MELTING POINT DETERMINATION
Purpose:
The purpose of this laboratory exercise is to identify and assess the purity of an unknown solid
organic compound by determining its melting point and comparing this number to a list of possible
compounds.
Discussion:
Answer the following questions to help direct research for prior knowledge for this lab:
1. How is the melting point of a solid defined?
2. How is the melting point of a solid used to identify the solid?
3. How is the melting point of a solid used to assess the purity of the solid?
Objectives:
In this lab, you will…
1. determine the melting point, identify and assess the purity of an unknown organic
solid.
Equipment:
Fisher-Johns Melting Point Apparatus (or)
MEL-TEMP Melting Point Apparatus (or)
Digital Melting Point Apparatus (or)
Vernier Melt Station/LabPro/Laptop/LoggerPro
Centigram Balance
Weigh boats
Mortar & Pestle
Forceps
Microscope cover glasses
Capillary tubes
Goggles
Chemicals:
Unknown Organic Solid
Acetone
Safety:
 Wear safety goggles at all times.
 Please handle the microscope cover glasses with care and return them to their case clean.
Procedure:
1. Obtain approximately 0.01 g of the chemical to be tested in a plastic tray. Using a mortar and
pestle, grind the sample into a fine powder.
2. It is suggested that a rough and quick trial run is completed to get an approximate melting point
for your unknown. Once a rough melting point is determined, allow the machine to cool to at least
15°C below the bottom temperature of the rough melting point.
3. After the rough trial, head the machine very slowly through the melting point. The slower it heats
through the melting point, the more accurate the melting point.
4. Record the temperature at which the first liquid droplets appear.
5. Record the temperature at which the last solid particles liquefy.
6. Average the two temperatures to get the experimental melting point of the solid.
Fisher-Johns Melting Point Apparatus Directions
7. Obtain eight (4 pair) microscope cover glasses.
8. Place a very small pile of the unknown compound on four microscope cover glasses. Place a
second microscope cover glass over the pile. Press glasses gently but firmly together.
9. Place one of the glasses containing the compound onto the circular depression in the center of the
melting stage.
10. Turn on melting point apparatus and begin heating the compound.
11. Run three trials after the rough and quick trial run.
12. Be sure to recycle the glass plates. See the cleanup section below.
MEL-TEMP Melting Point Apparatus Directions
7. Obtain four capillary tubes.
8. Tap the end of a capillary tube into the pile of compound. Invert the capillary and tap so that the
solid falls to the sealed end. Continue this until 3-4 mm of chemical are packed into the sealed
end of the capillary tube.
9. Place the capillary tube into the MEL-TEMP apparatus.
10. Using the heating curve provided (last page), adjust the power knob to the desired power level.
This will start the heating process. At the melting range, the temperature should increase at about
six degrees per minute or less.
11. Run three trials after the rough and quick trial run.
Stuart Digital Melting Point Apparatus Directions
7. Follow steps 1 – 2 of the MEL-TEMP directions.
8. For the rough and quick trial run, set the plateau temperature to 200°C. The apparatus will heat to
this temperature quickly, so keep an eye out to catch the approximate melting range.
9. For the remaining trials, set the plateau temperature for the bottom of the melting range. The
apparatus will heat slowly beyond the plateau temperature.
10. Run three trials after the rough and quick trial run.
Vernier Melt Station Directions
7. Follow steps 1 – 2 for the MEL-TEMP directions.
8. Turn on the laptop and open LoggerPro. Plug in the power supply to the LabPro. Plug the Melt
Station into the LabPro. Plug the power supply to the Melt Station. Attach the LabPro to the
laptop via USB cable. LoggerPro should automatically recognize that the Melt Station is
connected.
9. Place the capillary tube into one of the three slots in the top of the apparatus.
10. Click “COLLECT” on LoggerPro to begin data collection. Turn the knob on the apparatus to
“Rapid Heat” to obtain a rough melting point range.
11. Turn the knob back to the Fan/Cooling setting to cool for the first trial.
12. Once the apparatus has cooled, turn the knob to the lower end of the rough melting point range.
The apparatus will heat ~1.5°C/min through the melting range.
13. Run three trials after the rough and quick trial run.
Cleanup:
 Recycling the glass plates is absolutely necessary.
o Wipe off as much of the compound as possible with a paper towel. Rinse the glass plates
with acetone three times. Allow them to dry, and return them to their container.
 Capillary tubes can be thrown away in the red can.
BOILING POINT DETERMINATION
Purpose:
The purpose of this experiment is to determine the boiling point of an organic liquid.
Discussion:
Answer the following questions to help direct research for prior knowledge for this lab:
1. How is the boiling point of a liquid defined?
2. How is the boiling point of a liquid used to identify the liquid?
3. How is the boiling point of a liquid used to assess the purity of the liquid?
4. How do changes in atmospheric pressure affect a liquid’s boiling point?
5. How are measured boiling point values corrected for differences in atmospheric pressure?
Objectives:
In this lab, you will...
1. determine the boiling point, identify and assess the purity of an unknown organic
liquid.
Materials:
Small Test Tube
Capillary Tube
Thermometer
Rubber Band
Dennis Tube
Test Tube Clamp
Chemicals:
Thermometer Clamp
Unknown organic liquid
Bunsen Burner w/ Hose and Striker
Glycerol
Forceps
Safety:



Procedure:
1.
2.
3.
4.
5.
6.
7.
Cleanup:
1.
Wear safety goggles at all times.
Organic liquids are flammable. Do not expose to open flame. Leave all chemicals to be
tested in the fume hood.
The glycerol in the Dennis tube will get very hot. Handle it with care.
Fasten a small test tube to the side of the thermometer using a rubber band. Align the bottom
of the test tube with the bottom of the thermometer.
Break off a capillary tube ~ 2 cm long. Hold the capillary tube with forceps and melt the end
of it in burner flame to seal it. Place the capillary tube in the small test tube sealed side up.
Pour the liquid to be tested into the small test tube so that it submerges the capillary tube by
about 1 cm.
Place the thermometer with the fastened test tube in a Dennis tube. Submerge the tube in the
glycerol so that the level of the liquid to be tested is ~1 cm below the level of the glycerol.
Heat the Dennis tube slowly until a continuous stream of bubbles comes from the bottom of
the small capillary. At this point, remove the heat.
Allow the apparatus to cool. Record the temperature at the instant the steady stream of
bubbles cease to come out of the capillary tube. This is the boiling point of the liquid.
Run two more trials, making sure that the glycerol cools to at least 10°C below the boiling
point.
Discard the liquid in the organic waste bottle, and the capillary tube in the red can.
2. Rinse the inside of the small test tube once with acetone before cleaning it.