AIM
To determine the melting and freezing points of naphthalene
APPARATUS
Boiling tube, 250 cm beaker, stirring thermometer, tripod stand, retort stand and clamp, Bunsen burner, stopwatch, conical flask, wire gauze.
MATERIAL
Naphthalene, C H , tap water.
METHOD
A. HEATING OF NAPHTHALENE 1. Filled a boiling tube tube with naphthalene, naphthalene, C H to a depth of of 3 cm and put a thermometer into it. 2. Suspended the boiling tube in a beaker half-filled with water using a retort stand and a clamp. Ensure Ensure that the level of naphthalene, C H in the boiling boiling tube is below the level of water in the beaker. 3. Heated the water and stirred the naphthalene, naphthalene, C H slowly with the thermometer. thermometer. When the temperature of naphthalene, C H reached 60 C, started the stopwatch. 4. Recorded the temperature and and state of of naphthalene , C H at half-minute intervals until the temperature of of naphthalene, C H reached 90 C.
B. COOLING OF NAPHTHALENE 1.
Removed the boiling tube in activity A from the water bath. Dry the outer surface of the boiling tube and immediately putted it into a conical flask. Recorded the temperature and state state of naphthalene, C H at half-minute intervals intervals until the temperature drops to about 60 C.
2.
RESULT
A. HEATING OF NAPHTHALENE
Time (min)
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
6.5
7.0
Temperature ( C)
60
65
68
74
77
78
80
80
80
82
83
84
85
87
90
State
S
S
S
S
S
S+L
L
L
L
L
L
L
L
L
L
B. COOLING OF NAPHTHALENE Time (min)
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
6.5
7.0
Temperature ( C)
90
87
85
84
83
82
80
80
80
78
77
74
68
65
60
State
L
L
L
L
L
L
L
L
L
L+S
S
S
S
S
S
Inference
The flat section in each group indicates a change of state. The temperature remains constant as the heat energy is used to state the change of naphthalene.
Discussion
1. Why was a water bath used to heat the naphthalene, C H ? To ensure that naphthalene, C H is heated evently. 2. During the cooling of naphthalene, C H , explain why a) the boiling tube must be placed in a conical flask To ensure an even cooling. b) naphthalene, C H must be stirred continuously To avoid supercooling. 3. From the graph, deduce the melting and freezing point of naphthalene, C H . 80 C 4. Explain why the temperature remains constant for some time in both heating and cooling curves. Because the heat is used to change the state of naphthalene.
Conclusion
The melting and freezing point of naphthalene are the same.
