Ex 2

‫بسم ال الرحمن الرحيم‬ Name: ayedzahran Group: Day:

Experiment 2 "Determination of boiling and melting points of chemical compounds" I. Observations and results: Part A 1. Thermometer Calibration: Barometric pressure 640 tors Correct boiling point of water 97.3 C Thermometer reading in ice-water bath 1C Thermometer reading in boiling water bath 98 C Thermometer error: At 0C 1 At 100C 0.7 Plot the calibration graph of the thermometer using your experimental results 2. Unknown determination: Code number of unknown Observed boiling point Corrected boiling point Reference boiling point The unknown liquid is

B 57 C 56.2 C 56.1 C Acetone

Part B Observed melting point (rang)

(118-125)C

Reference melting point

122C

The recrystallized unknown substance is

Benzoic Acid

II. Answer the following questions: 1. Define: Boiling point of compound: The temperature at which the pressure of the vapor of the substance becomes equal to the prevailing external pressure on the surface.

Melting point of compound: The temperature at which the substance (crystals) change it's physical state from solid to liquid. 2. How will the following affect the boiling and melting points of a substance? a. A change in the barometric pressure Barometric pressure α boiling point, that's mean if barometric pressure increase the boiling point will increase and the opposite is correct. b. The presence of impurities in the substance The impurities in the substance will change the actual boiling or milting point for the substance for example if little of salt in water the milting point will be under zero siliceous degree so that in Europe they spray salt on ice-water to open the roads 3. How can you confirm that the identified unknown basing on boiling and melting points is actually that substance it is believed to be? When we do the steps of the experiment we have reading if this reading as or nearly of the reference point in the table of boiling and melting points that's mean we have the same substance.