Chem. Educator 2008, 13, 87–91
87
Electronic Qualitative Analysis Schemes: Student-Developed Chemical
Riddles Cross Borders
Thomas J. Manning,* † Aurora Pérez Gramatges,* ‡Sofia Ullah,† Peter Vu, † Landon Lasseter, †
Vineet Kumar, † Jeff Felton, † C.J. Mock† and Geyser Fernández‡
†
Department of Chemistry, Valdosta State University, Valdosta, GA 31698, tmanning@valdosta.edu,
Departamento de Radioquímica, Facultad de Ciencias y Tecnologías Nucleares, Instituto Superior de
Tecnologías y Ciencias Aplicadas (InSTEC), Quinta de los Molinos, Ciudad de La Habana, Cuba, A.P. 6163,
apgram@instec.cu
‡
Received March 4, 2007. Accepted June 4, 2007.
Abstract: Students in Cuba and the United States participate in a joint exercise entitled Electronic Qualitative
Analysis Schemes (EQAS). In this novel exercise students are taught how to develop and write an EQAS in a
spreadsheet. Students develop a series of questions that allows other participants to identify a chemical group,
then a specific element or simple molecule. Once developed and tested, students exchange their riddles and use a
binary code to help determine their unknown species. Each code turns on certain statements that allow students to
solve the problem. The entire periodic table and a series of simple molecules can be covered in this exercise. An
assessment finds that most general chemistry students participating in the project advanced their knowledge of
elemental properties as well as further developed their ability to work with spreadsheets. The American students
used an English version of the exercise while students in Havana (Cuba) used a Spanish version. The
collaboration was the result of a trip by an American Chemical Society delegation to a conference held in Havana
in October, 2006.
Introduction
Traditional qualitative analysis schemes involve the
separation and identification of various water-soluble ions by
precipitation, odor, color changes in solution, or solids or
flame tests [1–6]. Using a simple example, separating and
identifying Ag+, NH4+, and Na+ in the aqueous phase can be
achieved in a three-step scheme. First Ag+ is separated and
detected by adding chloride (i.e., KCl) resulting in a white
precipitate. Second, the solutions pH is shifted by the addition
of a strong base (i.e., KOH) resulting in
NH4+(aq) + OH–(aq) → NH3(aq) + H2O(aq)
(1)
NH3 is more volatile than NH4+ and can be detected by
smell. Finally the presence of the Na+ cation can be detected
with the flame test. The sodium doublet is a strong emitter of
yellow light (589 nm) that is easily observed. Because modern
equipment allows for multielement analysis at parts per billion
(or lower!) levels (i.e,. ICP-MS) and because these schemes
only deal with a small numbers of elements and emphasize
very specific properties, a more rounded educational exercise
is sought to teach elemental properties and periodic trends.
Also, qual schemes conducted in the lab produce compounds
that often need special disposal, and there are economic factors
associated with purchasing and using chemicals on a large
scale in a teaching lab. While the concept of an experimental
qual scheme is recognized as an excellent method to teach
some chemical properties, an alternative computer based
scheme was been developed that incorporates more elements
and properties [5].
In this exercise we develop a new approach to using the
concepts of qualitative analysis as an educational tool. First
students develop the electronic qualitative analysis schemes for
approximately 98 elements and a number of simple molecular
ions based on chemical and physical properties. Second they
exchange the EQAS and solve them learning a host of periodic
trends and chemical properties along the way. Each student or
group in the lab is assigned between 4 and 8 species with
similar characteristics. For example one student may have Li,
Na, K, Rb, Cs, and Fr, while another student may have the first
seven lanthanides (La, Ce, Pr, Nd, Pm, Sm, Eu). Considering
there are approximately 100 elements and over twenty
prominent molecular ions (i.e., Cl–, O2–, OH–, SO42–, etc.), a
group of 22 students can cover the entire periodic table and
some common molecular species in one or two three-hour lab
periods. If smaller numbers of students are involved, some
chemical groups can be eliminated or the number of species
provided to students can be increased (i.e., all lanthanides are
combined into one group).
First students are given a previously developed electronic
qual scheme for the alkali metals to enter into Excel. This is
used to teach the concept of the electronic qualitative analysis
scheme and the specifics of the programming in a step-by-step
fashion. Students are also given the answer keys to alkali
program and ask to test their version. Once this is complete,
students are given their own group of elements and develop an
electronic qual scheme for their assigned group. Upon
completing their scheme and having it checked by an
instructor, the schemes are exchanged and students must solve
the electronic qualitative analysis schemes developed by their
classmates.
This exercise was successfully conducted on a large scale by
a group of Cuban students from the Instituto Superior de
Tecnologías y Ciencias Aplicadas (InSTEC) in Havana and a
group of American students enrolled in a general chemistry
© 2008 The Chemical Educator, S1430-4171(07) 22123-2, Published on Web 4/1/2008, 10.1333/s00897082123a, 13080087tm.pdf
88
Chem. Educator, Vol. 13, No. 2, 2008
course at Valdosta State University (Valdosta, GA). In October
of 2006 the American Chemical Society had a delegation of
chemists travel to Havana and participate in the 27th Latin
American Congress on Chemistry and the 6th International
Congress on Chemistry and Chemical Engineering conferences
that were held simultaneously. This gave Cuban and American
scientists and opportunity to freely communicate and initiate
collaborations.
Materials and Methods
In this exercise students were granted access to Wikipedia
and their general chemistry textbooks for information needed
to develop their electronic qualitative analysis schemes.
Computers with Microsoft Excel and Internet access were used
in the exercise. Sixty students enrolled in the second semester
of a general vhemistry course from the College of Arts and
Sciences at Valdosta State University (Valdosta, GA) and
thirteen students from Instituto Superior de Tecnologías y
Ciencias Aplicadas (InSTEC) (Havana, Cuba) participated in
the exercise.
Discussion
In terms of writing the electronic qualitative analysis
scheme, there are some rules that need to be followed by the
student authors. The specific role of each rule will become
more evident after students enter and test the practice alkali
metal scheme outlined below. The rules of devising these
chemical riddles are:
1. The number of questions asked for the whole qualitative
scheme should be three times the number of elements. So six
elements should have a total of 18 questions. These questions
will allow the participant to identify both the group they are
dealing with and the specific element.
2. There should be an agreed upon reference source (or
sources) that all participants have easy access to (i.e. textbook,
Wikepedia, Los Alamos Periodic table, etc.).
3. Participants can not incorporate obvious questions (i.e.
your element has the symbol H, what is it?) or extraordinarily
vague questions (i.e. your element has less than 150 protons)
4. There should be a minimum of three questions that allows
the student to identify the group.
5. There should be at least one unique question that allows
the person to identify the element.
6. There will be a minimum of one question in the scheme
related to electron configurations.
7. There will be a minimum of one question in the scheme
related to density, thermal conductivity or electrical
conductivity.
8. There will be a minimum of one question in the scheme
on spectroscopy (light emitted or absorbed). It can be over any
wavelength region (i.e. IR, gamma, etc.) or involve an
application.
9. There will be a minimum of one question in the scheme
related to phase properties (solid, liquid, gas, triple point,
melting point, boiling point, etc.)
10. There will be a minimum of one question on the original
source of the element or specific mineral sources.
11. There will be a minimum of one question on related to
electronegativity, ionization potential, or atomic radius.
12. There will be a minimum of one question on
electrochemical properties (reduction potentials, etc.)
Manning et al.
13. There will be a minimum of one question related to
radioactivity or isotopes.
14. There will be a minimum of one question related to
solubility in a solvent.
15. There will be a minimum of one question on oxidation
states in salts or water.
16. There will be a minimum of one question on industrial
applications or history.
17. In rules 6-16, there may be cases where conditions are
combined in a single question. For example the question,
“Your element is a dication when dissolved in water, its
nucleus strongly absorbs x-rays and it will precipitate out of
solution when mixed with a sulfate.” BUT remember any data
has to fit within the Excel box so long statements are not
always practical.
18. The participant that makes up the qual scheme will also
make up the numerical codes and answer keys in Microsoft
Word.
19. Each element will have its own code represented by a
series of 1s and 0s. The student that makes up a particular qual
scheme will make up the codes for each element in their
particular group.
20. Each group has its own set of codes based that appear
“1011011000111110” these are entered, 1 digit at a time, in
the A column (going down). The clues should appear in the B
column.
21. Participants are instructed to adjust the width of their
Excel columns (output) so all words are visible.
22. In terms of the types of questions (for example, “There
will be a minimum of one question on radioactivity or
isotopes”), this does not mean you should have one question
like this for every element in your group but rather one
question in your scheme related to any element in your group
from this area.
In most general chemistry courses, topics such as
thermochemistry, nuclear chemistry and coordination
chemistry are addressed separately. By having a breathe of
topics to include in their qual schemes helps students tie
together many aspects of periodic trends and chemical
properties. Below are the step-by-step instructions to construct
a qual scheme for the alkali metals.
1. Open a new Excel Sheet. Leave A1…A18 empty.
Later you will enter and test your codes in these locations.
In
B1
enter
the
logic
statement:
“ =IF(A1=1,"Your group has a +1 charge in salts","") “
Be sure to expand the B column so the text you enter is
visible to the reader. Once the statement above is entered, you
can enter the number “1” in A1 to see how it appears in B1.
The above statement helps the student identify what group the
element is in. All elements in this group would have a 1 as the
first digit.
2.
In
B2
enter
the
statement:
“=IF(A2=1,"Your group reacts violently with water in its
metallic form","")”
This also applies to all of the alkali metals so it would be a
“1” for all codes.
3.
In
B3
type
the
statement:
“=IF(A3=1,"Your group has a +1 charge when dissolved in
water","")”
© 2008 The Chemical Educator, S1430-4171(07) 22123-2, Published on Web 4/1/2008, 10.1333/s00897082123a, 13080087tm.pdf
Electronic Qualitative Analysis Schemes: Student-Developed Chemical Riddles…
Table 1. Sample Output in Excel. These Clues Allow the Participant
to Deduce Their Group and Element
1
1
1
1
0
1
1
0
0
0
1
0
0
1
0
0
0
0
Your group has a +1 charge in salts
Your group reacts violently with water when its in neutral form
Your group has a +1 charge dissolved in water
Your group forms strong electrolytes with the halides
This element is soluble in most forms, except as a feldspar
Your element omits yellow light at 589 nm
Your elements outer electron is spin up - in the neutral state
Forms a compound called halite
Chem. Educator, Vol. 13, No. 2, 2008
89
More than one element can be isolated from a brine pool
(although the South American abundance helps narrow it
down!) but the isotope points directly to lithium. At this point
the code for Li is 111100001.
10. In box B10 enter the logic statement:
“=IF(A10=1,"XAg4I5 has the highest room temperature
conductivity of any known ionic crystal","")”
Subscripts (Ag4I5) are not entered in a spreadsheet header
and X stands for Rb.
11.
In
location
B11
enter
the
statement:
“=IF(A11=1,"Your elements outer electron is spin up - in a
neutral state","")”
This statement applies to all of the elements in the alkali
group because its outer electron is the s1 (Li, 2s1; Na 3s1; K,
4s1; Rb, 5s1; Cs, 6s1; Fr, 7s1). The order of the questions, in
terms of groups or elements, should be random.
12. In location B12 enter the logic command:
“=IF(A12=1,"only 340 to 550 grams of element in the
earth's crust.","")”
Because all alkalis are M1+(aq), this would be a 1 in the 3rd
place in the code.
4.
In
B4
enter
the
logic
command:
“=IF(A4=1,"They are strong electrolytes when bound to the
halides","")”
Because all alkali metals dissociate 100% when bound to F–,
Cl , Br– or I–, this would be a 1 in the 4th location.
–
5.
In
B5
type
the
logic
statement:
“=IF(A5=1,"Your element has a melting point of 28 oC","")”
This physical trait applies to only one element (i.e., Cs). So
if the element is Cs, enter a 1 in this place but if it’s another
element enter a 0. If this element is Cs, the code would appear
as 11111..(Q1-5), but if it’s Na it would appear as 11110 (so
far!)
6.
In
location
B6
type
the
statement:
“=IF(A6=1,"This element is soluble in most forms, except
as a feldspar","")”
Because the group has already been identified, elements also
found in feldspars (i.e. Al, Ca) would not be considered but
both potassium and sodium are possibilities. Later questions
will help narrow the choice to one. After the first six questions,
the Na or K code would appear as 111101…; Cs would appear
as 111110…; and Li, Rb, and Fr would be 111100.
7.
In
box
B7
enter
the
logic
statement:
“=IF(A7=1,"Your element omits yellow light at 589 nm","")”
This physical trait belongs to sodium and, along with
#6, helps identify the specific element. At this point Na would
be 1111011 but K would be 1111010.
8. In location B8 enter the logic statement:
“=IF(A8=1,"Your element is the second least dense metal
after lithium","")”
The specific value for the physical property (density) is not
given forcing the student to review the alkali metal densities.
9.
In
location
B9
type:
“=IF(A9=1,"Your element is produced by Chile and
Argentina and is found in Brine pools. X-6 is one its
isotopes","")”
The reason why Francium is rarely mentioned in most
undergraduate courses should be obvious, despite occupying a
strategic corner of the periodic table.
13.
In
“=IF (A13=1,"Least
element","")”
location
B13
electronegative of any
type:
known
While most academic arguments of electronegativity end
with Cs, this forces students to identify the element in the
lower left corner of the periodic table.
14. In box B14, enter the logic statement:
“=IF (A14=1,"Forms a compound called halite","")”
Commonly called rock salt, sodium chlorides more technical
or mineral based nameis halite.
15.
In
box
B15,
enter
the
command:
“=IF(A15=1,"Its pure form is a grey-white metal an it readily
substitutes for potassium in minerals.","")”
This physical description can be applied to more than one
metal but Rb does substitute for K in a number of minerals.
16. In box B16, enter the logic statement:
“=IF(A16=1,"Its chloride salt can be used to stop the
heart,","")”
KCl is utilized in heart surgery and lethal injections to stop
the hearts rhythm.
17.
In
location
B17
type:
“=IF(A17=1,"Its reduction potential for the M+ => M(s) is 2.925 V","")”
This forces the student to review all of the reduction
potentials for elements in this group.
18. In location B18 type the logic command:
“=IF(A18=1,"Its Heat of Fusion is 63.9 kJ/mol, over ten
times higher than water!","")”
A range of thermodynamic or physical parameters can be
selected (fusion, vaporization, sublimination, etc.).
Table 1 provides the output for sodium. The code for this
element would be given as 111101100010010000. A student
can use these clues to deduce that they have an alkali metal but
also that it is Na. While this particular flow chart focused on
© 2008 The Chemical Educator, S1430-4171(07) 22123-2, Published on Web 4/1/2008, 10.1333/s00897082123a, 13080087tm.pdf
90
Chem. Educator, Vol. 13, No. 2, 2008
Table 2. The Binary Codes for Each Element Are Listed Below. Enter
These Codes Individually to Check That Your Electronic Qualitative
Analysis Scheme Is Functioning. When Students Develop a
Qualitative Analysis Scheme, They Will Develop an Answer Key
with This Format In Microsoft Word
Element
Li
Na
K
Rb
Cs
Fr
Code
111100001010000000
111101100010010000
111101010010000110
111100000110001000
111100000010000001
111100000011100000
Table 3. The Periodic Table and a Number of Prominent Molecular
Anions Are Combined To Form Twenty-Two Groups.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16.
17.
18.
19.
20.
21.
22.
Name
Alkali metal (1A)
Gases (8A)
Alkaline earth (2A)
Transition metals (3B,
4B)
Lanthanides I
Metalloids
Actinides I
Transition metals (5B,
6B)
Lanthanides II
Halogens
Soft metals
Nonmetals
Transition metals
7B,1B
Transition metals 8B
Actinides II
Transition Metals 8B,
2B
Soft metals II
Sulfur, Oxygen based
anions
Carbon, nitrogen,
phosphorous based
anions
Halogen based
oxyanions
Metal and metalloid
based anions
Halides (ask halide
chemistry specific
questions, different
from element specific
in group 10) and
ammonium
Li, Na, K, Rb, Cs, Fr
H, He, Ne, Ar, Kr, Xe, Rn
Be, Mg, Ca, Sr, Ba, Ra
Sc, Y, Ti, Zr, Hf, La
Ce, Pr, Nd, Pm, Sm, Eu, Gd
B, Si, As, Te, Ge, Sb
Ac, Th, Pa, U, Np, Pu
V,Nb,Ta,Cr,Mo,W
Tb,Dy,Ho,Er,Tm,Yb,Lu
F, Cl, Br, I, At
Al, Ga, In, Sn
C, P, Se, N,O,S
Mn,Tc,Re,Cu,Ag,Au
Fe, Ru,Os,Ir,Rh,Co
Am,Cm,Bk,Cf,Es,Fm,Md,No
Ni, Pd, Pt,Zn,Cd,Hg
Pb, Bi, Po, In, Tl
S2–. SO32–, SO42–, O2–, O2–, O22–,
OHNO3–, NO2–, N3–, CO32–, C4–, C22– ,
PO4-3
ClO4–,ClO3–,ClO2–,ClO–, BrO3–,
IO3–
MnO4–, CrO42–,Cr2O72–, AsO43–,
AgCl2–
F–, Cl–, Br–, I–, NH3, NH4+
the group properties first and the element properties second,
these questions can be presented in a completely random order.
For this particular flowchart, each element would have the
codes shown in Table 2. Participants are encouraged to enter
each of the codes in Table 2 to test there electronic qualitative
analysis scheme.
Once the practice scheme is complete the instructor assigns
each student a number (see Table 3) or assigns a specific group
of elements. Students develop their own electronic qualitative
Manning et al.
analysis scheme following the example and the rules. It is
important for the group to agree upon which references will be
used as there exist a tremendous amount of obscure research
data associated with any element that could be difficult to find.
Participants also develop a separate answer key in the format
shown in Table 2. Students are instructed to test their answer
codes to ensure their accuracy. The qual scheme (Microsoft
Excel file) and answer key (Micorsoft Word document) are
sent, electronically, to the instructor. Students assign the qual
scheme and answer key their name “joe_smith.xls” and
“joe_smith.doc”. The instructor will change the file name to an
unknown identifier (i.e., joe_smith.xls to group_a.xls).
Typically qual schemes are small (approximately 25 kB) so a
group of 22 files can be distributed to an entire class with a
single e-mail communication. The students return these
completed answer codes (Table 4) to the instructor.
This can be a one-, two-, or three-hour computer laboratory
exercise. Starting with a prelab lecture to explain the exercise,
a group of two students can practice the alkali scheme, develop
one of their own with a small number (i.e., 4–5) of elements
and solve another scheme in three hours. For two three-hour
lab periods, students develop schemes with larger numbers of
elements (i.e., 7–8) in one lab period and solve multiple
schemes developed by their classmates in the second lab
period.
Conclusions
Depending on the time constraints, students solve the riddles
for a few elements or the entire periodic table and small
molecule set. Assuming all of the electronic qual schemes are
completed (groups 1–22, Table 3), if students are given all of
the electronic qual schemes it becomes an excellent review not
only of periodic properties and trends but also a range physical
and chemical properties that are covered in general chemistry.
Introducing this exercise in general chemistry, it was
recognized that there exists a wide range of experiences with
computers and spreadsheets. In our assessment of the
experience, most students indicated this was their first
experience with using the logic statements in Excel. Likewise,
the American group indicated the experience was very positive
and enjoyable despite being held on a Sunday afternoon (2–7
pm). While the Cuban students worked individually, the
Americans worked in groups of two or three. In Cuba, the
experience with the lab also showed the convenience of having
an experimental qual scheme done during the same week. The
Cuban students were in an intensive two-week integrative
course, and one of the course labs was an experimental cation
qualitative analysis scheme. They were asked to include, if
suitable, some clues from what they learned in the lab. Even
when some clues where taken from reference and textbooks,
many of the students actually used that recently learned
knowledge to help in identifying the unknown elements. From
our perspective, the exercise done using this combination
reinforced the integrative objective of the course.
This exercise was successfully implemented in American
and Cuban classes within a week of each (Feb 2007). Both
groups of students, Cuban and American, reacted positively to
the experience of collaborating with each other.
Supporting Material. Included are Microsoft Excel and
Word files generated by students. The Excel files contain the
EQAS files developed by different groups of students and the
© 2008 The Chemical Educator, S1430-4171(07) 22123-2, Published on Web 4/1/2008, 10.1333/s00897082123a, 13080087tm.pdf
Electronic Qualitative Analysis Schemes: Student-Developed Chemical Riddles…
Table 4. Example of an Abbreviated Sample Unknown Key. Students
Enter the Code in the Respective File and Research the Answer.
Instructors May Assign One or Two Elements from a Single EQAS or
All Elements and Molecules from All Schemes.
File
group_a
group_b
group_c
group_d
group_e
group_f
Code
111100001010000000
101110110000010100
111101100010010000
001011011000001100
111101010010000110
000101010101011100
111100000110001000
111100000010000001
111100000011100000
Your Answer
Word files contain the answer keys. Also included is the alkali
metals qual scheme file that is outlined in the body of this
paper.
Acknowledgment. We would like to thank the organizers of
the 27th Latin American Chemistry conference including Dr.
Alberto Nuñez, Dr. Roberto Cao and Dr. Irma Castro. The
American Chemical Society is thanked for organizing the trip
Chem. Educator, Vol. 13, No. 2, 2008
91
(Dr. Brad Miller, Dr. Beth Rudd, Dr. Jerry Bell, and Tamara
Nameroff). We would like to thank Valdosta State University
including the chemistry department (Dr. Jim Baxter),
International Programs (Dr. Ivan Nikolov, Dave Starling), Arts
and Sciences (Dr. Linda Calendrillo, Dr. Jim LaPlant),
Academic Affairs (Dr. Louis Levy) and Information
Technology (Joe Newton, Ike Barton) that helped make
various aspects of this project possible.
References and Notes
1.
Packer, J. E. J. Chem. Educ. 1966, 43(4), 197–198.
2.
Prokopov, T. S. Inorganic qualitative analysis in freshman chemistry.
Proceedings of the Iowa Academy of Science 1970, 77, 347–53.
3.
Lambert, J.L.; Meloan, C. E. J. Chem. Educ. (1977), 54(4), 249–52.
4.
Menditto, A; Patriarca, M; Chiodo, F; Morisi, G. The Italian external
quality assessment scheme for trace element analysis in body fluids
Annali dell'Istituto Superiore di Sanita, 1996, 32(2), 261–270.
5.
Woodfield, B. F.; Catlin, H. R.; Jones, D. C.; Woolley, E. M.,
Complete and realistic simulation of inorganic qualitative analysis.
Book of Abstracts, 219th ACS National Meeting, San Francisco, CA,
March 26–30, 2000; CHED-985.
6.
Kirschenbaum, L. J.; Resende, E; Li, E; Ruekberg, B. J. Chem. Educ.
2001, 78(11), 1524.
© 2008 The Chemical Educator, S1430-4171(07) 22123-2, Published on Web 4/1/2008, 10.1333/s00897082123a, 13080087tm.pdf