Ideal Gas Law CHEM 251 Week of October 25 th, 2010 Alexis Patanarut

For the week of November 1 st, 2010 Experiment: Absorption Spectroscopy, pp Quiz: material in lab manual Due next week: Ideal Gas Law lab report

Overview A sample of an unknown metal will be reacted with HCl, producing hydrogen gas and a water- soluble metal chloride salt. Unknown Metal #1 and #2: M(s) + 2HCl(aq)  MCl 2 (aq) + H 2 (g) Unknown Metal #3: 2M(s) + 6HCl(aq)  2MCl 3 (aq) + 3H 2 (g) This gas will be collected and its volume will be measured. Using the Ideal Gas Law, n (number of moles of gas produced) will be determined.

Procedure part I: Constructing the Apparatus 1.Fill a 1L beaker with tap water up to the 900mL mark. 2.Fill a 50mL graduated cylinder with water and place a piece of weighing paper over the mouth of the cylinder. Holding the weighing paper in place, quickly invert the cylinder and place it into the 1L beaker. Temporarily clamp the cylinder in place. 3.Thread the rubber tubing of a pre-assembled stopper/gas delivery system under the water line and into the mouth of the inverted cylinder. Make sure this tube is in far enough so that it will not come out during gas collection. 4.Place 10mL of 6M HCl solution into a medium test tube. Place this test tube into a 250mL beaker. Place the stopper on the test tube, taking care not to let the tube slip out of the cylinder. The fit should be snug and prevent any gas leakage.

Procedure part II: Some Preliminary Measures 1.Obtain your unknown metal and measure the mass of the sample to 3 decimal places. Prepare your sample for reaction by either folding or rolling it carefully so that it will drop into the test tube without become caught on the side of the tube. 2.Obtain readings for the temperature of the room and atmospheric pressure. Convert these values into the same units to use with the R constant L*atm/mol*K. 3.Before you being the lab, make sure that you subtract any trapped air that could have gotten into the cylinder during the process of inverting it into the beaker. Remember that you are reading the cylinder upside-down as you are doing this. Initial start volume should be subtracted out after gas collection is complete by V f - V i.

Procedure part III: The Experiment Itself 1.Begin gas collection by carefully adding the metal sample into the acid solution. Place the stopper IMMEDIATELY afterwards and make sure the fit is snug. Wait until the metal completely dissolves before continuing. 2.Once the metal sample has dissolved, carefully remove the tube from the mouth of the graduated cylinder. 3.The level of the water inside the cylinder will be either somewhat above or below the level of water in the large beaker, so you will have to loosen the clamp holding the cylinder and raise/lower the cylinder BY HAND until the water level inside and outside the cylinder is the same. Record the volume. 4.Do at least two more trials using the same unknown metal. Your sample of 6M HCl should be enough to dissolve several more metal samples, so you will only need to refill the water in the beaker as needed, re-invert the cylinder, and replace the gas delivery tube into the mouth of the cylinder. 5.Use the data collected to determine n and use the value to identify the unknown metal.

Your lab report should include the following: Raw data table (as downloaded) Class results data table Sample calculations –n for your unknown metal sample –determination of the molecular weight of your unknown metal sample –average of the three molecular weights For your Discussion/Conclusion section, answer: –Questions 1 and 3 in the experiment handout (Further Questions for Thought and Review) and all of the questions in the second handout (data handout)