Determination Of Melting Point Of An Organic Compound

Chemical compounds which contain carbon is known as an organic compound. Study of manufacturing and synthesis of chemical compounds is known as organic chemistry. The temperature at which the chemical compound changes its state from solid to liquid is said to be the melting point of the compound. Let us learn to determine the melting point of organic compounds like naphthalene and benzoic acid.

Aim:

To determine the melting point of organic compounds like Naphthalene and benzoic acid.

Materials Required:

Naphthalene, benzoic acid, the aluminum block, stand with clamp, capillary tube, tripod, thermometer, and kerosene burner

Experimental setup:

Procedure to determine the melting point of Naphthalene:

  1. Take a capillary tube and close its one end by heating the end in the flame for 2-3 minutes while continuously rotating it.
  2. Take naphthalene on a tile and crush it into a fine powder.
  3. As shown in the figure below, firmly hold the closed end of the capillary tube between your finger and thumb.
  4. Dip the open end of the capillary tube in the finely powdered naphthalene.
  5. Gently tap the capillary tube on the table to fill the compound in the capillary tube to about a length of 1–2 cm.

Capillary Tube

Figure (a)

  1. With the help of a thread, attach the capillary tube to a thermometer as shown in the figure below.

Capillary Tube with Thermometer

Figure (b)

  1. Place the capillary tube in the groove of the aluminum block.
  2. Double check that the capillary tube holding the naphthalene is in the middle of the groove.
  3. Place the Aluminium block on a tripod stand above the kerosene burner and start heating the block with the burner.
  4. Keep continuous watch of the temperature and note the temperature as soon as the substance starts to melt.
  5. Make note of the temperature (t1) as soon as the compound begins to melt.
  6. Make note of the temperature (t2) as soon as the compound is melted completely.
  7. The average of the two readings gives the correct melting point of the substance.

Procedure to determine the melting point of Benzoic Acid:

  1. Take Benzoic acid on a tile and crush it into a fine powder.
  2. Take a capillary tube and by heating one end close the end of the tube.
  3. hold the closed end of the capillary tube between your finger and thumb as shown in figure (a) above.
  4. Dip the open end of the capillary tube in the finely powdered Benzoic acid.
  5. Fill the compound in the capillary tube to about a length of 1–2 cm by gently tapping the capillary.
  6. Attach the thermometer to a capillary tube using a thread as shown in the figure (b) above.
  7. Place the capillary tube in the groove of the aluminum block.
  8. Check if the capillary tube holding the benzoic acid is exactly in the middle of the groove.
  9. Place the Aluminium block on a tripod stand above the kerosene burner and start heating the block with the burner.
  10. Keep continuous watch of the temperature and note the temperature as soon as the substance starts to melt.
  11. Note the temperature (t1) as the substance begins to melt.
  12. Make a note of the temperature (t2) when the substance has completely melted.
  13. The average temperature of the substance is determined.

Precautions to be taken during the experiment:

  • Make sure the sample of Naphthalene and Benzoic acid are dry and powdered.
  • Keep the capillary tube and the thermometer at a similar level.
  • Tightly pack the powder into the capillary tube without any air gaps.

Observation

Temperature observation of Naphthalene

Temperature t1

Temperature t2

The melting point of Naphthalene (t1 + t2 / 2 )

Temperature observation of Benzoic acid

Temperature t1

Temperature t2

The melting point of Benzoic acid (t1 + t2 / 2 )

Frequently Asked Questions on Determination Of Melting Point Of An Organic Compound

What is the temperature at which a substance changes from solid state to liquid state called ?

Melting point

Why benzoic acid or Naphthalene needs to be crushed ?

Since by nature Naphthalene and benzoic acid are crystalline in nature, to get the fine power these compounds need to be crushed.

How is the melting point of the compound determined ?

The average temperature readings give the correct melting point of the substance.

What is a sharp melting point ?

If the melting point of the substance is within a range of 1-degree Celsius.

Due to the high melting point which element is used as filaments in the light bulb ?

Tungsten

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