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

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4 comments:

  1. I read your post which is very good ,we will wait for next post
    Tripod Stands

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  2. 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