8kPa = 1100.0mL kPa

19.8mL * 54.5kPa = 1079.1mL kPa

5. Using P, V, and k, write an equation representing Boyle's Law. Write a verbal statement that correctly expresses Boyle's law.

PV = k

At constant temperature, the product of an ideal gas's pressure and volume is always constant. 

Part 2

Equipment

Computer Vernier computer interface Logger Pro

Vernier gas pressure sensor Vernier temperature probe ice

plastic tubing with two connectors rubber stopper assembly hot plate 125mL Erlenmeyer flask ring stand utility clamp four 1 liter beaker

Procedure

1. Set up the data table in students' notebooks.

2. Click "collect" to begin data collection.

3. Place the flask into the hot-water bath. Place the temperature probe into the hot-water bath.

4. When the readings are stable, record the data in the notebook.

5. Repeat step 3 and 4 using the room-temperature bath.

6. Repeat step 3 and 4 using the boiling-water bath.

7. Repeat step 3 and 4 using the iced-water bath.

Diagram

Data

Analysis

1. Create a graph of P vs. T (in Kelvin).

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

The pressure exerted on a container's sides by an ideal gas is proportional to the absolute temperature of the gas.

3. Based on your answer to Question 2, choose one of these formulas and calculate k for the four ordered pairs in your data table(divided or multiply the P and T values). How "constant" were your values?

K=P/T

Hot: k=106.38/319.8=0.33

Room: k=95.80/297.1=0.32

Boiling: k=116.10/360=0.32

Iced: k=91.6/278.7=0.33

It is constant.

4. Convert the following pressure and temperature values.

A. 375mmHg = 0.49atm

375mmHg/760mmHg/1atm=0.49atm

B. 3.5atm = 2660mmHg

3.5atm*760mmHg/1atm=2660mmHg

C. 275kPa = 2.7atm

275kPa/101.3kPa/1atm=2.7atm

Conclusion

Part one of the experiment determines the relationship between the pressure and volume of a confined gas. And part two of the experiment determines the relationship between the the pressure and the temperature of a confined gas. Students study the relationships and learned to find the mathematical relationship using the data and graph.

After knowing the relationships, students can get the sense of the danger which could occur in high temperature and small volume of a space. It helps to make students know the importance of safety.

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