The Modern Student laboratory : Exploring the Environment The Analysis of Sulfur in Coal An Ion Chromatography Experiment Edward Koubek and Alexander E. Stewart US. Naval Academy, Annapolis, MD 21402
Ion chromatography is used in this analysis to determine the sulfur content in coal. The sulfur is converted into soluble sulfate by heating the coal overnight with a mixture of MgO and NazC03a t 800 'C. The resulting sulfate is dissolved in a known volume of solution and determined via ion chromatography. This method is well-suited for use as an undergraduate laboratory experiment as it requires the student to utilize both wet and instrumental techniques to perform the entire analysis. Also, since it is a real analysis with environmental implications, it generates student interest. Three different, pre-analyzed, powdered coal samples were used in this experiment. These were 3.00% sulfur NBS-analyzed coal, which served as our reference, and two other samples obtained from the Potomac Electric Power Company (PEPCO), one 2.16% sulfur and the other 2.05% sulfur. Several other previously analyzed' samples were generously donated by PEPCO. These range from 1.77%to 2.24% sulfur and serve as convenient student unknowns.
room temperature and diluted to the mark with deionized water. Before the "unknown" solutions are analyzed, another five- to tenfold dilution is necessary to get the resulting sulfate concentrations within the range of the working calibration curves.
Procedure for Conversion of Sulfur in Coal to Soluble Sulfate Coal samples weighing approximately 1g are weighed out in clean porcelain crucibles. Then approximately 3 g of Eschka mixture (2) (2 parts by weight MgO and 1part
Results and Discussion
NazCO8)is added to each crucible containing a coal sample. Using a spatula, the sample is thoroughly mixed and the mixture lightly packed by gently tapping the crucible on a hard flat surface. Then another gram of Eschka mixture is used to cover the original mixture, and the crucibles are covered and olaced overnight in a muffle furnace a t 800 'C. The next Aorning the agsence of all black particles indicates comolete reaction. The reactions takine olace involving sulfur'may he represented as follows:
-.
After being cooled to room temperature, each crucible is emptied into its own 150-mL beaker containing 100 mL of deionized water. The contents and crucibles are heated on a steam bath with occasional stirring for approximately 20 min. These solutions are filtered (Whatman #1) directly into 250-mL volumetric flasks, with all insoluble matter being washed (3x1 with hot deionized water. Each solution is neutralized with 6 M HC1, using phenolphthalein as the indicator. The flasks and contents are allowed to cool to
Ion Chromatography
All ion chromatograms are obtained on a Waters ILC-1 single-column ion chromatograph equipped with a Waters Pak A HR anion column and a Waters Model 430 conductivity detector. A helium-sparged 1.0 mM KHP solution is used for elution and gives a sulfate retention time in the order of 12 min a t a flow rate of 1mumin. Working calibration curves are made on solutions prepared from primary standard ammonium sulfate and diluted to the range of 10-50 ppm. POLFIT*** on the Naval Academy !bme Sharing system is utilized in calculating the equation for calibration curves. All "unknowns" are run on the same day as the calibration curves. Sample student results are given in the table. Four coal samples were weighed out by the student: one NBS 3.00% S, one PEPCO 2.05% S, and two PEPCO 2.16% S. Each coal sample was mixed with Eschka mixture and heated overnight a t 800 'C. After treatment and dilution, the NBS sample was injected three times while the other three samples were analyzed twice. In general, reproducible and Sample Results
Sample NBS
Trial
Coal Mass(g)
%Sulfur % Deviation Found
1
1.0057
2.90
-3.3
PEPCO
1
1.0261
2.05
0.0
2.05%S
2
1.0261
2.04
4.7
PEPCO
1
1.0208
2.09
-3.3
2.16%S
2
1.0208
2.07
4.3
'Analyzed by the ASTM Bomb Washing Method. Sulfuris precipitated as BaSO6from oxygen-bombcalorimeter washings ( 1 ) . A146
Journal of Chemical Education
(Continued on page A148)
The Modern Student loborotory: Exploring the Environment good results are obtained. Small deviations toward the low side are more common than high results. However, this method gives results that are very suitable for use in an undergraduate course. The entire analysis can be carried out during a one-afternoon laboratory provided that previously ignited samples are available. However, since we found no problem with sample storage, students can ignite samples during one laboratory period and analyze them during the next. There are no major safety problems. Performing this experiment always leads to discnssion of why one does a sulfur analysis in the first place (31, as well as how one samples a coal pile 50 ft high by 500 R long (4). Also, the "burning" of coal in the presence of basic metal oxides and carbonates demonstrates an alternative
method for the prevention of SO2emission into the atmosphere, which can also lead to further discussion (5). Acknowledgment We would like t o thank J. A. DuVall, PEPCO, Chalk
Point Station, for donating several pre-analyzed coal samples and J. C. Colbert, National Institute of Standards and Technology, for donating the NBS coal sample. Literature Cited 1.1988Annuol Bmk ofASTM Standords,5, aec. 5, p 308. 2. Selvlg, W A,; Fieldner,A. C. Ind. ondEng ChDm lm,19 161, 729. 3. (a) Brieker, 0. P: Rice, K . C. Enuimn. Sci Tochnd. 198823, 379 1b) Bruce, N. J. Enuimnmnfal C h i s b y ; Wuuz: W?nnipeg,Canada, 1991: pp 146178. 4. Hams,D. C. Quonritatiua Chamled Andy&, 2nd ed.; W. H. Reeman: New York, 1981; pp W 4 . 5. Manahan. S. E E n u i m m n h l Chrahy.4thed.: BmokYCole: Monterqi CA, 1984, pp 33%334.
Atmospheric Smog Analysis in a Balloon using FTIR Spectroscopy A Novel Experiment for the Introductory Laboratory Ralph L. Amey Norris Hall of Chemistry, Occidental College, Los Angeles, CA 90041
One of the persistent complaints regarding general chemistry laboratory is that the experiments are boring and irrelevant (1,2).This point manifests itself in the national trend of students leaving chemistry, frequently after only one year (3). In our department we believe that one way to reverse this trend is to incorporate modern instrumentation into the laboratory early and often. Unfortunately, many modern instruments are unsuited for massive hands-on use by freshman students. They are expensive, complicated, and vulnerable to breakdown in the middle of a lab session. With the commercial development of reliable and sturdy Fourier transform instruments, however, we can now have entire classes of students make individual measurements in a single laboratory period (4). AFourier transform infrared (FTIR) spectrophotometer is a natural instrument for integration into the general chemistry laboratory. Although the principles of interferometry and the Fourier transform are rather complex (51, the fundamentals of infrared spectroscopy are grasped easily (6). FTIR instruments are simple to operate. In many general chemistry courses, infrared spectroscopy can be introduced as early as the third week. At that time, the students are taught the relationship between vibrational frequency and bond order and that different bonds absorb at different regions in the infrared spectrum. A148
Journal of Chemical Education
A Simple Experiment
At Occidental College we have developed a simple experiment that examines and identifies some of the components of Los Angeles air by FTIR spectroscopy using an inexpensive toy balloon as a sample gas cell. The balloon is filled to a constant, easily reproduced diameter that is determined by passing it through a laboratory iron ring supplied to each student. The balloon is then placed on a suitably sized cork ring that is centered and taped to the floor of the FTIR's sample compartment. This simple procedure provides the student with a sufficiently reproducible pathlength for the generation of qualitatively distinguishable difference spectra. Students are led through inquiry and observation to discover (4, 7) the identity of each gas from its characteristic spectrum. First they fill the balloon with dry air or nitrogen from a cylinder source and measure the spectrum. Then they refill the balloon with a selection of other gases prepared in a variety of ways. Experimental Spectroscopic Equipment
Spectra were collected with a Beckman FT2100 FTIR spectrophotometer at 8 CII-' resolution averaged over 25 scans with triangular apodization. Data were transferred to an MS DOS-based computer and analyzed using Spectra-Calc software from Galactic Industries. Although a higher resolution could be chosen and more scans could be
