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Agra Public School,

Artoni, Agra.

TO STUDY THE RATE OF EVAPORATION OFDIFFERENT LIQUIDS

Submitted By:

Ashutosh Garg

XII B

Submitted To:

Mr. Manish Pathak

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I express my gratitude to my principal Mr. Manish Pathak who

is an incessant source of aspiration.

I am indebted to Shashi maam for her valuable guidance and

encouragement throughout the project work.

I also thank CBSE, for instructing me to complete an

investigatory project which has increased my knowledge about

chemistry and helped me to develop the feeling of

determination and hard work.

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Introduction 4.Factors effecting rate of evaporation 5.Objective of the project 6.Experiment 1 7.Experiment 2 8.Experiment 3 9.Experiment 4 10.Bibliography 11.

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When a liquid is placed in an open vessel, it slowly escapes into gas

phase, eventually leaving the vessel empty. This phenomenon is knownas vaporizationor evaporation.Evaporation of liquids can be explained

in terms of kinetic molecular model. Although there are strong

intermolecular attractive forces which hold molecules of a liquid together,

the molecules having sufficient kinetic energy can escape into gas phase if

such molecules happen to come near the surface. In a sample of liquid all

the molecules do not have same kinetic energy. There is a small fraction

of molecules which have enough kinetic energy to overcome the attractive

forces and escape into gas phase. Figure 1 shows typical energy

distribution for molecules of a liquid. If E corresponds to the minimumkinetic energy required to overcome attractive forces and escape, then

the shaded area in the graph represents the molecules which have

enough energy to overcome the attractive forces and can undergo

evaporation.

Kinetic Energy E

Figure 1.Energy distribution at different temperatures.

Evaporation causes cooling. This is due to the reason that the molecules

which undergo evaporation are high energy molecules, therefore the

kinetic energy of the molecules which left behind is less. Since the

remaining molecules have lower average kinetic energy therefore,

temperature must be lower. If the temperature is kept constant the

remaining liquid will have the same distribution of molecular kinetic

energies and the energy molecules will keep on escaping from the liquid

FractionofMolec

ules

Lower Temperature Higher Temperature

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into the gas phase. If the liquid is taken in an open vessel, evaporation

will continue until whole of the liquid evaporates.

Various factors that change the rate of evaporation are:

1. Nature of liquid. The magnitude of intermolecular forces ofattraction in the liquid determines to a large extent the speed of

evaporation; weaker are the intermolecular forces of attraction

larger is the extent of vaporization. For example, diethyl ether

evaporates more readily than propyl alcohol.

2. Temperature.The rate of evaporation varies directly withtemperature. Increasing the temperature also increases thefraction of molecules having sufficient kinetic energy to escape

from the surface. This results in increased rate of evaporation.

3. Surface of the liquid.Molecules that escape the surface ofliquid constitute evaporation. Therefore, larger surface area

contributes in accelerating evaporation.

4. The composition of the environment.The rate of evaporationdepends upon the flow of air currents over the surface of the

liquid. Air current flowing over the surface of the liquid carries

away the molecules of the substance in the vapour state, therebypreventing condensation and favouring evaporation.

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To compare the rates of evaporation of water, acetone and diethyl

ether.

Three weighing bottles; 10 ml pipettes, stop watch, weighing balance.

1. Clean and dry three weighing bottles. Identify them as A, B and C.2. Pipette out 10 ml of water to bottler A with stopper.3. Pipette out 10 ml of acetone to bottler B with stopper.4. Pipette out 10 ml of diethyl ether to bottler C with stopper.5. Weigh each of the bottles and record their weights.6. Remove the stoppers from all the three bottles and start the stop

watch.

7. Let the bottle remain exposed for 30 minutes. Now cover each ofthe bottle and weigh them again.

Weighingbottle mark

Liquidtaken

Initial massof bottle +

liquid

(W1)

Final massof bottle +liquid after30 minutes.

(W2)

Rate ofevaporation

W1 W2

30 m

A Water 10 g 9 g 0.03 g/minB Acetone 8 g 6 g 0.06 g/minC Diethyl ether 7 g 4 g 0.1 g/min

The rates of evaporation of the given three liquids is in the order

Diethyl ether > Acetone > Water

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To study the effect of surface area on the rate of evaporation of

diethyl ether.

Three petridishes of diameter 2.5 cm, 5 cm and 10 cm; with covers,

10 ml pipette and stop watch.

1. Clean and dry the petridishes and mark them as A, B and C.2. Pipette out 10 ml of diethyl ether in each of the petridishes A, B and

C and cover the immediately.

3. Uncover all the three petridishes simultaneously and start the stopwatch.

4. Note the time when diethyl ether evaporates completely from eachpetridish.

Petridishmark

Diameter ofpetridish

Time taken for completeevaporation.

A 2.5 cm 11 min 12 secB 5.0 cm 2 min 48 secC 10.0 cm 42 sec

It will be observed that maximum evaporation occurs in petridish with

largest diameter followed by smaller and then smallest petridish. It is,

therefore, concluded that rate of evaporation increases with increase in

surface area.

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To study the effect of temperature on the rate of evaporation of

acetone.

Two petridishes of same size, acetone, 10 ml pipette, thermometer,

thermostat and stop watch.

1. Wash, clean and dry the petridishes and mark them as A and B. 2. Pour 10 ml of acetone in each of the two petridishes and cover

them.

3. Maintain the temperature of thermostat at about 20o C higher thanroom temperature.

4. Remove cover of petridish A and allow the liquid in it to evaporateat room temperature.

5. Now uncover petridish B and immediately place it in thermostat setat 20o C higher than room temperature.

6. Start the stop watch and note the time taken for completeevaporation of acetone in two petridishes.

Petridishmark

Temperature Time taken for completeevaporation.

A 27o C 4 min 48 secB 47o C 1 min 9 sec

The observations clearly show that the rate of evaporation of acetone

increases with increase in temperature.

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