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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 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
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