Chemical Forums

Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: futurebrewer on February 14, 2012, 03:16:18 AM

Title: Molecular Weight
Post by: futurebrewer on February 14, 2012, 03:16:18 AM

I have a question to answer for my lab and I'm not sure where how to go about it. Would appreciate any help.

A volatile liquid sample is placed in an Ehrlenmeyer flask that has been sealed except for a tiny hole that allows vapor to escape.  Upon heating, the liquid is converted to vapor that fills the flask.  Cooling the flask allows the vapor to condense back to liquid.  The mass of the condensed liquid is found to be 0.535g. The actual volume of the flask is 137.5 mL.  The temp of the flask contents is 29.2 C and the atmospheric pressure reading is 29.32 inches of mercury  From this data determine the molecular weight of the volatile liquid.

Title: Re: Molecular Weight
Post by: Borek on February 14, 2012, 04:31:18 AM

Think in terms of the ideal gas equation.

Title: Re: Molecular Weight
Post by: Arkcon on February 14, 2012, 07:28:39 AM

This is always a tough lab for students, it depends as much on performing the procedure right as on performing the calculation right.  And those are both so daunting, they affect your performance of the other. ;D Borek: has already pointed you to the ideal gas law, so start by writing the formula.  The flask, no matter how much liquid there was, had nothing but vapor in it once it was entirely evaporated.  How much vapor?  You have two answers for that question.  Pull it all together with the other data in the formula.

Title: Re: Molecular Weight
Post by: futurebrewer on February 17, 2012, 02:07:41 AM

I figured it out! Thanks!