To determine the boiling point of water - Class 9th Science Lab Work

Experiment - 13

To determine the boiling point of water.

The temperature at which a liquid changes into its vapour state is known as its boiling point. Once a liquid attains its boiling point, the temperature remains same until all the liquid changes into its vapour.

Materials Required
Round bottom flask (250 mL), a double bored cork, beaker (100 mL), thermometer (-10ºC − 110ºC), stop-watch (or a stop-clock), spirit lamp(or gas burner), tripod stand with wire gauze, spring balance, a glass tube, a polythene bag, laboratory stand, water, crushed ice, and thread.

Step 1: The range and the least count of the thermometer is noted.
Step 2: About 150 mL water in the round bottom flask is taken and its mouth is closed with a two-holded stopper. Thermometer is fixed through one of the holes in the cork and a glass tube through the other [Fig. 1]. Make sure that the bulb of thermometer hangs in air and is not in contact with water in the flask.
Step 3:Wire gauze is placed on a tripod stand and the flask is kept over it. Water is heated with a spirit lamp or a gas burner.
Step 4: Stop-watch is switched on (or stop-clock) and the reading of the thermometer is noted after fixed intervals of time, say 2 minutes. Once the temperature rises above 80ºC, the time interval to read the thermometer should be reduced, say to one minute.
Step 5: The thermometer readings are recorded for 4-5 minutes even after the water in the flask begins to boil.

Observation and Calculations

Sl. No. Temp. at which water starts boiling in ºC (t1) Water continues to boil in ºC (t2) Boiling point of water
(t1+t2)/2 (in ºC)
1 100 100 (100+100)/2=100ºC
2 99 101 (99+101)/2 = 100ºC

Results and Discussion
The boiling point of water is 100ºC.

1. Thermometer in the flask should be fixed in a manner that its bulb does not touch the water surface in the flask.
2. Recording of temperature and time should be done simultaneously.

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