Experiment #2 Boiling point and melting point determination
London dispersion.
What is the dominant intermolecular force in Naphthalene?
Inside the capillary tube, the sample is slowly being heated, and to ensure enough and accurate time for the heat to transfer through the particles of the sample, the amount of the sample is kept small.
Why do you need a small amount of sample for melting point determination?
Liquid paraffin or vegetable oil has a higher boiling point than water. Liquid paraffin has a boiling point of higher than 370°C.
Why is liquid paraffin used instead of water?
It should be continuously stirred gently and heated slowly to ensure uniform heating.
Why should the paraffin bath be continuously stirred during heating?
Otherwise, the observer may not be able to record the exact temperature because the sample will also be heated quickly.
Why should the paraffin bath be heated slowly?
Melting Point
defined as the temperature at which the solid exists in equilibrium with its liquid phase under an external pressure of one atmosphere.
Boiling Point
temperature at which the pressure exerted by the surroundings upon a liquid is equaled by the pressure exerted by the vapour of the liquid;
1. Capillary Tube 2. Thermometer 3. Stand with clamp 4. Thermometer 5. Stirrer 6. Beaker 7. Hot plate
Boiling point determination set up parts
A sealed capillary tube will serve as an indicator for determining the temperature, as when a rapid and continuous stream of air bubbles escape fromit, the vapour pressure of the liquid just exceeded the atmospheric pressure.
Explain why a sealed capillary tube is added instead of allowing the liquid sample to boil on its own.
1. INTERMOLECULAR FORCE 2. SURFACE AREA 3. PRESSURE
FACTORS THAT AFFECT BOILING POINT
INTERMOLECULAR FORCE SYMMETRY
FACTORS THAT AFFECT BOILING POINT
1. Stand With Clamp 2. Thermometer 3. Beaker 4. Capillary Tube 5. Stirrer 6 Hot Plate
Melting point determination Setup
•Distillation •Reflux •Thiele Tube
OTHER METHODS TO DETERMINE BOILING POINT
Strong IMF, Higher boiling point
Relation of intermolecular force and boiling point
Low Melting point, higher boiling point
Relation of melting point and boiling point
Higher pressure, higher boiling point
Relation of pressure and boiling point
Larger SA, higher boiling point
Relation of surface area and boiling point
The presence of impurities will make the sample heterogenous, and would therefore increase the disorder of the sample. The higher the disorder, the smaller the amount of energy is required to melt the sample, lowering its melting point.
How can the presence of impurities lower the melting point of organic compounds?
measure the melting points of all available pure compounds that range from the lowest melting point to the highest, and compare with the available melting point standard using a graphical method.
How can you calibrate a thermometer used for these types of determinations?
Note the temperature t1 when continuous stream of bubbles come out of the capillary tube. Stop heating and note the temperature t2 when the evolution of bubbles at the end of the capillary tube just stopped. The mean of t1 and t2 gives the boiling point of the liquid.
How would you determine the boiling point of an organic liquid using this method?
London Dispersion Force
Intermolecular force of Toluene
INTERMOLECULAR FORCE
The forces that hold atoms together within a molecule.