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Measurement of the Specific Latent Heat of Vaporisation of Water by the Bunsen Burner Method

Apparatus:

250ml beaker, stop-watch, thermometer, cloth, paper towels, top-pan balance, copper stirrer, bunsen burner, tripod, heat mat and gauze.

Procedure:

1. Measure the mass of the DRY 250ml beaker.

2. Fill the beaker with water so that it is approximately half full. Remeasure the mass and hence determine the mass of the water in the beaker.

3. Using a hot bunsen flame, measure the time taken for the water to be heated from 30oC to 80oC.

DO NOT TURN OFF THE BUNSEN WHEN YOU REACH 80 C AND Ensure that

(a) You continuously stir the water.

(b) You do not alter the position or setting of the bunsen burner.

4. Continue heating and restart the stop-watch once the water starts to boil (at around 100oC).

5. Boil the water for about 10 minutes, note the time taken boiling.

6. As soon as possible, remove the beaker and water from gauze and remeasure the mass and hence calculate the approximate mass of water boiled away. BE CAREFUL OF THE VERY HOT WATER!

Calculation of specific latent heat & discussion:

1. Calculate the heat energy supplied by the bunsen burner during stage 3 from

Heat energy supplied = Mass of water x SHC water x Temperature rise

Note

2. Calculate the power of the bunsen burner from:

Power of bunsen = Heat energy supplied / Time of heating (stage 3)

3. Calculate the heat supplied by the bunsen burner while boiling the water from:

Heat supplied (stage 5) = Power of bunsen x Time of heating (stage 5)

4. Calculate the specific latent heat of vaporisation of water from:

Heat supplied (stage 5) = Mass of water converted to steam x Specific latent heat

5. The accepted value of the specific latent heat of vaporisation of water is 2.1 MJ / kg.

Discuss why your answer is different from this.

6. A better method involves electrical heating.

In what ways is this method superior to using a bunsen burner?