Practical examples of the gas laws

Practical Examples of the Gas Laws

 Objectives

• Learn and understand physical properties of gases and explain observations in terms of the kinetic molecular theory of gases.
• Plot and calculate the root mean square speed of the Carvone molecules. (Comparison with speed in vacuum).
• Estimate volume and volume change of a balloon when it goes from room temperature (RT) to liquid nitrogen temperature.
• Observe and explain behavior of gas in: a soda can, a balloon in a flask, Cartesian diver, etc., when a change in pressure or temperature is applied.

Grading

You grade will be determined according to the following:

• Pre-lab (10%)
• Lab Report Form (80%)
• TA points (10%)

Introduction

Expanding and contracting balloons, imploding soda cans, exploding marshmallows are just some of the demonstrations that are often used to illustrate the empirical gas laws and the kinetic molecular theory of gases. In this experiment, you will be performing these and other‘demonstrations’and using your understanding of the physical properties of gases to explain your observations.

There will be two demonstrations laid out at each of the seven different stations around the room and you will go as a group, half the group working at each station (you don’t need to start with #2). If your group starts with, for example station 5, you should then follow the following order: 5, 6, 7, 8, 2, etc. Your group should spend no more than 15 minutes at each station, in some cases 5 minutes is sufficient. Perform the experiment by following the instructions placed at each station. Then discuss your observations with your group. For each of the activities, it is important to ask yourself what is going on; "how can our observations be explained using the kinetic molecular theory of gases?" Remember that for some demonstrations calculations may also be required. Be thorough and precise in your explanations.

 Important Safety Notes:

Remember to use tongs, hot grips as appropriate when dealing with hot liquids, vapors and containers.

Liquid nitrogen is extremely cold, with a boiling point of $-\text{196}°$ C and if it comes into contact with skin can result in severe frostbite.

The vacuum dessicator should be regarded as a potential implosion hazard when evacuated. Handle it carefully.

When doing the egg experiment do not put the hot flask immediately in the water bath (let it for at least 3 minutes sitting on the bench) as it will crack.

Observe and record what happens in your laboratory report form and explain your observations in terms of the Kinetic Molecular Theory of Gases.

You are encouraged to discuss among yourselves possible explanations to your observations.

Experimental Procedure

Diffusion:

• The goal of this experiment is to measure the rate of diffusion of carvone, a major component of spearmint oil. We will do these trials altogether, with volunteers, at the end of the pre-lab lecture. You will all stand in a line, with the first person in the group holding the bottle of carvone and several paper towels. All four people should be 1 meter apart. You will need to know the distance each person is from the bottle of carvone. The fourth person should act as the timekeeper.
• When the timekeeper gives the signal, the first person should place a few drops of carvone on the paper towels. Record the time that it takes for each person to smell the carvone. Seal the paper towel in a plastic bag when you are finished.
• After the odor has dissipated, we will repeat the experiment twice with more volunteers.
• Using Excel plot the data in distance traveled versus time. Obtain a least squares fit ( $R^2$ , R squared value) for this data and determine from it the rate of diffusion of carvone in meters per second. Create a graph for each trial. Calculate the average of the rates for the three trials. Calculate the root mean square speed of carvone molecules at $\text{25}°$ C. Your TA will help you with this equation. Compare the result with the diffusion rate you measured.
• If they are significantly different, offer an explanation.
• Would the diffusion take place faster in a vacuum?