# Exp 4(2) - Monday,Oct.11isFallbreak Tuesday,Oct....

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10/6/2010 1 Week of Oct 11 Exp 3 worksheet due Exp 4 Exp 4 TURN ON YOUR CLICKER NOW Monday, Oct. 11 is Fall break Tuesday, Oct. 12 follows a Monday schedule Monday students Exp 3 assignment, due Tuesday, Oct. 12 in lab at 1:30pm. You will do exp 4 on Tuesday, Oct. 12. Tuesday students Exp 3 assignment is due Tuesday, Oct 12 by 1:30pm You can turn it in to the Monday TAs in lab at 1:30pm You can turn it in to me earlier (Remsen 333 – slip it under my office door) You will do exp 4 on Tuesday, October19 Wednesday, Thursday, and Friday students Turn in assignment 3 and do exp 4 at your regular lab on Oct 13 15, as usual. 2 Exp 4 – Molar mass using the Dumas method MOLAR MASS: Defined as the mass of one mole of a substance. But how do you weigh a gas? You can't put a gas in a weighing pan like you did the pennies. So instead, we use a Dumas tube, which is a tube with a very narrow neck. At room temperature, the tube is filled with air at atmospheric pressure. The mass is that of the tube + air (blue dots) 3 When a volatile liquid (red) is placed in the tube, at first the liquid is in equilibrium with its vapor (red dots) and it also contains air . As the tube is heated, the liquid vaporizes and the air is swept out of the tube At temperatures of the tube. At temperatures above the boiling point of the liquid , the tube only contains the vapor molecules (red dots) at a pressure equal to the pressure in the room. 100 o C heat using a boiling water bath 4 Determine when all the liquid has evaporated. Watch the liquid level as you lower it into the boiling water. Some unknown may condense in the capillary tube and spurt out as the rest is evaporating. This is normal. Watch the rate at which it evaporates. Estimate when you think it has fully evaporated.