A. Demonstration Experiment Use the report sheet to record the data collected by

Question

A. Demonstration Experiment Use the report sheet to record the data collected by the laboratory instructor. Calculate the volumes by means of the appropriate gas laws and compare them with the observed volumes. Express the differences as percent error. B. Molar Mass of a Vapor Record the number of your unknown liquid (1). Place a small square of alu- minum foil over the mouth of a clean, dry 125 mL Erlenmeyer flask. Fold the foil loosely around the neck and secure with a rubber band (Figure 13.2). Use a pin to make a very small hole in the center of the foil. Determine the mass of the flask, foil cap, and rubber band (2) Place about 350 mL of water and some boiling chips in a 600 mL beaker and begin heating it to bring the water to a boil. While the water is heating, remove the foil from the Erlenmeyer flask and place about 2 mL of your unknown liquid in the flask; then replace the foil and rubber band. Clamp the flask at the top of the neck. After the water has been brought to a boil, record its temperature (3) and barometric pressure (4). If you calibrated your ther- mometer in Experiment 1, apply its correction. Insert the Erlenmeyer flask as far as possible into the boiling water, holding it by hand using the clamp. It is not necessary to clamp the flask to the ring stand. After about 4 min, remove the flask from the boiling water and examine it to see whether all of the unknown liquid has vaporized including any that condensed in the neck) If it has not, reinsert the flask into the boiling water for a few minutes. After all of the liquid has vaporized, u the clamp to remove the flask and set it aside to cool Copyright c 2015 Pearson Education, Inc PR

Explanation / Answer

1. If small amount of liquid is used , then the mass difference will be very small. error can arise from this smalll data

2.Major source of error : (i) not all the liquid is vaporized (ii) some of the vapor has escaped

3. Calculated molar mass will be higher than actual value. As the vapor will consist of liquid vapor + water vapor. The pressure you calculated will be for both.

4. Instead of water bath you have to use a heater / burner

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