(A) to Determine the Melting Point of Ice

PRACTICAL EXPERIMENTS

EXPERIMENT NO.1

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

(a) To determine the melting point of ice.

MATERIALS REQUIRED: Beaker, wire gauze, tripod stand, burner, thermometer,

stirrer,icecubes,thermometer,clamp stand etc..

THEORY: The constant temperature at which a solid changes into a liquid is called melting point of the solid.

When a solid is heated, its molecules absorb heat energy and their kinetic energy increases. This results in rise of temperature of the solid. During melting, the temperature remains the same till the entire solid melts even though we continue to supply the heat.

The quantity of heat required to completely change 1 kg of ice into water without any change in temperature is known as latent heat of fusion of ice.

PROCEDURE: Take some ice cubes in a beaker and place it over a wire gauze kept over a tripod stand. Suspend a thermometer with the help of a clamp stand so that its bulb is in contact with the ice. Start heating the beaker on a low flame and note the temperature when the ice starts melting. Finally note the temperature when all the ice has been converted into water.

OBSERVATION: The temperature remains constant till the ice has completely melted i.e 0o Celsius.

RESULT: The melting point of ice is 00C .

PRECAUTIONS:

1. The bulb of the thermometer should be completely surrounded by ice.

2. Ice should be stirred regularly to keep a uniform temperature throughout.

3. Note temperature by keeping your eyes in line with the level of mercury.

(b) To determine the boiling point of water.

MATERIALS REQUIRED: Distilled water, boiling tube, rubber cork with two holes, delivery tube, clamp stand, thermometer, pumice stones etc.

THEORY: When heat energy is supplied to water, the particles start moving faster. At a certain temperature, a point is reached when the particles have enough energy to break free from the forces of attraction of each other. At this temperature the liquid starts changing into gas. The temperature at which a liquid starts boiling at the atmospheric pressure is known as its boiling point.

During the change of state from liquid to gas, the temperature of the system remains the same till the entire liquid is converted into vapours even though heat is continuously being supplied.

The amount of heat energy required to change 1 kg of liquid into vapours at atmospheric pressure at its boiling point is called latent heat of vapourisation.

PROCEDURE: Take some distilled water in a boiling tube and add few pieces of pumice stones to it. Fix a cork with two holes(one for thermometer and other for delivery tube) in the mouth of the boiling tube and clamp it with the stand. The thermometer should be introduced in such a way that the bulb of the thermometer is 3-4 cm above the surface of water. Heat the boiling tube and note the temperature when the boiling starts. Continue to heat till the temperature becomes constant and the water remains boiling. Note the constant temperature.

OBSERVATION: The temperature remains constant till all the water has been converted into vapour (i.e at 100oC.)

RESULT: The boiling point of water is 100oC

Plot a graph of Temperature vs Time (in minutes),

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PRECAUTIONS:

1. The bulb of the thermometer should be kept 3-4 cm above the surface of water

2.|Pieces of pumice stone should be added to water before heating to avoid bumping.

3. Heating of water should be done by rotating the flame.

4. Note temperature by keeping your eyes in line with the level of mercury.

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EXPERIMENT NO.2

Aim:To separate the components of a mixture of sand, common salt and ammonium chloride (or camphor) by sublimation.

Requirement: Common salt, sand and ammonium chloride, distilled water, china dish, funnel and tripod stand.

Principle:

• Constituents of a mixture can be separated by simple physical methods.
• Sublimation: It is the conversion of a solid directly into the vapour phase without changing to a liquid.
• Sublimation can be used to separate a volatile solid and a non-volatile solid in a mixture.
• The water-soluble solid/substance can be separated from non- water-soluble substance by filtration.

Experimental steps:

• Mix the salt, sand and ammonium chloride thoroughly to get a mixture.
• Take some amount of the mixture in a china dish; place it on a tripod stand for heating.
• Cover the china dish with an inverted funnel with some cotton plugged in its stem to prevent vapours escaping out.
• Continue heating for sometime until no more vapours of ammonium chloride are seen to be rising up.
• Remove the funnel carefully so that the ammonium chloride deposited does not fall.
• The mixture of sand and common salt remains in the china dish.

• Cool the contents of the china dish and dissolve in a minimum amount of water and filter.
• Sand remains as residue; the filtrate is concentrated by evaporation and left undisturbed for salt to crystallize out.

Conclusions:

• Ammonium chloride is a sublimable substance, which is first separated by subliming the mixture.
• Common salt readily dissolves in water and is separated from sand by dissolving in water and filtering the mixture.
• Residue obtained is only sand.
• Constituents of the given mixture could be separated by simple physical methods.

Precautions:

• While heating the mixture the china dish should be very stable on the wire gauze over the tripod stand.
• The funnel should not be very big otherwise vapours will escape out.
• The stem of the funnel should be plugged with cotton to prevent loss of ammonium chloride vapours.
• Water should not be added to the contents of the china dish unless it has cooled down.
• Ammonium chloride should be gently scraped off from the funnel once it has cooled to room temperature.