Laboratory Experiment
pubs.acs.org/jchemeduc
Constructing a Simple Distillation Apparatus To Purify Seawater: A
High School Chemistry Experiment
Alandra Kahl,† Danita Heller,‡ and Kim Ogden*,†
†
Department of Chemical and Environmental Engineering, University of Arizona, Tucson, Arizona 85721, United States
Department of Chemistry, Ironwood Ridge High School, 2475 West Naranja Drive, Tucson, Arizona 85742, United States
‡
S Supporting Information
*
ABSTRACT: This experiment combines the chemistry of solution separation
via distillation with the engineering design process to motivate students in a
high school chemistry course. Students build upon their knowledge of phase
changes and solubility to complete a project related to chemical engineering by
desalinating a water sample similar to seawater. In general, students remove
very little of the salt, but the emphasis is on the creation of the system rather
than achievement of pure water. Resources for learning about distillation, an
exercise description, exercise worksheets, and assessment plans are provided in
the supporting information. This experiment fits well into a general chemistry
curriculum or an environmental science course. It takes a minimum of 5
standard (1 h) class periods, but can be expanded or downsized as is
appropriate. Student feedback was generally positive because the students
enjoyed solving a “real-world” problem.
KEYWORDS: High School/Introductory Chemistry, Environmental Chemistry, Laboratory Instruction, Physical Chemistry,
Hands-On Learning/Manipulatives, Inquiry-Based/Discovery Learning, Laboratory Equipment/Apparatus, Separation Science,
Water/Water Chemistry
D
and tenet 1 of the Science and Engineering in Practice of the
Next Generation Science Standards (NGSS).5 Also addressed
are cross-cutting concepts, such as energy, patterns, and scale of
the NGSS and strand 3, Science in Personal and Social
Perspective of the Arizona Science Standards. Finally, this
experiment is applicable to fulfillment of the Earth and Space
science portion of both the NGSS and Arizona Science
Standards.
istillation of ocean water for drinking water is motivated
by a continuous increase in population, which is causing a
shortage in the available freshwater supply. Approximately 2.3
billion people (41% of the world population) live in regions
with water shortages.1 As a result, solutions are needed, and
salt-water desalination has emerged as a key technology to
fulfilling the water demand. Desalination is a general term for
the process of removing salt from water to produce fresh water.
Fresh water is defined as containing less than 1000 mg/L of
salts or total dissolved solids (TDS).2 Thermal desalination
(distillation) has been used for hundreds of years to produce
fresh water, and large-scale municipal drinking water distillation
plants began to operate during the 1950s.3 In this exercise,
students research the distillation process and design their own
water purification systems.
This inquiry-based experiment was developed to aid student
understanding of phase changes and solution separation and to
spark an interest in chemical engineering by applying
fundamental concepts to a real-world problem. Student
exposure to the engineering design process before college has
shown to direct greater numbers of students to the engineering
disciplines, particularly underrepresented minorities and
females.4 Application of fundamental concepts to real-world
issues is an engagement tool that captures the interest of all and
is distinctly applicable to engineering and chemistry.
Specifically, application of this laboratory captures strand 1,
inquiry processes, of the Arizona Science Standards including
observation, scientific testing and analysis, and communication
© 2014 American Chemical Society and
Division of Chemical Education, Inc.
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OVERVIEW OF LABORATORY EXPERIMENT
This exercise centers on the fundamental concept of distillation,
which ties in closely with the ideas of phase changes and
solution separation. Distillation is a method of separating a
mixture based on volatility of components in a boiling liquid.
Distillation is a physical operation, not a chemical reaction,
making it ideal for an engineering design exercise in a chemistry
laboratory. In the experiment, students design and build an
engineered system to perform a distillation using the concept of
solution separation to “purify contaminated water” or remove
salt from water. The laboratory is conducted over five class
periods: the first period encompasses the lecture about water
purification and creation of student groups; the second period
continues the discussion about the components of a water
purification system and troubleshooting student designs; the
third and fourth periods include the setup of the water
Published: January 27, 2014
554
dx.doi.org/10.1021/ed400262v | J. Chem. Educ. 2014, 91, 554−556
Journal of Chemical Education
Laboratory Experiment
Figure 1. (A) Example of student distillation apparatus and (B) example recreated from the literature.7
Table 1. Example of a Student Data Table
Contaminated Water/g
Distilled Water/g
Salt Remaining/g
Container
Container + Water
Water
Container
Container + Water
Water
Container
Container + Salt
Salt
96.66
116.59
19.93
40.76
54.08
13.32
96.66
97.42
0.76
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purification system and performance, and the fifth period is for
the student presentations.
This is an engineering design process exercise, so students
should be familiar with steps of the engineering design process
prior to beginning. The engineering design process allows
students to focus on inquiry (strand 1 of the Arizona Science
Standards). Students meet the standards of concepts 1−4 in
their investigation, having used observation and prediction of
outcomes, scientific testing and investigation, evaluation of their
experimental design, and communication of their results to a
peer audience. Students are required to research distillation
processes for their water purification system and submit a
design based on their research to the instructor before
beginning construction. Student distillation apparatuses must
be approved for safety concerns by instructors prior to
construction and then again, before use. Students must also
design a data table to record measurements useful in proving a
successful separation of the solution with their apparatus.
Instructors provide students with a 4.0% NaCl solution (by
mass) to distill in their apparatus, and 0.1 M silver nitrate
solution to test the distillate upon culmination. In the presence
of salt, silver nitrate will generate a precipitate, visually
indicating to the student that their distillate is not free of the
salt.
STUDENT RESEARCH
Students are given two weeks to research the mechanics of
distillationwhat it is, how it is used in industry, and so
forthand design their distillation apparatus. Student research
is done outside of class time. In class during this period,
students are guided by the instructor as to the feasibility of their
apparatus (lecture available in Supporting Information). There
is also a video available for students to watch from online
resources.6 Scaffolding is provided in the form of in-class
discussions regarding the engineering design process, and
students are encouraged to self-reflect during the design
process. In class, students are encouraged to evaluate the design
of other groups along with the instructor to troubleshoot
designs. Students are supported by teacher and peer discussions
of the engineering design process aspects as they relate to their
design. Several iterations of the distillation apparatus are
expected as an aspect of monitoring student progress. Students
must show that they have revisited the engineering design
process before they can proceed to building and testing their
apparatus.
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MATERIALS AND PROCEDURE
Common chemistry glassware is used in this laboratory
experiment. At least two 250 mL Erlenmeyer flasks or beakers,
rubber stoppers, and one hot plate should be available per
student group. Thinking outside the common experimental
setup is especially encouraged in this laboratory, so other
materials (ice packs, plastic or metal tubing, etc.) should also be
available for student use. Instructors also need to purchase at
least 100 cm of glass tubing per group and a glasscutter for use.
Bunsen burners are provided to students along with relevant
instruction and demonstration of the proper way to bend glass
tubing.
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INTRODUCTORY LECTURE
Students are first introduced to the need for clean water
throughout the world, what contaminants exist in water, and
the difficulty in purifying water. Then phase changes and
solution separation are discussed, and pictures of distillation
apparatuses used by second-year engineering students are
shown (introductory notes are available in Supporting
Information). Finally, students form imaginary companies
consisting of groups of four individuals. The lecture by the
instructor and formation of the student groups is designed to
be done in the first class period. Students are provided a
handout describing the requirements of the experiment.
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DISTILLATION
Students are given one single, regular period to build the water
purification systems and one block period to do the experiment.
An example of a student distillation apparatus (version found
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dx.doi.org/10.1021/ed400262v | J. Chem. Educ. 2014, 91, 554−556
Journal of Chemical Education
Laboratory Experiment
The most cited criticism of the laboratory was the perceived
lack of instructor guidance. This can be attributed to limited
exposure of students to an inquiry-based laboratory process,
and the majority of students with this criticism also reported
that they liked the ability to be creative in the construction of
their distillation setup.
by students in literature and student rendering of their own
apparatus) and data table are provided in Figure 1 and Table 1,
respectively.
As expected, students were not able to fully separate the salt
from the water by their crude distillation apparatus. This was
confirmed by the addition of silver nitrate to the resulting
solution. It should be noted that based on the cleanliness of the
vessels used, a more dilute silver nitrate solution may be used to
avoid a positive result from residual chloride on glassware.
Generation of the precipitate silver chloride showed the
presence of remaining salt as a visual aid. Emphasis here was
not on the completeness of the distillation but on critical
evaluation of the system. Students were encouraged to think
about possible sources of contamination (clean glassware,
tubing, etc.), as well as to report their observations during
testing. For example, if students observed salt water bumping
over into the distillate, instructors emphasized this point during
discussion.
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CONCLUSIONS
To increase student exposure to the engineering design process,
it was our intent to develop an engaging laboratory experience
applying chemistry concepts to a real-world problem. Early
exposure of students to critical thinking and concept
application in chemistry will benefit them in college and
beyond. This laboratory exercise serves to expose students in
the engineering design process using their knowledge of
solution separation chemistry as a backbone. Students were
able to design an apparatus to distill water from salt water, build
and test their design, and critically evaluate the results. General
student response to this laboratory was positive, with the main
criticism of students being the perceived lack of guidance. In
response, instructors will attempt to provide more comprehensive feedback to students during the design and testing
process. Peer evaluation will also be used more, as students
respond positively and feel more involved in their learning if
they must provide feedback to others.
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HAZARDS AND SAFETY
Students are bending glass tubing to construct their distillation
apparatus, so care should be taken with glass and flame.
Students also insert glass tubing into rubber stoppers so care
should be taken. Proper technique is demonstrated to eliminate
injuries to the students. Hot plates are used to heat the salt
water, so care should be taken to avoid contact with the hot
surface. All proposed experimental set should be approved by
the instructor prior to construction to ensure they are not
closed systems. A closed system will result in pressure buildup
and be an explosion hazard. The chemicals used are safe (water
and salt).
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ASSOCIATED CONTENT
S Supporting Information
*
Student laboratory handout; lecture notes; student survey. This
material is available via the Internet at http://pubs.acs.org.
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PORTFOLIO AND PRESENTATIONS
Following testing of their distillation apparatus, student groups
collaborate on a simple design portfolio containing a 2−4 page
paper detailing (1) the focus of their company and objective,
(2) research relevant to the objective, (3) diagrams and data
tables from the construction and testing of their distillation
apparatus, (4) information regarding the efficiency and
limitations of their design, and (5) a discussion of why their
design should be used over others. Students work outside of
class to create the portfolio. Students then make a presentation
in class to their peers and the instructor that details the
construction and testing of their distillation apparatus.
AUTHOR INFORMATION
Corresponding Author
*E-mail: [email protected].
Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS
The authors would like to acknowledge support from the NSF
GK-12 program, grant no. 0947836.
REFERENCES
(1) Service, R. F. Desalination Freshens Up. Science 2006, 313
(5790), 1088−1090.
(2) U.S. Bureau of Reclamation Sandia National Laboratories.
Desalination and Water Purification RoadmapA Report of the
Executive Committee. DWPR Program Report #95; U.S. Department
of the Interior, Bureau of Reclamation and Sandia National
Laboratories: Denver, CO, 2003.
(3) Gleick, P. H. The World’s Water 2006−2007, The Biennial Report
on Freshwater Resources, 1st ed; Island Press: Chicago, IL, 2006.
(4) Sheppard, S.; Jenison, R. Examples of Freshman Design
Education. Int. J. Eng. Educ. 1997, 13 (4), 190−204.
(5) Arizona Department of Education, Standards Based Teaching and
Learning, “The Science Standard Articulated by Grade Level.” http://
www.azed.gov/standards-practices/science-standard/ (accessed Dec
2013).
(6) Distillation.” http://youtu.be/xxNfJLMNS4E (accessed Dec
2013).
(7) Ellervik, U.; Grudberg, H. A. Microscale Vacuum Distillation
Apparatus for Simple Separations. J. Chem. Educ. 1999, 76 (7), 986.
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STUDENT RESPONSE TO THE LABORATORY
EXERCISE
Following the exercise, students were instructed to complete a
brief survey to express their opinions of the experiment. Overall
student responses were favorable, and the majority of students
indicated that they found the laboratory to be highly
informative, beneficial, exciting, and enjoyable. Students
reported that “Application of the engineering design process
allowed us to creatively solve the problem. We really had to
analyze every step to build something that would work.” In
response to the question “The one or two things I most
enjoyed with this lab were”, a student wrote: “Actually seeing a
process which can be used in everyday life take place before
me.” Given the question “I felt this lab helped me understand
phase changes. Why or why not?” a student responded, “Yes,
because the research and hands on experiment allowed me to
fully understand the process that is involved.”
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