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Friday 23 July 2021

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.

1st. 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 3/4th of wax melted.
  • Stop heating and note the temperature of wax when it starts freezing.
  • Find average of both temperatures.

2nd. 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 3/4th of wax melted.
  • Stop heating and note the temperature of wax when it starts freezing.
  • Find average of both temperatures.

OBSERVATIONS:
INITIAL TEMPERATUREFINAL TEMPERATUREMEAN TEMPERATURE
Temperature at which wax starts meltingTemperature at which liquid wax starts freezingMelting 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


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