To determine the boiling point of water - Class 9th Science Lab Work
Experiment - 13
Aim
To determine the boiling point of water.
Theory
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.
Procedure
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.
Precautions
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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