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
C
Corrected
56.2 C
Reference
56.1 C
The
unknown
Acetone
Part B
Observed
B
57
boiling
point
boiling
point
liquid
melting
point
is
(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.