Molar Mass of a Volitile Liquid - Molar Mass of a Volatile...

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Molar Mass of a Volatile Liquid September 22, 2005 Introduction The purpose of the experiment was to find the molar mass of a liquid by heating it so it turns into a gas. This was done by the Dumas method. A sample of gas must be trapped in a container and made sure that the gas is at atmospheric pressure. The liquid before it is turned into gas must have a higher boiling point above room temperature and a lower boiling point than water. The procedure used in this experiment is slightly different than the real experiment using the Dumas method. In the Dumas method, a glass bulb is used for the container of the volatile liquid, instead of an Erlenmeyer flask. The bulb is heated around boiling water to vaporize the liquid. Since the volume of the vapor formed at 100 o C and pressure is greater than the volume of the bulb, the vapor begins to push out all the air. When all the vapor is seen exiting the bulb, the opening of the bulb is sealed with a flame. If the bulb is sealed too early, the bulb will contain too much vapor. If the bulb is sealed too late, the bulb will contain too little vapor. After the bulb has been cooled and weighed, the volume of the bulb is determined by submersing in a water bath and by breaking the sealed tip of the bulb. The experiment involved using the ideal gas law, which is PV=nRT . With this equation the number of moles can be calculate if the other stuff is known which can lead to the determination of the molecular weight of the volatile liquid. For this experiment, the vapor is assumed to be an ideal gas, but no gases are ever ideal in behavior. Safety
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When the beaker was done being heated with the hot plate, beaker tongs were used to empty out the hot water to avoid being burned. The beaker was not to be washed out immediately after use because the beaker might have broken. The hot plate got very hot and was left out for it to cool after it was used. Procedure Water was added to a 500 mL beaker and was half filled to leave some run for boiling. A flask was attached to a clamp and was put inside the beaker. Water was added around the flask, leaving some room for the water to boil. It was made sure that no water got inside the flask. The flask was taken out and dried with paper towels. The beaker was then heated using the hot plate. Three boiling chips were added to the water to prevent it from boiling out of control. As the water was being heated the flask was being prepared. A
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This note was uploaded on 04/14/2008 for the course CHEMISTY 10101 taught by Professor Denofrio during the Spring '08 term at University of Illinois at Urbana–Champaign.

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Molar Mass of a Volitile Liquid - Molar Mass of a Volatile...

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