Chemistry Practicals For Class IX (Science Group) - Experiment No. 3: To determine the boiling point of a given liquid.

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EXPERIMENT NO.3:

TO DETERMINE THE BOILING POINT Of A GIVEN LIQUID

APPARATUS:

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

CHEMICALS:

• Ethyl Alcohol (carbon tetra-chloride and paraffin liquid or any given liquid)
• Water

THEORY:
Temperature A which the vapour pressure of liquid becomes equal to the atmosphere pressure is called boiling point.
The boiling point is a physical property of a substance. It can be defined in terms of the vapour pressure of the solvent. It is the temperature at which the vapour pressure of the liquid Of solvent in a solution is equal to external pressure (i.e. atmospheric pressure). This means liquids can boil at almost any temperature if the external pressure is adjusted. When the pressure on a liquid is increased the boiling point goes up, and if the pressure on a liquid is reduced so it lowers the boiling point. Boiling point is also a characteristic constant, a pure liquid boils at a higher temperature whether the liquid contains a non-volatile or volatile impurities.

1^st. METHOD:

• Seal a small capillary glass tube at one end.
• Take a small quantity (2 ml) of ethyl alcohol in a small test tube.
• Insert the sealed capillary tube upside down into the small test tube, inside the ethyl alcohol.
• Tie the small test tube with a thermometer in such a way that its lower encl remain near the bulb.
• Suspend the thermometer on a clamp.
• Take it beaker half filled with water and place it over a wire gauze which is placed over a tripod stand.
• Lower the thermometer along with the small test tube into the water without touching the wall base by adjusting the clamp on the stand.
• Fix the clamp.
• Now slowly heat the beaker with a Bunsen burner or spirit lamp with constant stirring the water.
• When bubbles come out rapidly from the lower end of capillary tube, the temperature on thermometer is noted.
• Stop heating by removing the burner or spirit lamp.

2^nd. METHOD:

• Seal a small capillary glass tube at one end.
• Take a small quantity (2 ml.) of ethyl alcohol in a small test tube.
• Insert the sealed capillary tube upside down into the test tube, inside the ethyl alcohol.
• Clamp the test tube with iron stand and put it into the beaker which contains water and placed on a tripod stand such that ethyl alcohol remain In water.
• Now clamp a thermometer with an iron stand and dip it into the ethyl alcohol in such a way that its bulb remain in ethyl alcohol.
• Now slowly heat the beaker with a Bunsen burner or spirit lamp with constant stirring the water.
• When bubbles come out rapidly from the lower end of capillary tube, the temperature on thermometer is noted.
• Stop heating by removing the burner or spirit lamp.

OBSERVATIONS:
Boiling point of ethyl alcohol is 78 °C.

RESULT:
Boiling point of given sample of ethyl alcohol (C₂H₅OH) is 78 °C.

PRECAUTIONS:

• Water should be heated gently.
• Stirring should be constant.
• Bulb of thermometer 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 boiling point determination.
• The graduated side of thermometer should face you.

Note: Result may be vary depending on the purification of ethyl alcohol.
Special Thanks to Sir Sajjad Akber Chandio