Activity 2.2:
Aim: To determine the melting point and freezing point of naphthalene, C10H8.
Materials: Naphthalene, C10H8 and water
Apparatus: Boiling tube, 250 cm3 beaker, thermometer, tripod stand, retort stand with clamp, Bunsen burner, stopwatch, conical flask, wire gauze and spatula
Procedure:
1. Fill up one third of a boiling tube with naphthalene, C10H8.
2. Place a thermometer in the boiling tube.
3. Pour water into a beaker until it is half filled.
4. Immerse the boiling tube into the beaker as shown in Figure 2.4. Ensure the level of naphthalene, C10H8 in the boiling tube is below the level of water in the beaker.
5. Heat water and stir the naphthalene, C10H8 slowly using the thermometer. When the temperature of the napthalene, C10H8 reaches 60 °C, start the stopwatch.
6. Record the temperature and state of matter of naphthalene, C10H8 at 30 seconds intervals until the temperature reaches 90 °C.
7. Remove the boiling tube from the water bath. Dry the outer surface of the boiling tube and put it into a conical flask as shown in Figure 2.5.
8. Stir the naphthalene, C10H8 continuously.
9. Record the temperature and state of matter of naphthalene, C10H8 at 30 seconds intervals until the temperature decreases to 60 °C.
10. Record your observations.
Interpreting data:
1. Plot a graph of temperature against time for the following:
(a) Heating of naphthalene, C10H8
(b) Cooling of naphthalene, C10H8
2. On the graphs, label the states of matter of naphthalene, C10H8 whether solid, liquid or both.
3. Determine the melting point and freezing point of naphthalene, C10H8 from the graphs plotted.
Discussion:
1. During the heating of naphthalene, C10H8:
(a) Why is naphthalene, C10H8 not heated directly using the Bunsen burner?
(b) Why is a water bath used?
2. During the cooling of naphthalene, C10H8:
(a) Why is the boiling tube put into a conical flask?
(b) Why is naphthalene, C10H8 stirred continuously?
(c) Predict what would happen if naphthalene, C10H8 is not stirred continuously.
3. Explain why the temperature becomes constant when melting and freezing of naphthalene, C10H8 take place.
Answer:
Discussion:
1. (a) Naphthalene, C10H8 is a flammable substance.
(b) Water bath method helps to distribute heat evenly. This ensures even heating.
2. (a) To ensure even cooling
(b) To distribute heat evenly
(c) Supercooling will happen
3. During melting, heat energy that is absorbed by the naphthalene particles C10H8 is used to overcome attraction force between the particles so that the solid changes to liquid.
During cooling, heat energy that is released to the surroundings is balanced by the heat energy released when particles attract each other to form a solid.
Aim: To determine the melting point and freezing point of naphthalene, C10H8.
Materials: Naphthalene, C10H8 and water
Apparatus: Boiling tube, 250 cm3 beaker, thermometer, tripod stand, retort stand with clamp, Bunsen burner, stopwatch, conical flask, wire gauze and spatula
Procedure:
1. Fill up one third of a boiling tube with naphthalene, C10H8.
2. Place a thermometer in the boiling tube.
3. Pour water into a beaker until it is half filled.
4. Immerse the boiling tube into the beaker as shown in Figure 2.4. Ensure the level of naphthalene, C10H8 in the boiling tube is below the level of water in the beaker.
5. Heat water and stir the naphthalene, C10H8 slowly using the thermometer. When the temperature of the napthalene, C10H8 reaches 60 °C, start the stopwatch.
6. Record the temperature and state of matter of naphthalene, C10H8 at 30 seconds intervals until the temperature reaches 90 °C.
7. Remove the boiling tube from the water bath. Dry the outer surface of the boiling tube and put it into a conical flask as shown in Figure 2.5.
8. Stir the naphthalene, C10H8 continuously.
9. Record the temperature and state of matter of naphthalene, C10H8 at 30 seconds intervals until the temperature decreases to 60 °C.
10. Record your observations.
Interpreting data:
1. Plot a graph of temperature against time for the following:
(a) Heating of naphthalene, C10H8
(b) Cooling of naphthalene, C10H8
2. On the graphs, label the states of matter of naphthalene, C10H8 whether solid, liquid or both.
3. Determine the melting point and freezing point of naphthalene, C10H8 from the graphs plotted.
Discussion:
1. During the heating of naphthalene, C10H8:
(a) Why is naphthalene, C10H8 not heated directly using the Bunsen burner?
(b) Why is a water bath used?
2. During the cooling of naphthalene, C10H8:
(a) Why is the boiling tube put into a conical flask?
(b) Why is naphthalene, C10H8 stirred continuously?
(c) Predict what would happen if naphthalene, C10H8 is not stirred continuously.
3. Explain why the temperature becomes constant when melting and freezing of naphthalene, C10H8 take place.
Answer:
Discussion:
1. (a) Naphthalene, C10H8 is a flammable substance.
(b) Water bath method helps to distribute heat evenly. This ensures even heating.
2. (a) To ensure even cooling
(b) To distribute heat evenly
(c) Supercooling will happen
3. During melting, heat energy that is absorbed by the naphthalene particles C10H8 is used to overcome attraction force between the particles so that the solid changes to liquid.
During cooling, heat energy that is released to the surroundings is balanced by the heat energy released when particles attract each other to form a solid.