Laboratory Experiment
pubs.acs.org/jchemeduc
Soybean Oil: Powering a High School Investigation of Biodiesel
Paul De La Rosa,† Katherine A. Azurin,‡ and Michael F. Z. Page*,‡
†
Northview High School, Covina, California 91722, United States
Chemistry Department, California State Polytechnic University, Pomona, Pomona, California 91768, United States
‡
S Supporting Information
*
ABSTRACT: This laboratory investigation challenges students to synthesize, analyze, and
compare viable alternative fuels to Diesel No. 2 using a renewable resource, as well as
readily available reagents and supplies. During the experiment, students synthesized
biodiesel from soybean oil in an average percent yield of 83.8 ± 6.3%. They then prepared
fuel samples consisting of commercial Diesel No. 2, B100 (100% biodiesel), and blended
B20 (80:20 Diesel No. 2 to biodiesel). During analysis, the students determined that the
fuels contained an average energy value of 3626.2 ± 622.0 kJ/kg (B100), 3675.6 ± 723.7
kJ/kg (B20), and 4349.5 ± 1019.2 kJ/kg (Diesel No. 2). The experiment requires three 50
min lab periods and reinforces crosscutting educational science standards. It can enrich
science discussions in either a high school or an introductory university chemistry class
regarding sustainability and stewardship.
KEYWORDS: High School/Introductory Chemistry, Interdisciplinary/Multidisciplinary, Laboratory Instruction,
Public Understanding/Outreach, Hands-On Learning/Manipulatives, Applications of Chemistry, Calorimetry/Thermodynamics,
Fatty Acids, Plant Chemistry
O
relevant to solving global problems.11 For example, approximately 94% of the U.S. transportation energy is supplied by
petroleum-based fuel12 and approximately 50 billion gallons of
diesel fuel is consumed annually.13 Alternatively, biodiesel has
fuel properties similar to petrodiesel14 and can be used directly
in a diesel engine. Biodiesel improves lubricity and reduces
toxic emissions during combustion.15 Overall, the United States
has the fourth greatest biodiesel production potential in the
world.16 Collectively, the nation has the ability to grow enough
soybeans to meet food demands and address the need for
alternative energy sources.4 If only 5% of the imported oil was
replaced with biodiesel, it would account for the amount of oil
imported from Iraq.17
Facets of fuel technology and environmental stewardship
have been thematic in a number of articles that have appeared
in this Journal.4,9,18−25 Recently, high school students have been
challenged to synthesize biodiesel from oils extracted from algal
lipids,26 and others have utilized a fifty-gallon reactor to convert
waste vegetable oil as part of collaborations between their
science and agricultural departments.27 The interdisciplinary
nature of biotechnology has also extended to high school
students being able to produce bioethanol from facial tissues.28
Biodiesel serves as a broad teaching platform to allow
introductory university students to understand the scientific,
quality control, and analytical testing aspects of the fuel
industry. The properties of biodiesel, such as heat value, vapor
pressure, enthalpy, entropy, and Gibbs free energy, are relevant
to thermodynamic discussions within general chemistry
ver the past two decades, scientists and policy makers
have been working together to define and address
complex issues of sustainability.1 This topic has been woven
into the fabric of modernized chemistry curriculum striving to
equip students with principles of ethics2 and stewardship,3
while building their critical-thinking and data-analysis skills.4
Recently, the National Research Council, the National Science
Teachers Association, the American Association for the
Advancement of Science, and Achieve have worked with
twenty-six U.S. states to enhance science education through the
development of the Next Generation Science Standards
(NGSS).5,6 This lab is a practical application of the NGGS
Disciplinary Core Idea of Energy.7 The synthesis and analysis of
biodiesel provides an opportunity to implement the following
practices in a K−12 science classroom:5 (i) planning and
carrying out investigations, (ii) analyzing and interpreting data,
(iii) using mathematics and computational thinking, (iv)
constructing explanations, and (v) engaging in argument from
evidence. Furthermore, energy is a NGGS crosscutting theme8
that bridges disciplinary boundaries in a student’s K−12
academic maturation. This experiment serves to enhance a
student’s understanding of energy by exploring bonding in fatty
acid methyl esters (FAME), calculating the heat value and
energy density of a renewable fuel source, and engaging in
technical laboratory experiences.
By incorporating green methodologies9,10 in various levels of
the curriculum, future scientists will be better prepared to
integrate sustainability in future innovations. These scientific
dialogues during a student’s development should naturally lead
to a wider understanding and demonstrate that chemistry is
© XXXX American Chemical Society and
Division of Chemical Education, Inc.
A
dx.doi.org/10.1021/ed400436z | J. Chem. Educ. XXXX, XXX, XXX−XXX
Journal of Chemical Education
Laboratory Experiment
courses.29,30 In addition to synthesis, these topics are developed
in greater detail in organic, physical, and analytical university
courses, which typically have been the first opportunity for
university students to characterize FAMEs as alternative
fuels.31−42
separatory funnel or heavy-duty conical vial, and the layers
were separated overnight.
Fuel Blending and Energy Density Analysis. During the
second lab session, after the biodiesel and aqueous layers were
allowed to separate, the fuel was collected and the mass
recorded. The students then mixed approximately half of their
synthesized biodiesel with Diesel No. 2 in an 80:20 ratio by
volume (B20). Following the blending, students measured the
energy density of each fuel sample: B100, B20, and Diesel No.
2. The groups filled ethanol fuel lamps with approximately 5
mL of each fuel and measured how long a known volume of
each sample burned.26
Heat Value Analysis. In the third lab session, the students
calculated the energy content of the various fuels. A
calorimetric apparatus was constructed using a clean empty
soda can supported by a ring stand and containing a
thermometer. Each group added 50 mL of deionized water to
the aluminum can and recorded the initial temperature of the
water. As a cotton ball holding a precise mass of each fuel
sample was burned and heated the system, the students
monitored changes in the water temperature.44
Diesel Engine Combustion. Following a classroom
discussion of data precision and accuracy, the combined
student samples (either B100 or B20) that adhered to
classroom quality assurance specifications were combined and
used to power an industrial diesel engine generator (Yanmar
LV100 V).45 For instance, the fuel samples chosen to be
combusted in the engine demonstrated consistency in the
acquired energy density and heat values by the selected student
groups. No student data was collected during the engine
combustion demonstration. This experience was included to
further strengthen a lasting impression that biotechnology can
address global concerns. Furthermore, any small diesel engine
can be substituted and used during this portion of the lesson.
■
EXPERIMENTAL OVERVIEW
A series of lab experiments were developed in which high
school students addressed the question, “Is domestic soybean
oil a viable alternative biofuel?” These lab experiments were
piloted in two local high school chemistry classes (containing
25−30 students) and used as an enrichment experience to
several groups of 12−24 high school students visiting the
university as part of outreach events and summer programs.
After a short introduction of covalent bonding in various
fuels (petroleum and alternative sources), students were
encouraged to research biodiesel synthesis procedures from
reputable Web sites and journal articles. In the first lab session,
students gained technical experience by synthesizing FAMEs
from soybean oil. This synthesis featured an innocuous catalyst,
employed minimal solvents, and bypassed a fuel-drying step. In
the second lab session, students completed two tasks. First,
they prepared the fuel samples consisting of commercial Diesel
No. 2, B100 (100% biodiesel), and blended B20 (80:20 Diesel
No. 2 to biodiesel). Second, the students collected energy
density data of each sample. In the third lab session, the
students collected heat value data of each fuel sample.
Following the completion of the laboratories, the students
analyzed and interpreted data regarding side-by-side comparisons of the various fuels. As an enrichment experience
following the data analysis discussion, the student fuel samples
can be used to power an industrial diesel generator engine.
The structure of the experiment presented herein required
three 50 min class periods (with two additional sections used as
a prelab discussion and data analysis period). Overall, this
lesson challenged students to address global concerns using
evidence and scientific reasoning. The analytical experiments
reinforced the thermodynamic topics and energy calculations
containing specific heat values used in high school and general
chemistry courses. This lab series enriched discussions of
energy in either high school or introductory university
chemistry classes through the synthesis and characterization
of B100 and B20 as an alternative fuel to petroleum-based
diesel.
■
HAZARDS
Potassium carbonate is an irritant and should be handled while
wearing gloves and safety glasses. Skin exposed to methanol,
glacial acetic acid, soybean oil, or the resulting FAME should be
flushed with water and washed with soap. Both fatty acids are
combustible liquids with a closed cup flash point of
approximately 282 °C. Diesel No. 2 is a flammable liquid
with a closed cup flash point of 38 °C. The waste generated in
this experiment should be disposed of following typical
laboratory protocols. Individual high school sites should also
adhere to specific site, district, and state protocols. Some
general guidelines regarding noncommercial biodiesel waste
procedures are available from the U.S. Environmental
Protection Agency.46
Procedure
Chemicals. Soybean oil (CAS 8001-22-7), anhydrous
K2CO3 (CAS number: 548-087), methanol (CAS number 6756-1), and glacial acetic acid (CAS number 64-19-7) were
purchased from Fischer Scientific and used without further
purification. Commercial grade Diesel No. 2 (CAS number
68476-30-2) was purchased from a local fueling station and
stored in a sealed carrying vessel prior to usage.
Transesterification.43 After reviewing the bonding within
triglycerides and petroleum-based fuels during the prelab, the
students were placed in groups of at least four to work
collaboratively. In the first lab session, 20.0 mL of soybean oil
(assumed to have an average molar mass of 880 g/mol),
anhydrous K2CO3 (6% of the mass of oil), and anhydrous
methanol (6 mmol per mmol of oil) were added to a 100 mL
round-bottom flask. After refluxing for 25 min, a dilute solution
(17.5 mL) of acetic acid (1 M) was added to neutralize the
reaction. The mixture was stirred and transferred to a
■
RESULTS
The transesterification of soybean oil to biodiesel took place in
25 min by reacting potassium carbonate in a small excess of
refluxing methanol.43 Neutralizing the reaction mixture with
dilute acetic acid allowed the mixture to separate into two
layers. This procedure resulted in students obtaining the
desired alternative fuel in an average percent yield of 83.8 ±
6.3%. The shortened reaction time, minimal use of solvents,
and the incorporation of an innocuous catalyst allowed this
synthesis to be implemented in the high school curriculum
where lab class sections meet for as little as 50 min at a time.
B
dx.doi.org/10.1021/ed400436z | J. Chem. Educ. XXXX, XXX, XXX−XXX
Journal of Chemical Education
Laboratory Experiment
current biodiesel communications and offers a tangible example
of a lab series that meets NGGS educational standards by
illuminating how the fuel sector can be reformed in a
sustainable manner utilizing chemistry and energy transfer in
a real-world manner.
During the energy density analysis, the students determined
that each fuel sample burned for an average time of 351 ± 3 s/
mL (B100) and 386 ± 16 s/mL (B20). The B100 sample
displayed an average decrease of 9.09% when compared with
the energy density of the B20 mixture. By adding 5 mL of each
sample to a fuel lamp, students recorded the total time the fuel
burned using a cotton wick. Commercial Diesel No. 2 burned
beyond the allocated classroom period time, that is, values
greater than 600 s/mL. During the heat value analysis portion
of the experiment, the students determined that the three fuel
samples contained an average of 3626.2 ± 622.0 kJ/kg (B100),
3675.6 ± 723.7 kJ/kg (B20), and 4349.5 ± 1019.2 kJ/kg
(Diesel No. 2). By adding a precise mass of each fuel sample to
individual cotton balls, the students recorded the temperature
change of water in a calorimeter as the fuel samples were
burned. The change in temperature was converted to energy
using qv = C × dT × m (where qv = heat, C = specific heat, dT =
change in temperature, and m = the mass of water in the
calorimeter). Overall, the students concluded that B100
displayed an average heat value decrease of 16.6% and B20
displayed an average decrease of 15.5% when compared to
Diesel No. 2, respectively.
■
ASSOCIATED CONTENT
S Supporting Information
*
Instructions for students, student handouts, and instructor
notes. TThis material is available via the Internet at http://
pubs.acs.org.
■
AUTHOR INFORMATION
Corresponding Author
*E-mail: [email protected].
Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS
We acknowledge the dedication of Merlyn Conwell and
Vanessa Ramirez and their students for piloting this
investigation in their high school chemistry classrooms. Also
we acknowledge the generous support of the John T. Lyle
Center Regenerative Studies Faculty Fellowship Program at Cal
Poly Pomona for supporting the growth and expansion of
biodiesel in chemical education.
■
DISCUSSION
In this series of lab experiments, students were guided to review
their synthesis and analytical evidence in order to provide a
claim of whether domestic soybean oil can be used as a
feedstock in the development of a viable alternative fuel. The
classroom data indicated that FAMEs could be synthesized in
relatively high yields from a renewable starting material.
Furthermore, the samples prepared by the students (B100
and B20) were reliable sources of energy that produced values
that were lower in terms of energy density and heat value when
compared with a commercially available petroleum source.
These overall energy depressions reported by the students
follow known trends when comparing fatty acid methyl esters
with Diesel No. 2. It has been reported that B100 (from
soybeans) provides 8% less energy47 and B20 demonstrates a
1.73% decrease in energy48 when compared to Diesel No 2.
The ability of high school students to produce analytical data
that expands their scientific understanding of thermodynamics,
energy densities, specific heat, and heat value equipped the
students to synthesize their own understanding of the viability
of various alternative fuels.
In assessing the implementation of this lab, a high school
teacher who piloted the series of experiments with students in a
classroom setting provided the following insights. First, the
materials and procedure were appropriate for high school
students. Second, calculating the combustion enthalpy (using
specific heat) of a renewable fuel provided a valuable concrete
experience that allowed the students to formalize abstract topics
regarding energy. Lastly, following the implementation of the
lab series, the student participants have reiterated their findings
in science and environmental student club meetings. Witnessing the students engaged in relevant discussions of stewardship
and green technologies well beyond the classroom walls has
reaffirmed the positive impact of the experience upon the
students’ thinking.
■
REFERENCES
(1) World Commission on Environment and Development. Our
Common Future. Oxford University Press: Oxford, 1987.
(2) American Chemical Society Web Site for Standards, Guidelines,
and ACS Approval Program. http://portal.acs.org/portal/
PublicWebSite/education/policies/index.htm (accessed Jun 2014).
(3) Science Education Science Standards; National Academy of Science:
Washington, DC, 1996.
(4) King, A. G.; Wright, M. W. Rudolph Diesel Meets the Soybean:
“Greasing” the Wheels of Chemical Education. J. Chem. Educ. 2007,
84, 202.
(5) National Academies, Committee on Conceptual Framework for
the New K-12 Science Education Standards; National Research
Council. A Framework for K-12 Science Education: Practices.
Crosscutting Concepts and Core Ideas; The National Academies Press:
Washington, DC, 2012.
(6) The Next Generation Science Standards: Executive Summary.
http://www.nextgenscience.org/sites/ngss/files/
Final%20Release%20NGSS%20Front%20Matter%20-%206.17.
13%20Update_0.pdf (accessed Jun 2014).
(7) Definition of Energy (PS3A) and Energy in Chemical Processes
and Everyday Life (PS3D) are found in Appendix E - Progressions
within the Next Generation Science Standards. http://www.
nextgenscience.org/sites/ngss/files/Appendix%20E%20%20Progressions%20within%20NGSS%20-%20052213.pdf (accessed
Jun 2014).
(8) Appendix G - Crosscutting Concepts. http://www.
n e x t g e n s c ie n c e . o r g / s i t e s / n g s s /fi l e s / A p p e n d i x % 2 0 G % 2 0 %20Crosscutting%20Concepts%20FINAL%20edited%204.10.13.pdf
(accessed Jun 2014).
(9) Fisher, M. A. Chemistry and the Challenge of Sustainability. J.
Chem. Educ. 2012, 89, 179−180.
(10) Clark, R. A.; Stock, A. E.; Zovinka, E. P. Metalloporphyrins as
Oxidation Catalysts: Moving Toward “Greener” Chemistry in the
Inorganic Chemistry Laboratory. J. Chem. Educ. 2012, 89, 271−275.
(11) Moore, J. W. Energy. J. Chem. Educ. 2008, 85, 891.
Summary
This investigation engages students in scientific questioning,
generating evidence, and analyzing data to address questions of
environmental stewardship. This experiment expands on
C
dx.doi.org/10.1021/ed400436z | J. Chem. Educ. XXXX, XXX, XXX−XXX
Journal of Chemical Education
Laboratory Experiment
(12) U.S. Energy Information Agency, Annual Energy Review 2012.
http://www.eia.gov/totalenergy/data/annual/index.cfm (accessed Jun
2014).
(13) U.S. Energy Information Agency, Sales of Distillate Fuel Oil by
End Use. http://www.eia.gov/dnav/pet/pet_cons_821dst_dcu_nus_
a.htm (accessed Jun 2014).
(14) Tat, M. E.; VanGerpen, J. H. The Specific Gravity of Biodiesel
and Its Blends With Diesel Fuel. Am. Oil. Chem. Soc. 2000, 77, 115−
119.
(15) National Renewable Energy Laboratories. Biodiesel Handling
and Use Guidelines (revised 2009). http://www.nrel.gov/
vehiclesandfuels/pdfs/43672.pdf (accessed Jun 2014).
(16) Johnston, M.; Holloway, T. A Global Comparison of National
Biodiesel Production Potentials. Environ. Sci. Technol. 2007, 41, 7967−
7973.
(17) Petroleum & Other Liquids - U.S. Energy Information
Administration (EIA). http://www.eia.gov/petroleum/ (accessed Jun
2014).
(18) King, A. Research Advances: Fill ’Er Up on Chicken, Shrimp,
and Coffee? J. Chem. Educ. 2010, 87, 243−244.
(19) Wallington, T. J.; Anderson, J. E.; Siegel, D. J.; Tamor, M. A.;
Mueller, S. A.; Winkler, S. L.; Nielsen, O. J. Sustainable Mobility,
Future Fuels, and the Periodic Table. J. Chem. Educ. 2013, 90, 440−
445.
(20) Kovacs, D. G. ConfChem Conference on Educating the Next
Generation: Green and Sustainable ChemistryTeaching Green
Chemistry: The Driving Force behind the Numbers! J. Chem. Educ.
2013, 90, 517−518.
(21) Cummings, S. D. ConfChem Conference on Educating the Next
Generation: Green and Sustainable ChemistrySolar Energy: A
Chemistry Course on Sustainability for General Science Education and
Quantitative Reasoning. J. Chem. Educ. 2013, 90, 523−524.
(22) Shane, J. W.; Bennett, S. D.; Hirschl-Mike, R. Using Chemistry
as a Medium for Energy Education: Suggestions for Content and
Pedagogy in a Nonmajors Course. J. Chem. Educ. 2010, 87, 1166−
1170.
(23) Shultz, M. J.; Kelly, M.; Paritsky, L.; Wagner, J. A Theme-Based
Course: Hydrogen as the Fuel of the Future. J. Chem. Educ. 2009, 86,
1051.
(24) Mascal, M.; Scown, R. Converting Municipal Waste Into
Automobile Fuel: Ethanol from Newspaper. J. Chem. Educ. 2008, 85,
546.
(25) Goheen, D. W. Chemicals from Wood and Other Biomass. Part
I: Future Supply of Organic Chemicals. J. Chem. Educ. 1981, 58, 465.
(26) Blatti, J. L.; Burkart, M. D. Releasing Stored Solar Energy within
Pond Scum: Biodiesel from Algal Lipids. J. Chem. Educ. 2012, 89,
239−242.
(27) Long, S. The Science Teacher: March 2009 through November
2009. J. Chem. Educ. 2010, 87, 239−242.
(28) Van Seters, J. R.; P, J.; Sijbers, J.; Denis, M.; Tramper, J. Build
Your Own Second-Generation Bioethanol Plant in the Classroom! J.
Chem. Educ. 2010, 88, 195−196.
(29) Hoffman, A. R.; Britton, S. L.; Cadwell, K. D.; Walz, K. A. An
Integrated Approach to Introducing Biofuels, Flash Point, and Vapor
Pressure Concepts into an Introductory College Chemistry Lab. J.
Chem. Educ. 2011, 88, 197−200.
(30) MacArthur, A. H. R.; Copper, C. L. Alternative Fuels and
Hybrid Technology. A Classroom Activity Designed to Evaluate a
Contemporary Problem. J. Chem. Educ. 2009, 86, 1049.
(31) Environmental Protection Agency. http://www.epa.gov/otaq/
fuels/renewablefuels/index.htm (accessed Jun 2014).
(32) Bladt, D.; Murray, S.; Gitch, B.; Trout, H.; Liberko, C. AcidCatalyzed Preparation of Biodiesel from Waste Vegetable Oil: An
Experiment for the Undergraduate Organic Chemistry Laboratory. J.
Chem. Educ. 2011, 88, 201−203.
(33) Clarke, N. R.; Casey, J. P.; Brown, E. D.; Oneyma, E.; Donaghy,
K. J. Preparation and Viscosity of Biodiesel from New and Used
Vegetable Oil. An Inquiry-Based Environmental Chemistry Laboratory. J. Chem. Educ. 2006, 83, 257.
(34) Bucholtz, E. C. Biodiesel Synthesis and Evaluation: An Organic
Chemistry Experiment. J. Chem. Educ. 2007, 84, 296.
(35) Pohl, N. L. B.; Streff, J. M.; Brokman, S. Evaluating
Sustainability: Soap Versus Biodiesel Production from Plant Oils. J.
Chem. Educ. 2012, 89, 1053−1056.
(36) Bardole, J.; Weaver, G. Conducting Undergraduate Research at
Vincennes University. J. Chem. Educ. 2010, 87, 1131−1132.
(37) Wagner, E. P.; Koehle, M. A.; Moyle, T. M.; Lambert, P. D.
How Green Is Your Fuel? J. Chem. Educ. 2010, 87, 711−713.
(38) Feng, Z. V.; Buchman, J. T. Instrumental Analysis of Biodiesel
Content in Commercial Diesel Blends: An Experiment for Undergraduate Analytical Chemistry. J. Chem. Educ. 2012, 89, 1561−1565.
(39) Ault, A. P.; Pomeroy, R. Quantitative Investigations of Biodiesel
Fuel Using Infrared Spectroscopy: An Instrumental Analysis Experiment for Undergraduate Chemistry Students. J. Chem. Educ. 2012, 89,
243−247.
(40) Pierce, K. M.; Schale, S. P.; Le, T. M.; Larson, J. C. An Advanced
Analytical Chemistry Experiment Using Gas ChromatographyMass
Spectrometry, MATLAB, and Chemometrics to Predict Biodiesel
Blend Percent Composition. J. Chem. Educ. 2011, 88, 806−810.
(41) El Seoud, O. A.; Loffredo, C.; Galgano, P. D.; Sato, B. M.;
Reichardt, C. Have Biofuel, Will Travel: A Colorful Experiment and a
Different Approach to Teach the Undergraduate Laboratory. J. Chem.
Educ. 2011, 88, 1293−1297.
(42) (a) Akers, S. M.; Conkle, J. L.; Thomas, S. N.; Rider, K. B.
Determination of the Heat of Combustion of Biodiesel Using Bomb
Calorimetry. A Multidisciplinary Undergraduate Chemistry Experiment. J. Chem. Educ. 2006, 83, 260. (b) Baroi, C. Y.; Yanful, E. K.;
Bergougnou, M. A. Biodiesel Production from Jatropha curcas Oil
Using Potassium Carbonate as an Unsupported Catalyst. Int. J. Chem.
React. Eng. 2009, 7 (A72), 1−18.
(43) Behnia, M. S.; Emerson, D. W.; Steinberg, S. M.; Alwis, R. M.;
Dueñas, J. A.; Serafino, J. O. A Simple, Safe Method for Preparation of
Biodiesel. J. Chem. Educ. 2011, 88, 1290−1292.
(44) Brouwer, H. Small-scale Thermochemistry Experiment. J. Chem.
Educ. 1991, 68, A178.
(45) Yanmar: Industrial Diesel Engine. http://us.yanmar.com/
products/industrial-engines/air-cooled/epa-certified/l-v-series/l100v/
(accessed Jun 2014).
(46) U.S. Environmental Protection Agency, Non-commercial and
Home Biodiesel Waste. http://www.epa.gov/region7/biofuels/
noncombiodiesel/waste.htm (accessed Jun 2014).
(47) National Renewable Energy Laboratories. Biodiesel Handling
and Use Guidelines (revised 2009). http://www.nrel.gov/
vehiclesandfuels/pdfs/43672.pdf (accessed Jun 2014).
(48) A Comprehensive Analysis of Biodiesel Impacts on Exhaust
Emissions; U.S. Environmental Protection Agency: EPA420-P-02-001,
October 2002.
D
dx.doi.org/10.1021/ed400436z | J. Chem. Educ. XXXX, XXX, XXX−XXX