Class 9 Record Experiment 4

 EXPERIMENT – 4

Aim
To determine the melting point of ice and boiling point of water.

Theory

1. Melting Point: The temperature at which the solid changes into liquid at the atmospheric pressure is called melting point. For example, ice melts at 0°C to form water.

2. Boiling Point: The temperature at which the liquid boils and changes into gaseous state at the atmospheric pressure is called boiling point. For example, water boils at 100°C to form water vapour (at 76 cm pressure).

3. Latent Heat of Fusion: The heat energy absorbed during the melting of ice is stored in the water formed, this energy is called latent heat of fusion. The amount of heat energy that is required to change 1 kg of a solid into liquid at atmospheric pressure at its melting point is known as the latent heat of fusion.

4. Latent Heat of Vaporisation: The heat energy absorbed by water when it changed its phase to steam, this hidden heat is called latent heat of vaporisation.

Conditions Affecting Melting Point and Boiling Point

Materials Required
Two thermometers, (Celsius scale), boiling tube, a glass rod, two iron stands, a bunsen burner, wire gauze, beakers, tripod stand, distilled water, ice cubes prepared from distilled water.

Procedure
(A)To determine the boiling point of water.

1. Take 25-30 ml of water in a boiling tube and add few pumice stones to it.

2. Clamp the boiling tube on iron stand with two holed cork, in one hole fix the thermometer and in the other one fix the delivery tube.

3. Place the thermometer above the water in the flask as shown in the figure and record its temperature.

4. Place a burner under the boiling tube.

5. Read the temperature and record it in the given observation table till the water boils. Record the reading after the time interval of 1 minute.
   

Observation Table

Result

1. Boiling Point of water  is 100 °C.

2. Once the boiling point is attained the temperature reading on thermometer does not change for sometime.

(B)To determine the melting point of ice.

1. Take a beaker half-filled with the dry crushed ice obtained from distilled water.

2. Suspend a Celsius thermometer from the clamp stand such that the bulb of the thermometer is completely surrounded by ice.

3. Read the thermometer reading and record the temperature after every 1 minute till the ice melts and the thermometer reading remains stationary for 2 minutes.

4. Note the readings in the observation table.
   

Observation Table

Result

1. Melting point of ice is 0 °C.

2. Once the melting of ice begins the temperature remains constant for some time.

Precautions

1. Choose a better  quality thermometer whose graduated scale is clearly readable.

2. Record the temperature in whole numbers.

3. While reading the thermometer the eye level should be parallel with mercury level.

4. Dip only the bulb of thermometer into water/ice.

5. Thermometer should not touch the walls of beaker or boiling tube.