report on unknown determination

Select one unknown liquid and one unknown solid. Record the unknown number and physical appearance for each
in your notebook. Use your samples wisely because if you run out- tough luck. It is possible that the liquid may
evaporate over time so keep it tightly sealed when stored (for liquids, wrap vial with parafilm when storing over the
week).
Melting Point
Load a capillary tube with sample by pushing the open end of the tube into the sample. You only want about a 1-2
mm tall sample in the tube- not too much, or a broader mp will be obtained! You also only have a limited amount
of sample! Locate the glass tube used for packing samples and repeatedly drop the tube through a vertical glass tube
(closed side down) until the sample is firmly packed at the closed end of the tube. Use one of the melting point
apparatuses to determine the melting point. Your goal is to have a rate of heating of 1-2 degrees per minute at the
time that your sample melts. But at this rate, it could take you a long time to get to a high temp from room temp.
To save time, you may choose to prepare two samples and heat the first very quickly to get an idea of the
approximate mp and then make sure that you are heating slowly during that temperature range on the second run.
The melting point is actually not a point, but usually a pair of temperatures: the first value is noted when the first
drop of liquid is formed and the second value is noted when the entire sample has formed a clear liquid. Melting
points are always reported using both temperatures. When finished, there is a special container in the lab for
disposal of broken glass and used mp tubes.
Simple distillation
Place all of your liquid unknown in your 25 or 50 mL round bottom flask and distill it using a distillation set up as
described in lab 2.
Once you receive the go-ahead to proceed, start the stirring, adjust the power setting on the variostat as needed to
maintain a slow to moderate drip of distillate in the receiving flask. Monitor (and record in your notebook) the
temperature as you collect distillate using a vial. The low boiling impurity will distill over first. Your unknown will
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then follow, which you should collect in a separate vial or vials. You should also record its bp range. The optimal
bp for your sample is typically when a constant point is reached. You should distill most of your sample over, but
do not distill it all (i.e, do not let your original flask go dry!-this can cause a fire). Before it goes dry, remove the
heat source by raising the clamp up that’s holding your flask or by lowering your stirplate (by removing the wooden
block). Allow it to cool before you disassemble the apparatus. You may then use your unknown liquid for other
tests. Note: your thermometer should be calibrated at some point by placing it in the boiling water bath that will be
set up in the lab. Your original bp should be labeled as uncorrected; your adjusted bp should be labeled as corrected.
Infrared Spectroscopy
The IR spectrometer is located in room E3003. You should get an IR on both your liquid and your solid unknown.
To load the sample onto the instrument, you need a pipet for the liquid and a spatula for the solid. Make sure your
clean the instrument after each use with acetone.
Determination of density
Determine the density of your unknown liquid. This can be done by determining the mass of 1.00 mL of your liquid
sample (using a 1.00 mL pipet, place 1.00 mL into a tarred vial or flask and weigh the sample). Determination of
density may allow you to rule out a choice in some cases (and thus give you another argument for making your
case).