Fall 2007 Student Comments:

Experiment #4: Melting Point

When taking your melting point, make sure to keep a close eye on the state of your compound. Talking to a neighbor may make you miss your melting point. This happened to me, and it was not fun re-doing it. They can take more than 30 minutes to complete. LV

When finding the melting point, attach the capillary tube to the thermometer with the bands provided.  Be sure and position the band above the seal of the oil tube and not below it since it can easily fall off.  The lab instructions aren't clear about this.  Also be sure that you position the capillary tube so that it is visible (i.e. not behind the thermometer).  Additionally, heat up the oil slowly.  If you heat the oil too quickly, it can really throw your results off since the oil will reach a certain temperature before the thermometer reaches that temperature.  This means that your compound will melt at a certain temperature yet the thermometer will read a temperature much lower than the actual temperature. So again, heat slowly. PN

use the mel-temp apparatus if possible instead of the oil apparatus.  The oil is messier, easier to burn yourself, and leaves much more room for error on the part of the experimenter. SP

Pay very close attention to you product because it may melt very fast before you know it and cause you to get an incorrect read on your melting point. K

Make sure that when you load your capillary tube, you get the unknown completely to the closed end of the capillary tube. I loaded the tubes but never made sure that the unknowns were at the closed ends of my capillary tubes, so when the unknowns started melting, they just leaked into the oil. PH

I want to totally reiterate what PHsaid about the capillary tubes. Be patient went loading then because they can be frustrating. Practice with it a little and grab a lot of tubes. I broke so many trying to 'tap' the tube to get the product all the way down the it to the tip of the closed end. Pre-Lab: Make sure you refer to Exp. #3 for the solubility. CR

You must include what it is/not sol. in other than H2O. EC

Make sure you pay attention to the temperature when the compound starts melting and when it ends. You should not have one temperature. In this lab, you need to provide the range of the melting point. MW

to make sure that there are no impurities within your unknown product because it can give you fluctuations within nyour results when trying to figure out the meling point which can make it hard for you to find out what your unknown is.  PL

Having too much solid in your capillary tube will not allow the sample to heat instantaneously, as it should. It will take too long throwing off your melting point range (more than 0.5 - 1 degree). Be sure to keep the sample in capillary to about 1-2 mm. RH

In this lab be careful with your Thiele tube because your gloves will have some oil on them from loading and reloading your tubes, and this could cause accidental slippage of your Thiele tube when you dissasemble your lab at the end.  EP

Thiele tubes are very delicate and easy to break. Be very careful when loading your samples into the tube and also when attaching the tube to the thermometer.  YM

When setting up your melting point apparatus, make sure that you attach your tube in a way where you can clearly watch your product while you are waiting for it to melt. When the tube was attached to the thermometer, it was hard to see the product and by the time you realized, your product melted and you have to do it again. MFL

Asking another individual to help you attach capillary tubes to the thermometer within the band is beneficial.  With oily hands, accidents are just bound to happen and sample is bound to be lost due to broken capillary tubes.  Also, hot glass is not friendly glass!!!!  Do not place thiele tubes directly in the flame for too long, broken glass that is oily is a pain to clean.

As interesting as it was to use the Thiele tube to determine the melting point maybe it would be better to have students use the machine that determines the melting point rather quickly.  That way time could be spent doing another interesting experiment. EP

When attaching thiele tube and thermometer, remember that you are working with glass!!! Althought they are hard to attach, if you apply to much pressure when trying to attach the band, the melting point capillary tubes will snap, and could potentially cut you...causing you to have to make a vist to the nurse to have her fish out the glass, not fun. AP