Molecular Weight of a Volatile Liquid
In this experiment, you will be determining the molecular weight of a volatile
liquid. A sample of gas will be introduced into a container of known volume. The
temperature and pressure of the system will also be determined. From this data,
using the ideal gas law, you can determine the number of moles of the substance
and knowing the mass of sample introduced, the molecular weight can be
determined.
Procedure (sortof):
The substance is an ether, which is a class of organic molecules that are
very volatile. You will connect a pressure sensor to a sealed container (of
which you measure the volume of after you are all done) Using a syringe, you
will remove some of the air in the system to drop the internal pressure of the
system. Then fill a smaller syringe with a an amount of ether and measure the
mass of the syringe (for weighing purposes, stick the syringe into a rubber
stopper.) Using that syringe, inject an amount of ether into the flask and
re-weigh the syringe) The mass of ether can easily be ascertained. The pressure
sensor will measure the increase in pressure. A pressure reading is taken when
the measured pressure levels off and the liquid is all evaporated (make sure)
There was an initial pressure of 'air' in the flask that is known (Pair) which is
simply the pressure reading before the start of the experiment) The final
(stabilized) pressure represent the total pressure. The pressure coming from the
unknown can easily be determined from the relationship Ptotal = Pair
+ Punk. With Punk in hand as well as T (room T), volume (what you
measure after all runs are done) you can calculate nunk. The
molecular weight can then be calculated.
Submit a short form memo lab report including all
appropriate calculations and results in tabular form. make sure to include a
%error calculation as well as your average molecular weight and standard deviation. Don't forget your standard
'How to make this a more effective learning experience' paragraph.
.
Prelab questions: (to be completed on a separate piece of recycled paper,
handed to the instructor as you enter lab)
1. An experiment was done and found that the mass of inserted vapor was 0.2193
g. The volume of the flask was determined to be 248.34 mL. The pressure before
the gas was inserted was 340.4 torr. After the liquid was introduced, the
pressure went up to 803.4 torr. The temperature of the day was 23.3 C.
(a) Calculate the number of moles of vapor inside the flask.
(b) Calculate the molecular weight of the unknown substance.
2. Make a chart to record your data for the procedure.
3. Research the MSDS for dimethyl ether and
diethyl ether. Give a brief overview
of their hazards.
~MEO 01 Nov 2005 15:57