Lab 4-7.docx - Lab 4 important to know what is in the tube...

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Lab 4 important to know what is in the tube throughout the experimentPV=nRTGeneral Idea: If you add a liquid and boil it boiling point lower than waterwill vaporize and push out all air molecules and when at equilibrium the vapor is at 100 degrees C and at room pressure cooled so vapor condenses and this mass is mass of liquidfind volume by filling flask with water and using water density (m/V) at that temp to determine VLimitation- oThis final weight also accounts for weight of air and vaporoUses 100 degrees C as temp at 1 atm for boiling water but pressure is not exactly 1 atm oPV=nRT is only valid for ideal gasesResults:oFrom the moles calculated by PV=nRT and the mass weighed you can determine molar mass (mass/moles)Important NotesoDI water because boiling tab discolors beaker oYou heat the Dumas tube 5 mins after all liquid has disappeared to ensure it is all evaporated. Then weighedThis is repeated at least 3 times to ensure consistency oAcetone is used in the end to dry the tube oIt would not effect the accuracy of the molar mass if too much unknown was added (would take longer to evaporate) but it would effect if too little was added (tube would not fill)Contents of TubeoInitial Room Temp: Air Molecules + Unknown Liquid + Unknown Vapor Pressure equal to room tempoWhen Heated:Only Unknown VaporoWhen Re-cooledAir Molecules + Unknown Vapor @ equilibrium+ Unknown LiquidCan subtract out Air weight when subtracting out emptydumas tube

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