SOTM LAB: C6
I.
TEACHER NOTES & GUIDELINES
TITLE OF LAB: Determining the Evaporation Rates of Liquids
DEVELOPERS OF LAB: Stephannie Costello JD 866, Brian Timm JD586, Craig Browne JD708,
Maureen Clark JD710, Jim Clinton JD865, SOTM staff
OVERVIEW OF LAB
DESCRIPTION
Evaporation rates of acetone, water and ethanol will be observed using lab top computers and
temperature probes. A post-lab component will then follow to uncover reasons why there are
differences in evaporation rates. The students will then design experiments to explore different
variables that would influence evaporation rates and how this could have a real-world application in
developing a product to cool the inside of a car on a hot summer’s day.
CURRICULUM CONSIDERATIONS
This lab could be used in a unit pertaining to:
Hydrogen bonding
Covalent bonding
Polar/Non-polar molecules
Phase changes
Electronegativities and the use of electronegativities in determining bond types
Intermolecular forces
Temperature
Kinetic energy
SAFETY CONSIDERATIONS
Wear safety goggles at ALL times
Alcohol and acetone are extremely flammable.
Acetone fumes are toxic
BACKGROUND INFORMATION
A. SCIENTIFIC VIEWPOINT
Evaporation is a cooling process that occurs when high-energy molecules at the surface of a liquid
break away as a vapor and take energy with them. Water molecules are held together by strong
hydrogen bonds caused by the polar bonds between the oxygen and hydrogen atoms. These forces
slow down the rate of evaporation, which minimizes the loss of heat energy. Ethanol exhibits some
hydrogen bonding also, but only at the end containing the OH group. The rest of the molecule has
nonpolar covalent bonds between carbon and hydrogen atoms. Weak attractive forces occur
between nonpolar molecules when the electrons move temporarily and create a temporary dipole
shift (Van der Waal forces) and have a slight attraction for the electrons in a neighboring molecule.
Although the acetone contains the same elements as ethanol, there are no direct bonds between
oxygen and hydrogen. Therefore, no hydrogen bonding occurs. There are some weaker dipoledipole forces that hold the acetone molecules together but not with as much strength as the bonds in
ethanol or water.
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B. COMMON MISCONCEPTIONS
Misconception
1, Heating and cooling make molecules change,
not just move faster and slower.
2. Temperature is a measure of heat and cold
inside an object.
3. The temperature of an object is a measure of the
amount of heat it contains.
4. Evaporation and boiling are chemical changes:
e.g. hydrogen is separated from the oxygen and
that is what the bubbles are.
5. No concept of intermolecular forces affecting
the rate of evaporation. They only think speed of
molecules influences evaporation.
6-When a substance evaporates, it vanishes.
Concept
Heating and cooling are physical changes only,
affecting the potential or kinetic energy of
molecules.
Temperature is a measure of the AVERAGE kinetic
energy of a sample’s particles.
Heat is measured in calories or joules, not degrees.
Heat is the TOTAL kinetic energy of a sample’s
particles.
Evaporation and boiling are phase changes, not
chemical changes.
Van der Waals forces, hydrogen bonding and dipole
forces influence rate of evaporation.
Matter can not be created or destroyed.
OBJECTIVES
This lab can serve as a review of the kinetic theory and its relation to evaporation and the
thermodynamics of evaporation.
Students should be able to explain how hydrogen bonding and other intermolecular forces of
attraction effect the rate of evaporation.
Students will be able to use structural models and electronegativity values to explain how bond types
influence the evaporation of a liquid.
Students will construct a control/variable experiment and make predictions of its outcome.
This lab will encourage cooperative and active learning among students to explore entrepreneurial
opportunities
EQUIPMENT/MATERIALS
PROVIDED BY SOTM
Laptop computer
Science Workshop interface
Temperature sensor
PROVIDED LOCALLY
Distilled water
Acetone
Ethanol
3 test tubes
Test tube rack
Paper towel
Goggles and lab apron
Scissors
Metric ruler
Stoppers
Parafilm
Class set of small pump spray bottles
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ADVANCE PREPARATION:
Procedure for Pasco setup:
1. Connect the Science Workshop interface to the computer.
2. Connect the DIN plug of the temperature sensor into the Analog Channel A of the interface.
(You do not need to calibrate the temperature probe.)
3. Turn on the interface
4. Open and start computer
5. Open Science Workshop by double clicking on the Science Workshop icon.
6. On the computer interface screen, click and drag the analog plug icon to channel A on the
interface, where the temperature probe has been plugged.
7. From the sensor list shown, scroll to and select the basic temperature sensor.
8. At the interface screen, click and drag the Graph icon and drop it on the temperature probe icon.
9. Do the same for the table icon.
10. Arrange the various windows by clicking and dragging on the title bar at the top of each
window. Move the windows until all are visible. Make the windows smaller or larger as needed
by clicking and dragging on the edge of the window.
II. PRE-LAB EXERCISE TO ELICIT STUDENTS’ PRIOR
KNOWLEDGE AND MISCONCEPTIONS
Students are given the following questionnaire to assess their misconceptions:
What causes a liquid to evaporate?
When a liquid evaporates, where does it go?
What’s the difference between evaporation and boiling?
How can you make a liquid evaporate faster or slower?
Do all liquids evaporate at the same rate? If not, why not?
When a substance evaporates, does it cool down or warm up?
DISCUSSION OF PRECONCEPTIONS
Correlate the answers from the pre-lab exercise to determine which misconceptions the student has.
III. EXPLORATION OF SCIENTIFIC PRINCIPLE &
INTRODUCTION OF EXPERIMENTAL PROTOCOL
PROBLEM:
Determine the evaporation rates of water, acetone, and ethanol.
EXPERIMENT AND TECHNICAL OPERATION OF EQUIPMENT
1. Obtain 3 mL of acetone. Place it in a labeled and stoppered test tube (parafilm may be used in
place of the stoppers). Place the test tube in a test tube rack.
2. Repeat step 1 with distilled water and ethanol.
3. Cut 3 pieces of l cm x 3 cm rectangles of paper towel.
4. Wrap the end of the temperature sensor with 1 piece of the cut paper towel so that it is totally
covered with no metal showing. Attach the paper to the probe by wrapping a strip of parafilm
around the section of paper NOT covering the temperature probe.
5, To check if the equipment is working correctly, click on the MON button on the computer
screen. When you see data points on the graph display, click on the STOP button.
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6. Remove the cork or parafilm from the acetone test tube and dip the paper towel covered end of
the sensor into the liquid. Remove the sensor and click the REC “button”. Allow the liquid to
evaporate for 2 minutes (120 sec.) Do not blow on the sensor.
7. Observe the graph being produced. At the end of 120 seconds, click on the STOP button."
8. Remove the paper towel from the sensor and dispose of it.
9. Repeat steps 4 - 8 for both water and ethanol, separately. All 3 curves produced should be on
the same graph. To display all the curves, click on DATA in the graph window and be sure
there is a check mark in front of all sets of data.
10. Save your data and graphs on a disk in drive A as EVAP1. Your teacher will print your graphs
for you.
Teacher Notes:
It is obvious from the sample data shown on Fig 1 on the graph that there is a significant difference in the
rates of evaporation of the 3 liquids. By drawing the best-fit straight lines for the falling portion of each
curve, it is possible to make a relative comparison between these rates. The expression for the rate of
evaporation of each liquid is:
acetone:
y = 0.2x + 24
ethanol:
y = 0.07x + 24
water:
y = 0.03x + 24
Acetone evaporates at the fastest rate and
the water at the slowest rate. An eventual
increase in temperature for the acetone and
ethanol trials may occur if all of the liquid
has completely evaporated and the probe
begins to warm up to room temperature.
Any rise in temperature will be less
noticeable if excess liquid is placed on the
piece of paper towel.
Related Web sites:
www.sos-tek.com
www.mistngo.com
www.kesmist.com/nozzle4.htm
www.mistymate.com
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POST-LAB QUESTIONS:
1. Draw a best-fit line along the falling portion of the data points for each curve. Calculate the slope of
each line. What does the slope of each line represent?
2. Rank the liquids from slowest to fastest evaporation rates.
3. Use electronegativities and structural formulas to determine the bond type and polarity of the water,
acetone and ethanol molecules. Which molecule is the most polar? Why?
4. Describe the types of attractive forces that hold water, acetone and ethanol molecules together.
5. Explain why different liquids evaporate at different rates.
6. What prevents liquids from evaporating?
7. Examine the predictions you made about the rates of evaporation for water, acetone and ethanol prior
to the lab. Were they accurate? Why or why not?
8. What did you learn from this lab that you previously did not know or did not understand?
9. Why do some window cleaners leave spots? If you were a chemical engineer for the cleaning
corporation how would you solve this problem?
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IV. ELABORATION OF SCIENTIFIC PRINCIPLE:
INQUIRY-BASED STUDENT INVESTIGATION
Teacher Notes: (Questions that can be used to start students in their inquiry assignments)
Does the temperature of the room affect evaporation rate?
Does the humidity of the room affect evaporation rate?
Does the airflow of the room affect evaporation rate?
What are the evaporation rates of some common household products?
Why do mist fans work?
What does the experiment with alcohol and acetone tell you about how nail polish and alcohol swabs
work?
Why do muscle creams make you feel hot and cold at the same time?
Can you create a liquid that when sprayed will lower the temperature of a closed car passenger
compartment in the summer?
PROBLEM:
Option 1 - Students are to create a solution that when used in a pump spray bottle can lower the
temperature of a closed car passenger compartment in the summer.
Option 2 - Students are to investigate the cooling rates of various household products.
Option 3 - Students are to investigate factors that affect the cooling rate of a specific liquid.
HYPOTHESIS OR PREDICTION
What type of solution will work best at lowering the temperature of a passenger compartment?
What household materials evaporate the fastest and why?
What factors affect the rate of evaporation of a known material?
EXPERIMENTAL DESIGN
Option 1 - Students are to design a solution and a method for testing their solution. Before the student
can proceed to the next step, they must check with the teacher
Option 2 - Students will collect data runs on various household products and explore and explain the
intermolecular forces that support their data.
Option 3 - Students are to investigate what factors will affect the rate of cooling for a known material.
Checkpoint (Teacher checks students’ experimental design for feasibility.)
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RUBRIC FOR ASSESSMENT OF STUDENT INQUIRY LAB
Student’s Name___________________________
Student activity
Students have proposed a question.
Students have proposed a hypothesis.
Students have stated reason for predicted outcome.
Students have created procedure
Students have considered safety and viability.
Students have identified controls.
Students have identified variables.
Students have created a material list.
Students have successfully run procedure.
Students have recorded data correctly.
Students have completed calculations.
Students have listed % error and sources of error.
Students have proposed ways to improve the
procedure.
Have students tested their hypothesis?
Are the student’s conclusions consistent with their
data?
Are student’s data, calculations and outcome
logical and consistent with known scientific
concepts?
What new questions have arisen during this lab?
Date of Completion
Teachers Initials
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Student’s Name ______________________
PLAN FOR DATA COLLECTION & ANALYSIS
(Teacher’s note: Questions you may want to use to guide students through planning their inquiry)
What question do you want to answer?
What is your hypothesis?
What do you think will be your outcome?
Are you only testing one variable?
How are you keeping all other conditions unchanged?
Will you be able to get all of the materials that you will need?
Checkpoint (Teacher checks students’ plan for feasibility.)
CONDUCTING THE EXPERIMENT
(Teacher’s note: Questions you may want to use to guide students through conducting their inquiry)
Do you have all of the materials needed to conduct your experiment?
Are you following acceptable safety protocol?
Are you following your own procedure or have you needed to make revisions?
Have you recorded you data correctly and with the correct units?
Checkpoint (Teacher monitors students’ investigations in progress.
ANALYSIS OF DATA
(Teacher’s note: Questions you may want to use to guide students through analysis of their inquiry)
What calculations will you need to reach your conclusion?
Are you calculations in the correct units?
Checkpoint (Teacher checks students’ analysis.)
DISCUSSION OF RESULTS
1. COMPARE
Does your calculations parallel what you had predicted? Explain.
Were there any sources of error in you procedure? Explain.
Does your data support or dispute your hypothesis? Explain.
2. PERSUADE
Can you use your conclusion to convince a non-science student that your conclusion is correct?
Explain.
3. RELATE
How can you relate your findings to the world outside the lab room?
IV. EVALUATION
POST-LAB SURVEY OF STUDENTS’ CONCEPTIONS
Have students retake the Pre-Lab Exercise. Compare pre-lab and post-lab responses.
TRADITIONAL
Using a standard test to evaluated student’s conceptual knowledge.
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ALTERNATIVE
Option 1: Have students write and perform an Infomercial for their product. They must be able to
express correct concepts using scientific language and terminology. The informercial must
use data collected during their experiments to compare their product to other possible
products on the market.
Option 2:
Have students create a magazine add on a poster board for their product. They must be able to
express correct concepts using scientific language and terminology. The informercial must
use data collected during their experiments to compare their product to other possible
products on the market.
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Name _______________________________
Evaporation Lab
Student Self-Evaluation
1. Describe the purpose of this lab project.
2. What new learning occurred for you as a result of doing this project?
3. If you could continue working on this project to make it better or more authentic, what would you
change and why?
4. What science ideas or understandings did you learn from doing this project?
5. What kinds of skills (e.g., use of computer, teamwork, etc.) did you use in this project that you will be
able to use in other areas of your life?
This material is based upon work supported by the National Science Foundation under Grant No. ESI 9618936. Any opinions, findings, and
conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National
Science Foundation.
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Infomercial Rubric
Excellent
4 pts.
Good
3 pts.
Fair
2 pts
Poor
1pt.
Unsat
0 pts.
Concept was
usually
apparent
used some
terms
accurately
Concept was
lacking most of
the time
very few terms
used accurately
sometimes
used
incorrect or
inappropriate
science
terminology
well prepared prepared and
not
and made no
made a few
completely
mechanical
mechanical
prepared and
errors: the
errors that did
made
overall
not interfere
mechanical
presentation
with
errors that
was effective
effectiveness of did not did
the presentation not interfere
with the
presentation
presented
missing 1 piece missing 2
detailed
of selling
pieces of
information on information
selling
cost, ordering
information
procedure,
why you need
this product,
highlights of
products over
others in the
market
most of the
time used
inappropriate
or incorrect
science
terminology
not prepared
and made
mechanical
errors; some
interfered with
presentation
no evidence of
concept
incorporated
used terms
inaccurately/did
not use terms at
all
all terminology
was incorrect
Concept of
Evaporative
Cooling
Understanding
Concepts
Concept was
evident
throughout
all terms used
accurately
Concept was
apparent
Overall
Vocabulary
used specific,
appropriate
science
terminology
often used
specific,
appropriate
science
terminology
Mechanics
Selling
Information
all but 1 or2
terms used
accurately
missing 3
pieces of
selling
information
not prepared and
made
mechanical
errors; many
interfered with
the presentation
missing 4 pieces
of selling
information
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