Acknowledgment
It gives me great pleasure to express my gratitude
towards our chemistry teacher Mrs. for her
guidance, support and encouragement throughout the
duration of the project. Without her motivation and
help the successful completion of this project would
not have been possible.
Student
Index
1. Acknowledgment
2. Objective Of The Project
3. Introduction
4. Theory
5. Experimental Procedure
● Experiment 1
● Experiment 2
● Experiment 3
6. Bibliography
Objective of the
Project
The objective of the project is comparison of rate of
evaporation of different liquids (acetone, benzene and
chloroform).
Also to demonstrate how the rate of evaporation
depends on following factors:
i) Surface Area of Liquid:
As surface area of liquid increases the rate of
evaporation of the liquid increases
ii) Temperature of Surroundings:
As the temperature of surroundings increases
randomness in molecules increases and the rate of
evaporation increases
iii) Air Current:
The rate of evaporation is higher in the presence of
air current.
Introduction
When a liquid is placed in an open vessel, it slowly
escapes into gaseous phase eventually leaving the
vessel empty. This phenomenon is known as
vaporization or evaporation. Evaporation of liquids
can be explained in the terms of kinetic molecular
model although there are strong molecular attractive
forces which hold molecules together. The molecules
having sufficient kinetic energy can escape into
gaseous 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
escapes into gaseous phase.
Evaporation causes cooling. This is due to the reason
that the molecules which undergo evaporation have
high kinetic energy therefore the kinetic energy of the
molecules which are left behind is less.
Since the remaining molecules which are left have
lower average kinetic energy. Therefore temperature
is kept constant the remaining liquid will have same
distribution of the molecular kinetic energy and high
molecular energy will kept one escaping from liquid
into gaseous phase of the liquid is taken in an open
vessel evaporation will continue until whole of the
liquid evaporates.
Theory
Factors affecting the rate of
evaporation:
(1) Nature of Liquids:
The magnitude of inter-molecular forces of attraction
in a liquid determines the speed of evaporation.
Weaker the inter-molecular forces of attraction,
larger are the extent of evaporation. In diethyl ether
rate of evaporation is greater than that of ethyl
alcohol.
(2) Temperature:
The rate of evaporation of liquids varies directly with
temperature. With the increase in the temperature,
fraction of molecules having sufficient kinetic energy
to escape out from the surface also increases. Thus
with the increase in temperature rate of evaporation
also increases.
(3) Surface Area:
Molecules that escape the surface of the liquids
constitute the evaporation. Therefore larger surface
area contributes accelerating evaporation.
(4) Composition of Environment:
The rate of evaporation of liquids depends upon the
flow of air currents above the surface of the liquid.
Air current flowing over the surface of the liquid took
away the molecules of the substance in vapour state
there by preventing condensation.
Experiment No. 1
Aim:
To compare the rates of evaporation of acetone,
benzene and chloroform.
Requirement:
Three same size Petri dishes of diameter 10 cm, 10
ml. pipettes, stop watch, acetone benzene and
chloroform.
Procedure:
1. Clean and dry all Petri dishes and identify them as
A, B and C.
2. Pipette out of 10 ml. acetone in Petri dish "A" with
stopper similarly pipette out of 10 ml. of benzene and
chloroform in each of Petri "B" and "C".
3. Remove the cover plates from all Petri dishes and
start the stop watch.
4. Let the Petri dishes remain exposed for 10 minute.
Now cover each of the petri dish and note the volume
of remaining material in them.
Observation:
Liquid Volume Volume
Petri
Taken Remaining Evaporated
dish
(V1) ml. (V2) ml V=V1–V2
Rate (V/T)
ml/s
8/600=
A
10
2
8
0.0133
7/600=
B
10
3
7
0.0116
6/600=
C
10
4
6
0.010
Results:
Rate of evaporation of Acetone is 0.0133 ml/s.
Rate of evaporation of Benzene is 0.0166 ml/s.
Rate of evaporation of Chloroform is 0.010 ml/s.
Experiment No. 2
Aim:
To study the effect of surface area on the rate of
evaporation of diethylether.
Requirement:
Three Petri dishes of diameter 2.5 cm., 5 cm., and 7.5
cm. with cover, 10 ml. of pipette and stop watch.
Procedure:
1. Clean and dry all Petri dishes and mark them as A,
B and C.
2. Pipette out of 10 ml. diethylether in each of the
Petri dishes A, B and C and cover them immediately.
3. Uncover all three Petri dishes and start the stop
watch.
4. Note the remaining volume after 10 min.
vaporization of diethyl ether from each Petri dish.
Observation:
Petri
Volume
Diameter
Remaining Evaporated
Dishes
Taken
of P.T.Ds.
Vol. (ml.) volume
Marked
(ml.)
A
2.5
10
4
6
B
5.0
10
2
8
C
7.5
10
0
10
Results:
The order of rate evaporation of acetone in three petri
dishes according to their diameter is
7.5 > 5.0 > 2.5 cm.
Experiment No.3
Aim:
To study the effect of temperature on the rate of
evaporation of acetone.
Requirement:
Two Petri dishes of 5 cm. diameter each stop watch,
10 ml. pipette, thermometer, and thermostat.
Procedure:
1. Wash and Clean, dry the Petri dishes and mark
them as A, B.
2. Pipette out of 10 ml. of acetone to each of Petri
dishes A and B and cover them.
3. Put one Petri dish at room temperature and to the
other heat for same time.
4. Note the reading.
Observation:
Petri
dishes
Marked
A
B
Volume Evaporated
Time Temperature
Taken
volume
(Sec.)
(K)
(ml.)
(ml.)
10
303
10
10
20
313
10
10
Results:
The order of evaporation of acetone in two Petri
dishes as given
Room Temperature < Heating.
Experiment No.4
Aim:
To study the effect of air current on the rate of
evaporation of acetone.
Requirement:
Two Petri dishes acetone.
Procedure:
1. Clean and dry the Petri dishes and mark them as A
and B.
2. Keep one dish where no air current and other under
a fast air current.
3. Note the reading.
Observation:
Petri
Time
dishes Conditions
(Sec.)
Marked
A
With fan
40
B
Without fan 50
volume
Evaporated
(ml.)
10
10
Results:
Rate of evaporation with fan
= 0.25 ml/sec
Rate of evaporation without fan = 0.20 ml/sec
Interpretation of
Result
i)
Comparison of rate of evaporation of
acetone, benzene and chloroform:
Rate of evaporation of acetone, benzene and
chloroform is in the order:
Chloroform < Benzene < Acetone
Hence the intermolecular forces are in the order:
Chloroform > Benzene > Acetone.
ii) Effect of area on rate of evaporation:
Larger the surface area more is evaporation, as it is
observed that acetone in petri dish with larger surface
area evaporates at a faster rate.
iii) Effect of temperature on rate of evaporation:
Observation clearly shows that the evaporation
increases with temperature. So an increase in
temperature favours the rate of evaporation.
iv) Effect of air current on rate of evaporation:
In the presence of fan the rate of evaporation is found
to be more, hence the rate of evaporation of liquid
increases with the increase in rate of flow of air
current.
Bibliography
i) en.wikipedia.org
ii) practicalchemistry.org
iii) google.com
iv)
N.C.E.R.T. Notebook For Chemistry, Class XII