Chemistry Practicals For Class IX (Science Group) - Experiment No. 2: To determine the melting point of a given solid

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EXPERIMENT 2

TO DETERMINE THE MELTING POINT OF A GIVEN SOLID.

APPARATUS:

• Thermometer
• Beaker
• Test tube
• Rubber band
• Stirrer
• Tripod stand
• Iron stand
• Wire gauze
• Spirit lamp (Bunsen burner)

CHEMICALS:

• Candle wax (using urea, stearic acid and acetamide Or any other solid)
• Water

THEORY:
The temperature at which a solid becomes a liquid at standard atmospheric Pressure is called melting point.

OR

The temperature at which a solid and its liquid are in equilibrium, at any fixed pressure is called melting point.

OR

The melting point of a solid is the temperature at which it changes state from solid to liquid.
The melting is a physical property of a substance. It is the temperature at which the crystals of a pure substance are in equilibrium with the liquid phase at atmospheric pressure.
A pure solid will generally melt sharply because the forces of attraction between its particles are the same. An impure solid melts at a lower temperature and over a wider range. Thus, a solid's melting point is useful not only as an aid in identification but also as an indication of purity.

1^st. METHOD:

• Fill one quarter of test tube with candle wax.
• Tie it to a thermometer in such a way that the wax portion is close to the thermometer bulb. Suspend the thermometer onto the clamp.
• Take some water in a beaker.
• Put the beaker on a wire gauze, over a tripod stand.
• Lower the thermometer along with the test tube by adjusting the clamp.
• Fix the clamp on iron stand.
• The bulb of thermometer should be dipped in the water.
• Heat the beaker slowly by means of Bunsen burner with constant stirring the water with stirrer.
• Note the temperature when ³/₄^th of wax melted.
• Stop heating and note the temperature of wax when it starts freezing.
• Find average of both temperatures.

2^nd. METHOD:

• Fill one quarter of test tube with candle wax.
• Clamp the test tube with iron stand and put it into the beaker which is already placed on a tripod stand and filled with water such that candle wax remains in water.
• Now clamp a thermometer with an iron stand and dip it into the candle wax in such a way that its bulb remains in candle wax.
• Heat the beaker slowly by means of Bunsen burner with constant stirring the water with stirrer.
• Note the temperature when ³/₄^th of wax melted.
• Stop heating and note the temperature of wax when it starts freezing.
• Find average of both temperatures.

OBSERVATIONS:

INITIAL TEMPERATURE	FINAL TEMPERATURE	MEAN TEMPERATURE
Temperature at which wax starts melting	Temperature at which liquid wax starts freezing	Melting point t = t1 + t2/2
_____ °C	_____ °C	_____ °C

RESULT:
Melting point of given candle wax is ___________ °C.

NOTE: Repeat the experiment by using urea, stearic acid and acetamide or any other solid and record their melting points.

PRECAUTION:

• Water should be heated gently.
• Stirring should be constant.
• Thermometer bulb should not touch the walls and base of the beaker.
• Too much or too little sample can be a cause of error.
• Adjust flame size so that the temperature rises no more than 2-3 degree per minute.
• A sample is only used once for melting point determination.
• The graduated side of thermometer should face you.

Special Thanks to Sir Sajjad Akber Chandio