edited by G E O R ~ EL. GILBERT Denisan University Granville. Ohio 43023
A Modification of the Copper Catalysis Demonstration Apparatus SUBMITTEO BY: Edwln S. Olson and R. E. Ashmore South Dama State Un vsrw, Brwkings. SD 57077 CHECKED BY: Darrell D. Axtell Eastern Montana College
shown to undergo a similar oxidation if the alcohol is heated in the water bath to within lo0 of its boiling point. These other alcohols have more of a tendency to "pop" especially if you try to test the effluent gases, thus testing the oxidation product from alcohols other than methanol should he done with extreme caution. With methanol, use care in bubbling gases through the concentrated HqSOa - .solutions. and take care not t o inrale the formaldehyde or methanol vapors. Never use oxygen gas, only air. ~~~
Billings, MT 59101
The demonstration reported by one of us several years ago has been used successfullv in introducina and illnstratine the oxidation of alcohols to carbonyl comp&nds over a copper catalyst.' We should like to suggest amodification in the ap. paratus which gets a little more out of the demonstration. If the reaction chamber is constructed with a constricted neck 4 cm from the top, the Nichrome holder for the copper coil can rest there, and then a rubber stopper with a lead out tube can he inserted in the top after the reaction has started. Thus, the effluent gaseous products can be huhhled into tuhes containing testing reagents.
~~~~
' Ashmore, R. E., J. CHEM.EDUC.,45,243 (1968).
Feigl. F.. "Spot Tests in Organic Analysis," Elsevier, New York, 1966. 0. 434. ~ k n e rR. , L., Fuson. R. C.. and Curtin, D. Y.. T h e Systematic
ldentificat~on of Organic Compounds," 5th Ed., John Wiley and Sons, York,19649 P. 126.
Lecture Experiments in Gas-Liquid Chromatography with a Simple Gas Chromatograph at Room Temperature m
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e
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Adalbert Wollrab Institute Didaktik der Chemie at the Justus Llebig University 63 Giessen Federal Republlc of Gwmany
TO TEST N E E
arorm 8":
Rlchard R. Doyle Denison University Granville.OH 43023 ..
A thick-walled mhher tube isconnected with one end to the outlet of a reduction valve which reaulates the flow of hvdrogen from agas cylinder. The othe'end of the rubber tuge is connected to a glass tube (about 30 in. long and 'Izin. diameter) filled with salt which is coated with a layer of hexadecane. A short glass tube, drawn out a t one end into a c a ~ i l lary (inner diameter about 1 mm) bent up at a right ang];, is joined by a short rubber connection to the glass tube packed with salt.
,, TO BUBBLER
Copper catalysis apparatus. Thus, one can show that the product of the copper-catalyzed oxidation of methanol is indeed formaldehyde by the specific chromotropic acid test and simultaneously exhibit some chemical properties of formaldehvde. T o test for foimaldehyde, the gases are huhhled into concentrated sulfuric acid for about half a minute and then a few milligrams of c~romotropicacid are added, Formaldehyde forms a violet dye with chromotropic acid2Another good test is t o bubble the gases into 2,4-dinitro~henylhydrazine reagent.3 The yellow precipitate of the 2,4-dinitrophenylhydrazone is formed. After arousing interest with these colorful demonstrations, the nature of the condensation of formaldehvde with Dhenolics (such as chromotrooic acid) and ~~~~~~, ~with -.-~ hydiazines can he developed in the lecture in addition to a discussion of the oxidation. Other volatile alcohols (ethyl, propyl, isopropyl) can be a
1042
Journal of Chemical Education
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Coating o f t h e Salt and Packing 0' the Column Material: one 250-ml beaker, 1Petri dish (10-15 in. in diameter), 1mortar, 1spatula, 1glass tube (about 30 in. long and 'h in. diameter), cotton wool, 100gsodium chloride, 1.5 ml hexadecane, 30 ml chloroform. Procedure: 100 g sodium chloride is ground in a mortar in 10 g portions to a very fine powder. 1.5 g of hexadecane is mixed with 30 ml chloroform and the liquid poured onto the sodium chloride in a 250.ml beaker. ~h~ salt is thoroughly mixed with the liquid and placed in alarge Petri dish. The mixture is stirred and blended with a spatula in the fume cupboard until the saltlwks dry and is no longer lumpy. The dish is left 2 hr in the fume cupboard. The glass tube is clased with a wad of cotton wool at one end and filled with the coated ~ salt ~ by means ofafunnel connected to theelass - tube hvambber tube
' Wollrab, A., J. CHEM.Eouc. 52,200 (1975).
joint. In doing so the class tube may b~ l~ahtlytapped on a ruhher surface roarhieve a firmer parking. After filling thc glass t u h its ~ other end is also provided with a wad of ~trttonwu01, SO thaT the material cannot drop out,
in aminimum amount of HN03 (-1% ml of 15M). A magnetic stirrer is helpful but not essential. Then add solid NaC2Ha02(-2 g), with stirring, until the AgaAs04reprecipitates. The addition of nitric acid, followed by sodium acetate, can he repeated several times.
Experlments
Procedure B-Silver Phosphate Dissolve 1.9 g (5 mmoles) Na3POa.12HzO in 200ml Hz0 and proceed as in Procedure A. Silver ohosnhate is lemon vellow and will he less easilv seen in a lame leetuie hail than will silver arsenate. How~, ever, it hszardow uasw dispusal prrsmu a problem, thm phwphau' is the sysrem of choice. A magnetic stirrer is helpful for rliswlving s i h r phosphate in nitric a r d Allow 1'2 2 ml of 15 .\I HNOIand vigorous stirring.
Separation of a Pentanel Hexane Mixture. Material: the apparatus, 1hypodermic syringe (entire volume 1-2 ml), pentane and hexane. Procedure: The hydrogen flow rate is regulated at the reduction valve within the range 150-200 mllmin. The hydrogen is lit at the outlet of the capillary. The flame usually reaches a height of 11, in. A hypodermic syringe filled with 0.1 ml pentanelherane mixture (1:4 by vol.) is injected into the thick rubber tube, so that the needle punctures the tube close to the opening of the glass tube. The efflux of pentane and hexane after completed separation enlarges and intensifies the flame. The flame can be seen particularly well in a darkened room. Separation of a Methylene ChloridelChloroformlCarbon Tetrachloride Mixture Material: the apparatus, 1 hypodermic syringe (5 ml by vol) 1 copper wire 1%in. long, 1nail, methylene chloride, chloroform, and carbon tetrachloride. Procedure: The hydrogen flow is regulated within the range 200-220 mllmin. A short copper spiral is made by coiling a copper wire round a nail. The copper spiral is set over We end of the capillary. The hydrogen is lit and the end of the copper wire is bent into the flame and serves to identify chlorine-containing compounds in the flame. A 5-ml hypodermic syringe is filled from the vapor over the liquids (not the liquids themselves!) with 0.3 ml methylene chloride gas, 1 ml chloroform gas, and 1.5 ml carbon tetrachloride gas. The gas mixture is then injected into the vacuum tube. Theeffluxof the components is recognizable by the green coloring of the flame.
Equilibria in the Silver Arsenate-Arsenic Acid and Silver Phosphate-Phosphoric Acid Systems
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Hazards and Disposal: Arsenate-containing compounds are highly poisonous and should n o t b e ingested n o r allowed to come i n contact w i t h mucous membranes o r skin. The arsenate mixture from Procedure A should he disoosed of accordine to the hazardous waste procedures used at the reader's institution. Donot disposeof it down thcdrain! If noacceptable method of disposing t ~ arsmutes f is availal~lr,use Procedure R. The mixturr resultine from Procedure H ran he flushed down the drain with plen& of water.
Discussion This demonstration can be used to illustrate relative strengths of acids, p H effects on solubility, and, t o some extent, periodic relationships. Chemical equations for the arsenate and phosphate systems are as follows: X=As,P
+
3Ag+(aq) HzxO~-(aq)= AgaXO,(s)
-
+ 2Hf(aq)
AgaXOds) +excess H+(aq) HaXOr(aq) + 3Agc(aq) 3Ag+(aq)+ HsXOdaq) + excess NaCzHaOz(s) Ag&Oa(s) + 3CzHaOzH(aq) + Na+(aq) CzH30z'(aq). Pertinent equilibrium constants for the two systems are displayed below:
-
+
SIBUrnED 8":
Patricia L. Samuel Boston University Boston, MA 02215
Substance
&q
K1 s.7.52 X K2 16.23 X
HsPOI'
Ks
C m m sr:
= 2.2
X
lo-" 10-19
George Virtes Ward Melville High Schaol Setaukel, NY A qualitative test for arsenate ion' provides the basis for a colorful demonstration of the principles of relative acid strength, solubility product, and effect of p H on solubility. Silver arsenate, a chocolate brown solid, is formed by mixing aqueous solutions of silver nitrate and potassium arsenate. T h e ~reciuitawis then dissolved with nitric acid. Addition of solidsodLm acetate causes silver arsenate to reprecipitate. Phosphate can be substituted for =senate;= lemon-yellow s i l ~ e ; ~ h o s ~ h aist ethe precipitate. Materials 1-1Erlenmeyer flask HNOs 15 M AgN03,O.l M KH2As04,or other arsenate salt (Procedure A) NaaPOp.IZHz0, or other phosphate salt (Procedure B) NaCeH201. - " -. solid medicine dropper or disposable pipette spatula magnetie stirrer (optional) Procedure A-Sliver Arsenate Uirrrrlve 0.0 6 I3 mmoles~KH2As04in ?UO ml distilled w e e r in a 1-1 Erlenmeyer flask. To this solut~onadd 20 ml of u.1 M AgN03. Chwdate brown Ac3ArOr will precipitate. 1)issolre thp precipitate
~.
A&ASO~"
K,
= 1.08 X
'"Handbook of Chemistry and Physics". 6lDted.. CRC Press. 1980-81. Llnke. N. F. and Seidell. A,. "Solubilitiesof lnaganic and ~etal-organic Compaunde." 4m ed., american Chemical Sociew,1958.
Silver phosphate and silver arsenate are typical salts of weak acids and thus dissolve in acidic solution. Since acetate ion is a stronger base for protons than either dihydrogen phosphate or dihydrogen amenate, addition of sodium acetate to these solutions results in the formation of acetic acid: HsXOdaq) + CzH30z-(aq) * CzHaOzH(aq) + HzXOh-(aq) The conjugate bases of phosphoric and arsenic acids dissociate to phosphate and arsenate, allowing the reprecipitation of the silver salts. Periodic relationships between structure and acid strength
Presented in part at the Forum on General Chemisby. Colorado School of Mines. June 5 and 6. 1961. Sorum. C. H. and Lagowski, J. J.. "introduction to Semimicro Qualitative Analysis," 5th ed.. Prentice-Hall, Inc.. 1977. Hufstedler. R. S., Virginia Wesleyan College, Norfolk, VA, private communication. ~
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Volume 59
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Number 12 December 1982
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