STUDY OF RATE OF EVAPORATION OF DIFFERENT LIQUIDS A Project Report
Submi ubm i tted by
I n partial partial f ulf il lment lment of of the
CBSE GRADE XI IN
Chemistry AT
AECS MAGNOLIA MAARUTI PUBLIC SCHOOL Arekere, Off Bannerghatta Road, Bangalore- 560076
2013-2014
CERTIFICATE This is to certify that Rohin Gopalakrishnan of Grade XI, AECS Magnolia Maaruti Public School, Bangalore with the Register Number A33 has satisfactorily completed the project in Chemistry on The study of rate of evaporation of different liquids in partial fulfillment of the requirements as prescribed by CBSE in the year 2013-14.
Signature of the Teacher in Charge
Signature of the Principal
Signature of the Candidate
Signature of the External Examiner
ACKNOWLEDGEMENT I warmly acknowledge the continuous encouragement and timely suggestions offered by our dear Principal Dr.Seema Goel. I extend my hearty thanks for giving me the opportunity to make use of the facilities available in the campus to carry out the project successfully.
I am highly indebted to Mrs. Kunhilaxmi K. and Mrs. Neelam A. for the constant supervision, providing necessary information and supporting in completion of the project. I would like to express my gratitude towards them for their kind co-operation and encouragement.
Finally, I extend my gratefulness to one and all who are directly or indirectly involved in the successful completion of this project work.
Signature of the candidate
INDEX
Introduction
1
Objective, Scope and Application
2
Theory
3 – 4
Experiment 1
5-6
Experiment 1
7-8
Experiment 1
9 - 10
Experiment 1
11 - 12
Conclusion and Result
13
Bibliography
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Introduction This project is about studying and observing the rate of evaporation is the process whereby atoms or molecules in a liquid state (or solid state if the substance sublimes) gain sufficient energy to enter the gaseous state. Evaporation is the process whereby atoms or molecules in a liquid state (or solid state if the substance sublimes) gain sufficient energy to enter the gaseous state. The thermal motion of a molecule must be sufficient to overcome the surface tension of the liquid in order for it to evaporate, that is, its kinetic energy must exceed the work function of cohesion at the surface. Evaporation therefore proceeds more quickly at higher temperature and in liquids with lower surface tension. Since only a small proportion of the molecules are located near the surface and are moving in the proper direction to escape at any given instant, the rate of evaporation is limited. Also, as the faster-moving molecules escape, the remaining molecules have lower average kinetic energy, and the temperature of the liquid thus decreases. If the evaporation takes place in a closed vessel, the escaping molecules accumulate as a vapor above the liquid. Many of the molecules return to the liquid, with returning molecules becoming more frequent as the density and pressure of the vapor increases. When the process of escape and return reaches equilibrium, the vapor is said to be "saturated," and no further change in either vapor pressure and density or liquid temperature will occur.
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Objective of project In this project, we shall investigate various factors such as nature of liquid, surface of liquid, temperature and effect of air currents and find their correlation with the rate of evaporation of different liquids by four simple experiments using various liquids.
Scope and Limitations Through these experiments we can do a broad study of solvents. An idea of characteristics and physical properties can be assumed. Through these experiments, one can improve existent systems that use evaporation, for example, drying of clothes in houses. We can also understand the science behind ‘matkas’, which applies a good deal of scientific knowledge. The main limitation lies in the fact that all environmental factors cannot be manually controlled, and I must have sufficient room for error. I hope to increase my knowledge and broaden the scope of the topic as much as possible, with the course of the experiments I perform.
Applications When clothes are hung on a laundry line, even though the ambient temperature is below the boiling point of water, water evaporates. This is accelerated by factors such as low humidity, heat (from the sun), and wind. In a clothes dryer, hot air is blown through the clothes, allowing water to evaporate very rapidly. A hair dryer too works on the same principle.
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Theory Evaporation is the process whereby atoms or molecules in a liquid state (or solid state if the substance sublimes) gain sufficient energy to enter the gaseous state. The thermal motion of a molecule must be sufficient to overcome the surface tension of the liquid in order for it to evaporate, that is, its kinetic energy must exceed the work function of cohesion at the surface. Evaporation therefore proceeds more quickly at higher temperature and in liquids with lower surface tension. Since only a small proportion of the molecules are located near the surface and are moving in the proper direction to escape at any given instant, the rate of evaporation is limited. Also, as the faster-moving molecules escape, the remaining molecules have lower average kinetic energy, and the temperature of the liquid thus decreases. If the evaporation takes place in a closed vessel, the escaping molecules accumulate as a vapor above the liquid. Many of the molecules return to the liquid, with returning molecules becoming more frequent as the density and pressure of the vapor increases. When the process of escape and return reaches equilibrium, the vapor is said to be “saturated,” and no further change in either vapor pressure and density or liquid temperature will occur.
Factors influencing rate of evaporation 1. Concentration of the substance evaporating in the air - if the air already has a high concentration of the substance evaporating, then the given substance will evaporate more slowly 2. Concentration of other substances in the air - if the air is already saturated with other substances, it can have a lower capacity forth substance evaporating. 3. Temperature of the substance - if the substance is hotter, then evaporation will be faster
4. Flow rate of air - this is in part related to the concentration points above. If fresh air is moving over the substance all the time, then the concentration of the substance in the air is less likely to go up with time, 3
thus encouraging faster evaporation. In addition, molecules in motion have more energy than those at rest, and so the stronger the flow of air, the greater the evaporating power of the air molecules. 5. Inter-molecular forces - the stronger the forces keeping the molecules together in the liquid or solid state the more energy that must be input in order to evaporate them.
6. Surface area and 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. Molecules that escape the surface of the liquids constitute the evaporation. Therefore larger surface area contributes accelerating evaporation. 7. Nature of Liquids - the magnitude of inter-molecular forces of attraction in 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. 8. 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 vapor state thereby preventing condensation. 9. Density - the higher the density, the slower a liquid evaporates. In the US, the National Weather Service measures the actual rate of evaporation from a standardized "pan" open water surface outdoors, at various locations nationwide. Others do likewise around the world. The US data is collected and compiled into an annual evaporation map. The measurements range from under 30 to overthe120 inches (3,000 mm) per year 10. Pressure - in an area of less pressure, evaporation happens faster because there is less exertion on the surface keeping the molecules from launching themselves.
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EXPERIMENT – 1 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 10ml of water to bottle A with stopper. 3. Pipette out 10 ml of acetone and diethyl ether in such of bottles B and C respectively. 4. Weigh each of the bottles and record their weights. 5. Remove the stoppers from all the three bottles and start the stop watch. 6. Let the bottles remain exposed for 30 minutes. Now cover each of the bottle and weigh them again.
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Liquid Taken
Initial Volume(V)
Time taken to Evaporate (T)
Rate (V/T)
Chloroform
10
1750
0.0057
10
555
0.0181
10
1025
0.009
10
850
0.0011
Diethyl Ether Petroleum Ether Methanol
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EXPERIMENT - 2 To study the effect of surface area on the rate of evaporation of diethyl ether.
Three petridishes of diameters 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 10ml of diethyl ether in each of the petridishes A, B and C and cover them immediately. 3. Uncover all the three petridishes simultaneously and start the stop watch. 4. Note the time when diethyl ether evaporates completely from each petridish.
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Petridish mark (ml)
Diameter of Time taken for complete petridish (cm) evaporation (s)
3
2.5
135
3
5.0
220
3
7.5
245
8
EXPERIMENT - 3 To study the effect temperature on rate of evaporation of acetone.
Two petridishes of 5 cm diameter each, stop watch, 10 ml pipette, thermometer, thermostat.
1. Wash, clean and dry the petridishes and mark them as A and B. 2. Pipette out 10ml of acetone to each of the petridishes A and B and cover them. 3. Maintain the temperature of thermostat at about 20 C higher than room temperature. 4. Remove cover of petridish A and allow the liquid in it to evaporate at room temperature. 5. Now uncover petridish B and immediately place it in thermostat set at 20 C higher than room temperature. 6. Start the stop watch and note the time taken for complete evaporation of acetone in the two petridishes. 9
Petridish mark (ml) 10 10
Temperature (°c) Increasing to 50° C Room Temperature
10
Time taken for complete evaporation 1550 sec 1550 sec
EXPERIMENT - 4 To study the effect of air current on rate of evaporation.
Two petridishes and acetone.
1. Pour 10 ml of acetone in each of the two petridishes of the same size. 2. Keep one dish in a place where there is no fan and the other under a fan. Start the stop watch and note and note the time taken for complete evaporation of acetone in both the dishes.
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Petridish mark
Conditions
Time taken for complete evaporation (s)
A
With Fan
545
B
Without Fan
1928
Without Fan
With Fan
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CONCLUSION AND RESULTS
The rates of evaporation of the given liquids o Diethyl Ether > Methanol > Petroleum Ether > Chloroform The liquids having weaker intermolecular forces has greater rate of evaporation
Maximum evaporation occurs in petridish with larger diameter followed by the smaller and the smallest petridish. It is therefore concluded that rate of evaporation increases with increase in surface area.
Evaporation of Petroleum Ether increases with increase in temperature. The rate of evaporation increases with increase temperature because there is an increase in kinetic energy of molecules.
The liquid under the fan evaporates faster. This shows that the increase in the rate of evaporation increases with the flow of air current on the surface of the liquid.
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Bibliography
www.google.com www.gobookee.org www.howstuffworks.com Chemistry Lab Manual CBSE Text book
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