Pages

▼

Monday, 5 January 2015

2.1.2 Laboratory Activity : Determining the melting point of naphthalene

Laboratory Activity 2.1.2:
Determining the melting point of naphthalene
Aim: Determining the melting point of naphthalene
Material:
» Naphthalene
» Water 		Apparatus:
» Boiling tube
» Retort stand and clamp
» Tripod stand
» Wire gauze
» Thermometer(0 – 110 ºC)
» 250 ml conical flask
» Stop watch
» Bunsen burner
» Test tube holder


Procedures:

► The animation below shows the procedures of the heating and cooling of the naphthalene.

► (A) Heating of naphthalene
1. 3 spatulas full of naphthalene powder are placed in a boiling tube.
2. A 500 ml beaker is filled with water until it is about full. It is then placed on a tripod stand.
3. The boiling tube containing naphthalene is clamped in the beaker of water, making sure the naphthalene powder is below the water level of the water bath.
4. The water bath is heated until it reaches a temperature of about 90 ºC. The water is then heated with a low flame.
5. A stop watch is started and the temperature of the naphthalene is recorded at 30 second intervals until the temperature reaches . The naphthalene is stirred continuously during the experiment.
6. The results are recorded in a table.

► (B) Cooling of naphthalene
1. The boiling tube containing the molten naphthalene is removed from the hot water bath using a test tube holder.
2. It is immediately transferred into a conical flask to be cooled slowly.
3. The stop watch is started and the temperature of the naphthalene is recorded at 30 second intervals until it drops to about 60 ºC. The naphthalene is stirred continuously during the experiment.
4. The results are recorded in a table.
Results:

► (A) Heating of naphthalene
Time (s) 0 30 60 90 120 150 180 210
Temperature (ºC)

► (B) Cooling of naphthalene
Time (s) 0 30 60 90 120 150 180 210
Temperature (ºC)
Analysis:

► A graph of temperature against time is plotted for the heating of naphthalene.


► A graph of temperature against time is plotted for the cooling of naphthalene.
Discussion:

► In the heating of naphthalene, a water bath is used instead of direct heating.
○ This is to ensure that an even heating process is carried out.

► In the cooling of naphthalene, the boiling tube containing the liquid naphthalene is cooled inside a conical flask.
○ This is to ensure that an even cooling process is carried out.

► Stirring the naphthalene continuously also ensures even heating or cooling.

► A water bath is suitable in this experiment because the melting point of naphthalene is below 100 ºC.

► If the melting point of the substances is above 100 ºC, the water bath will have to be replaced by an oil bath.

► Besides naphthalene, the other substance that is suitable for heating by the water bath is acetamide.

Conclusion:

► The melting point and the freezing point of naphthalene is 80 ºC

⇲ For exercise(objective and subjective), download for free on Android OS.

15 comments:

  1. Unknown15 January 2017 at 02:57

    Tq

    ReplyDelete
  2. Unknown15 January 2017 at 17:52

    Tq

    ReplyDelete
  3. Unknown23 July 2017 at 09:38

    the need for an HCD. An ECCMID attendee noted that this approach has also been initiated at one or more hospitals in Europe. See the image below for the full poster (sorry for image quality, it’s my own iPhone pic!). solar air conditioner

    ReplyDelete
  4. Unknown20 March 2019 at 15:55

    why is paraffin oil preferred to water in this experiment

    ReplyDelete
    Replies
    1. Vision Technics9 July 2019 at 10:17

      Paraffin oil has a higher boiling point than water (above 100°C). Therefore, it would not evaporate by the time the temperature of both napthalene and paraffin oil reaches above 100°C

      Delete
  5. Unknown19 July 2019 at 20:26

    Can i know what are the precautional steps can be taken?

    ReplyDelete
    Replies
    1. Unknown20 November 2019 at 21:15

      heating process
      stir the naphthalene to ensure even heating

      cooling process
      stir the naphthalene to prevent supercooling

      Delete
  6. Unknown20 January 2020 at 05:51

    Why need water bath

    ReplyDelete
  7. History Of Football12 February 2020 at 07:24

    A water bath is laboratory equipment made from a container filled with heated water.it is used to incubate samples in water at a constant temperature over a long period of time

    ReplyDelete
  8. Unknown17 February 2020 at 00:39

    Why is naphthalene not heated directly using the Bunsen burner?????????

    ReplyDelete
  9. Unknown25 February 2020 at 08:19

    What are some of the assumptions in the experiment

    ReplyDelete
  10. Unknown11 March 2020 at 10:08

    What is the trend for the heating and the cooling of the naphthalene

    ReplyDelete
  11. Unknown9 May 2020 at 17:52

    During heating, why does the water bath level higher than the naphthalene??

    ReplyDelete
  12. Unknown14 April 2022 at 20:42

    Whys naphthalene stirred continuously during cooling process

    ReplyDelete