0.10 Physical properties of gases

After the odor has dissipated, repeat the experiment twice.

Using Excel plot the data in distance traveled versus time. Obtain a least squares fit (R 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 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?

Note: You should spend no more than one-half hour preparing the plots. Please stagger yourselves so that everyone has an opportunity to get to the computer stations.

Gas laws in a soda can:

Pour 15 mL of water into an aluminum soda can. Set the can on a hot plate and turn on to a high temperature setting. While the can water heats, fill a 1000-mL beaker with cold water (You may have a metal tin set out for this purpose). Continue heating the can until the water inside boils vigorously and until steam escapes from the mouth of the can for about 20 seconds.

Using the hot grips to grip the can near the bottom, quickly lift the can from the burner and invert (so water covers the mouth of the can) it in the beaker of cold water. Describe what happens. Explain why it happens. You may repeat this experiment using a second soda can if you wish. Why is it necessary to invert the can in the water? What would happen if a rigid container were used?

 Balloon in liquid nitrogen:

Review the safety notes above regarding the handling of liquid nitrogen.

Inflate a balloon and tie the end (Several balloons may have already been inflated and tied). Using tongs, place the balloon in a Dewar flask containing liquid nitrogen. After the balloon stops changing size, remove it from the Dewar and allow it to warm to room temperature. Observe and record the changes (you should be able to measure the radius and estimate volume).

Estimate the size of the balloon in liters. What is the pressure inside the balloon before it is placed in the liquid nitrogen? What is the pressure inside the balloon after it is placed in the liquid nitrogen? Use the ideal gas law to calculate the percent change in volume expected on going from room temperature to liquid nitrogen temperature. Is the volume of the cold balloon consistent with what you calculated, or is it larger or smaller? Suggest an explanation for your observation. Explain all of your observations in detail using the kinetic molecular theory of gases. How does the liquid nitrogen cool the gas in the balloon?

Tygon tube in liquid nitrogen:

Review the safety notes above regarding the handling of liquid nitrogen. Place a 2 foot long tygon clear tube in a Dewar with liquid nitrogen. Observe what happens and explain.

Balloon in a flask:

Place about 5 mL of water in a 125-mL Erlenmeyer flask. Heat the flask on a hot plate until the water boils down to a volume of about 1 mL. Meanwhile, inflate a balloon and then let the air out (this may not be necessary if balloons on table have been previously used). Remove the flask from the heat, hold it with a towel, and immediately place the open end of the balloon over the mouth of the flask. Observe the effect as the flask cools. Can you get the balloon back out again? If you can, How?