Chem 142 Lab 5

There are only a few components for the experimental setup. You will use a gas density flask, lead ring, rubber flask cap, and beaker, along with a ringstand and iron ring that can be found in the lab.

After you are sure that you have a dry gas density flask, cap the flask and weigh the flask and cap on a balance. Record the mass in your notebook. Your TA will then introduce an unknown sample into your flask. Record the ID # of your unknown in your notebook.

You will then immerse the uncapped gas density flask in a beaker containing water and hold it down with a lead ring. You will be heating the water in the beaker to boiling, using a Bunsen burner, in order to vaporize the unknown sample in the flask and heat the vapor to the same temperature as the boiling water. The "rubber policeman" cap must remain off throughout the heating process.

Once you have removed the heat and capped the flask, you will let the flask cool to room temperature. As this happens, the sample that became vapor during the heating, will condense back to a liquid, creating a partial vacuum in the flask. Be very careful as you handle the flask at this point. Once the flask is at room temperature, you will weigh the flask, cap and vapor and record the mass in your notebook. Repeat these steps for three trials, but after weighing the flask, cap, and vapor for the 3rd trial, do not immediately remove the cap. You will use the partial vacuum in the flask to help fill it with water so that you can determine the volume of the flask.

Place the capped end of the flask in water that has come to room temperature in a trough. Carefully remove the cap and the flask should start to fill with water. It will not fill completely, but your TA can help you fill the neck of the flask. Dry off the outside of the flask and weigh the flask, cap, and water and record the mass in your notebook. Your TA will demonstrate how to remove the water from the flask.