2 -
CI&
t4.e New England Association of Chern
R. F. O'Malley
Boston College Chestnut Hill, Massachusetts
The Use of Problems from the Literature in General Chemistry
Problems based upon data from the original literature are common in textbooks of physical chemistry (1-4), but not in textbooks of general chemistry. The solution of problems of historical interest was a feature of some of the older British books (5, 6), but usually as illustrations in the text, rather than as problems for the students to solve. Problems illustrating the calculation of atomic weights from experimental data have occasionally included references to the sources of the data (7, 8). The recent iutroductiou into general chemistry of problems formerly met for the first time in physical chemistry has also brought reference to sources of data (9). It is not a generally accepted practice, however. For several years an effort has been made to include as many problems based on the literature as possible in our general chemistry course. During the first semester nearly all of the problems encountered by the students in assienments and examinations have been of this type. The references have been to both older and newer work in order to emphasize what is of permanent value. The practice was begun to indicate to the students the relation of what was taught to the activities of practicing chemists. It was hoped that more interest would be aroused. Experience has shown that additional advantages are derived from the use of actual laboratory data. The introduction to signscant figures is made more meaningful and the fact that measurements involve errors is emphasized. The following problems are mostly from recent assignments and examinations and are presented as illustrative of the various types that are appropriate. An extensive list of problems has been gathered from the regular, necessary reading of current journals. An early introduction to the chemical journals was considered of sufficient importance to include the reference in each problem. After an examination the students were referred to the library in answer to the question, "What is the correct answer to number five?"
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Based on a paper presented at the 321st Meeting of the New England Association of Chemistry Teachers, May, 1963, Clark University, Worcester, Mass.
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In order to acquaint the students with the Journal of Chemical Education, "Solve problems 1-10 in J. CHEM. E ~ u c . 41, , 512 (1964)" will be an assignment in the future. Calculation of Percentage Composition from Formulas 1. In a study of the preparation of fluoroplatinates several compounds were made and the percentage alkaline earth metal present determined hy analysis. Do the values obtained and listed below agree with the values o&ulated from the formulas?
Comoound
?Z M observed
NORR.M. K.. PERROB. T. P.. AND NAESER.C. R.. J. Am. Chem. Soc., 80,5038 (1958). 2. Chemists a t the University of Connecticut heated LaDs with Ti20aat 12WDCand obtained 8. product which contained 20.58% Ti and 58.95% La by ehemiealanalysis. Do these results PI., agree with the calculated composition of LaTiOa? KESTIGAN, am WARD,R., J . Am. Chem. Soc., 76,6027 (1954). 3. Bell and Herfert reacted molyhdenum(1V) oxide with sulfur and obtained a compound which anzlysed: Mo, 60.17%; S. 39.87%. Do these results seree with the cornnosition calcul&dfor'%o~? BELL,R. E., A& HERFERT, R. E.; J. Am. Chcm. Soc., 79, 3351 (1957).
Calculation of Empirical Formulas from Composition 4. An oxide of molybdenum purified for thermodynamic studies at Carnegie Institute of Technology was found to contain 66.870 molybdenum. What is the empirical formula of the compound supported by this evidence? Coscnov~,L. A,, AND S ~ Y DER,P. E., J. Am. Chem. Soe., 75,1227 (1953). 5. A chromium carbide was prepared at the Carboloy Department, of the General Electric Company, by heating chromium oxide with lampblttck. The carbon content was found to be 13.2% and the chromium content 86.2%. What is the empirical formula of the compound? DESORBO, W., J . Am. Chem. Soc., 75, 1825 (1953). 6. A soft violet powder resulted when zirconium dioxide was heated in the presence of carbon diaulfide at 1200°C. A typical analyailysis of the product from one of the experiments was: Zr, 59.68%; S,41.01%. What is the empirical formulaaE the compound? CLEARF~LD, A., J. Am. Chem. Soc., 80, 6511 (1958).
7. What is the simplest formula of the compound which gave the following composition when analyzed: Os, 39.87'; C1, 44.47Z0 and the remainder potassium? LARSON,L. L., AND GARNER, C. S., J. Am. Chem. Soe., 76, 2180 (1954). 8. In a study of the reaction of silicon tetrafluoride with magnesium chloride a liquid boiling at 57.6"C was obtained. The chemical analysis of the compound gave: Si, 16.48%; C1, 83.3%. What was the eompound? SCHUIB, W. C., AND BRECK, D. W., J. Am. Chem. Soc., 74, 1757 (1952). 9. A compound whose molecular weight was found to he 320 gave an elemental analy~ie: W, 49.5%; Br, 20.97'; and C1, 29.3%, when prepared in the inorganic chemistry labarrttory at R. C., MIT. What was the formula of the compound? YOUNG, AND LAUDISE, R. s., J . Am. Chem. See., 78,4861 (1956). 10. Basic eopper(I1) carbonate, CU(OH)~.CUCO~, was added, with stirring, to a twofold excess of 40Yo hydrofluoric acid. After standing several hours with occasional stirring the precipitate which formed was filtered, washed with ethanol, air dried briefly and stored in platinum. A sample, upon analysis, gave the following results
What was the eompound? Write an equation for the reaction. H. M., J . Am. Chem. Soe., 76, WHEELER, C. M., AND HAENDLER, 263 (1954). 11. The preparation and properties of a chloride of silicon was discussed at the 138th ACS Meeting in New York, by Prof. Grant Urry of Purdue University. He presented the following results: Si, 24.9%; C1, 75.3% and a. molecular weight of 667. Give the formula and name of the eompound.
Problems Bosed on the Ideal Gas Law 1. In a study of the constit,uents of Pennsylvania petroleum 0.1113 g of a vapor was found to occupy 59.5 ml at 182-C under a pressure of 354.7 mm of Hg. Calculate the molecular weight of the vapor, assuming that the ideal gas law applies. MABERY, C. F., Am. Chem. J . , 19,426 (1897). 2. In 1957 at the Humboldt University, Berlin, a colorless gas, selenium dioxygen difluoride was prepared. Assuming it to behave as an ideal gas, what volume would be occupied by 0.250 H. G., Angew. g s t 27.2T and 30 mm of Hg? JERSCHKEWLTZ, Chem., 69, 562 (1957). 3. The weight of a liter of an oxide of nitrogen at standard conditions was determined to be 1.97788 g by Lord Rayleigh. What is the molecular weight of the compound? Calculate the atomic weight of nitrogen on the basis of 0 = 16.0000 and 0 = 15.9994. Compare the result,s of your cdculatians with a recent tahle of atomic weights. GMELIN'S"Handbuch der anorganischen Chemie," System No. 4, 114 (1934). 4. Bawter and Starkweather measured the density of a. gas and obtained the following results: 2117.77 ml measured a t 253.333 mm of Hg weighed 0.63556 g a t ODC. If the gas is monatomic, what iis its atomic weight? BAXTER, G. P., AND STARKWEATHER, H. W., Proe. Nut. A d . Sei., 14, 56 (1928). 5. In a study of the thermodynamic properties of arsine, a sample of the gas was collected in a glass apparatus whose volume was one liter. What was the mass of the gas in the bulb a t 25.0°C ilnd 437 mm of Hg? SHERMAN, R. H., AND GIAUPUE,W. F., J. Am. Chem. Soc., 77, 2155 (1955). 6. The vapor density of hydrogen sulfide was carefully measured at McGill University. At 25.00PC and 743.2 mm a. glass bulb of 586.7 ml capacity was filled with the gas. What was the mass of the gas in the bulb? WRIGHT,R. H., AND MAASS,O., Can. J . Res., 5,442 (1931). 7. One liter of a gas was found to weigh 2.66 g a t 20.3"C and 749 mm. What is the molecular weight of the gas? GMELIN'S "Handbuch der anorganischen Chemie," System No. 9, 211 (1953). 8. When the volume of a sample of gas weighing 0.0808 g was measured at 17.3"C and 405.7 mm Hg, it was found to be 128.8 ml. The same sample of gas was then decomposed, and 63.6 mg of boron and 197.3 ml of HZ(measured at standard conditions) were obtained. What is the molecular weight of the gas? What is the formula. of the gas? STOCK,A,, AND KUSS, E., Ber., 56,798 (1923).
9. When boron trichloride was subjected to a high voltage mercury arc, a. pale yellow compound was formed which analyzed: B, 23.0Y0; C1, 75.070. A sample of the compound weighing 0.0516 g occupied s volume of 268 cc a t 69'C and 17.9 mm. What is the formula of the compound? URRY,G., GARRETT, H. I., Znorg. Chem., 2,396 (1963). A. G., A N D SCHLESINGER,
Problems Bosed on Equations 1. Hrtendler, et al. studied the preparation of copper(I1) fluoride by various methods. Direct synthesis from the elements was attempted a t 55M)'C. They reported that 537' of the capper was converted to the fluoride. How many grams of copper(I1) fluoride e m be produced from 10 g. of copper according to their et al., J. Am. Chem. Soe., 76, 2178 (1954). results? HAENDLER, 2. In an effort to prepare pure magnesium iodide 12.0 g of powdered magnesium and 127 g mereury(I1) iodide were heated in a Vycor tube for one hour. If the other product was mercury, which of the starting materials was in excess? BOCKRIS,3. O'.M., AND CROOK,E. H., Chem. Ind., 1959, 1162. 3. An excess of hydrogen peroxide was allowed to react with 10.0 g of tellurium dioxide. The product, HzTeOs, was formed in 75% yield. Name the product. What weight of product was obtained? HORNBR, H. J., AND LEONARD, G. W., JR.,J. Am. Chem. Sac., 74, 3694 (1952). 4. Apple and Wartik of Pennsylvania State University sealed 1.646 mmnles of diboron tetrachloride in an ampoule with an excess of bromine and allowed the mixture to stand a t -22.9-C for several hours. If the only products were boron trichloride and boron trihromide, how many grams of each were formed? APPLE,E. F., A N D WARTIK,T., J. Am. Chem. Soc., 80, 6153 (1958). 5. The hexacarbonyl of molybdenum was prepared in 91% yield according to the following equation: 2MoC15
+ 5Zn + 12CO
-
2Mo(CO)s
+ 5ZnClt
What weight in grams of each product can be obtained from 0.100 mole MoCL and an excess of each of the other reactants? Vor, KOV,V. L., et al., Zhur. Neorg. Khim., 3 , 2433 (1958). 6. Anhydrous UOBh was prepared on the 100 g scale by the following series of reactions:
Approximately 10 times the stoiehiometric quantity of carbon disulfide was passed over the sample during a 3-hr period. Five times the stoiehiometric quantity of bromine was then swept through the reactor over a 5-hr period. What weight of uranium(IV) oxide, carbon disuLide, and bromine were required to preE., A N D WESTRUM, E. F., JR., pare 100 g of UOBr*? GREENBERG, J . A n . Chem. Soc., 78,5144 (1956). 7. An extended program in the preparation of rare earth metals was conducted at Iowa State Univenity. In one series of experiments, 40 g samples of La, Ce, Pr and Gd were prepared from the chlorides by reduction with calcium. Assuming a 90% yield in each case, how many grams of eaah of the chlorides was required to make 40 gram samples of each of the rare earth F. H., AND DAANE, A. H., J . Am. Chem. Soc., metals? SPEDDINU, 74, 2783 (1952). 8. In the following series of reactions, 2.0 g of ReCb were obtained from 1.2 g of Re metal. What was the percentage yield?
- +
4 Re R%O,
+ 7CCClb
+ 701
2 Reno,
2ReCh
7COCL
+ 2C12
KNOX,et al., J. Am. Chem. Soe., 79, 3358 (1954). 9. Cesium was the first element discovered spectroscopically by Bunsen and Kirchaff. They isolated 50 g of cesium ehloroplatinate from which they obtained 17 g of CsCl:
-
+
CslPtCls 2CsC1 PtCL What was the percentage yield? Endeavor, 18,171 (1959). 10. Nitrogen may be prepared by the following reaction: MNOl
+ NH41
-t
2H20
+ N2 + MCI
where M = Li, Na, K, Rh or CS. Which compound will produce
Volume 41, Number 9, September 1964
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the largest volume of nitrogen per gram of stmt.ing material? Chem. Eng. News, 38, Nov. 14, 102 (1960). 11. A sample of AIIr6NHs weighing 0.8913 g was heated to 3 4 0 T at a pressure of 10-2 mm in a. closed system. A total of 1.8 mmoles of ammonia gas was collected. What is the d u e of z in the equation:
AIIa.6NH1 WATT, G. W., 1lOr;fi~ ,-""",.
AND
-
AIIs.(6 - z)NHs
+ zNHa
BRAUN,J. H., J . Am. Chem. Soc., 78, 5495
12. In a study of the hydrolysis of pentaborane, B5H., samples of the compound were treated with 20Yo solutions of water in dioxane. In one experiment 31.2 ce of B;H. (measured at standard conditions) was shaken with excess water in dioxane and yielded 375 cc of hydrogen (at standard conditions). Is the following equation consistent with these results?
B5Ho SHAPIRO,I., (1954).
AND
+ I5HzO
-
5B(OH)a
+ 12H2
WEISS, H.G., J . Am. Chem. Soe., 76, 6020
Atomic Weights
white solid? If they used a 0.1046 mold solution to obtain a molecular weieht of 154.4. what waa the freezine mint of the see". tic acid solution? HOLMES, R. R., AND FORSTNER, J. A., Inorg. Chem., 2, 381 (1963). 2. In a comprehensive study of the ammonia-boron trfiuoride system by Laubengayer and Condike of Cornell Univenity, anhydrous ammonia and boron trfiuoride were mixed in a oneliter flask cooled with ice water. A white powder accumulated in the flask. Its itnaly~iswas: NH., 20.05, 19.90, 19.85; B, 12.80, 12.72, 12.65. Molecular weights determined crymoopically in three aqueous solutions containing, respectively, 15.77, 8.15 and 6.04 g. of the compound per 1000 g. of water were 81.0, 83.9 and 82.4. What is the formula of the compound? What was the freezing point of each of the solutions used for molecular weight determinations? Draw diagrams indicatmg the shapes of the molecules of the stt~rtingmaterialsand the product. LAUBENGAYER, A. W., AND CONDIKE, G. F., 1.Am. Chem. See., 70, 2274 (1948). 3. A compound containing carbon, hydrogen and sulfur was recently prepared in Germany. The molecular weight of the compound was determined cryasoopicslly in benzene (melting point 5.50DC, crymoopic conatant 5.12). A sample weighing 0.900 g was dissolved in 35.2 g of solvent and the freezing point d the solution was 4.30DC. Cdeulate the molecular weight. GATTON,G., AND KREBS,B., 2.Anorg. Allgem. Chem., 321, 148 (1963).
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1. In a. determination of the atomic weight of beryllium, 2.88408 g d BeC1. gave 10.34428 g of AgC1. Using the atomic weights of 107.880 for silver and 35.457 for chlorine, based on O = 16.0000, calculate the atomic weight of Be. Calculate the Literature Cited atomic weight of Be on the basis of carbon-12 using the atomic (1) BARROW, G. IM., "Physical Chemistry," MeGraw-Hill Book weight values of silver and chlorine from the most recent table Co., Inc., New York, 1961. available. Compare your calculated value with the value given (2) H ~ I L LW. , H., AND WILLIAMS,R. R., Jr., "Principles of T., Z. N a l u ) ~ in the table. HBNIGSCHMID, O., AND JOHANNGEN, Physical Chemistry," Prentice-Hall, Inc., Englewood forschung, 1, 650 (1946); cf. J . Am. Chm. Soe., 70, 3531 (1948). Cliffs, N. J.,1959. 2. Calculate the atomic weight of nitrogen from the follaw(3) MOORE,W. J., "Physi~alChemistry,'' 3rd ed., Prentice-Hall ing experimental results: N&Cl, 2.43720 g gave AgCl, 6.53011 Inc., Englewood Cliffs, N. J., 1962. g. Use the latest tablo of atomic weights based on earbon-12 for (41 W. F.. ''Physical Chemistrv." . . SAEEHAN. .. Allvn and Bacon. the values of the other elements. Compare the result of your calInc., ~ L s t o n 1'961. , ' culations with the value for nitrogen in the table. H ~ N ~ G ~ c H M ~ D , (5) MELLOR, J. W., "Modern Inorganic Chemistry," Longmans L., Z . Naturjom~hung, 1, 656 (1946); cf. O., AND GROALING, Green & Co., London, 1927. J . Am. Chem. Soe., 70, 3531 (1948). (6) P ~ I N G T OJN . R., , "A Text-Book of Inorganic Chemistry," 5th ed., MacMillan & Co., Ltd., London, 1937. Problems Based on Colligative Properties R. P., "Principle8 of Chemis(7) CRAW,L. H., AND GRAHAM, 1. Holmes and Forstner reacted PSClr with CHaNH2and try," Rinehart & Co., Inc., New York, 1955. (8) PAULING, L., "General Chemistry," 2nd ed., W. N. Freeman obtained an amorphous white solid whose elementary analysis was: C, 25.59%; H, 7.64%: N, 27.18%; P, 20.27% and S, & Co., San Francisco, 1958. 20.70%. The molecular weight was determined crymcopically (9) BROWN,T. L., "General Chemistry," Charles E. Merrill Books, Inc., Columbus, Ohio, 1963. in glacial acetic acid as 154.4. What is the formula of the
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