edned by
GEORGE L. GILBERT Denison University Granville, Ohio 43023
Paramagnetic Properties of Fe(ll) and Fe(lllj Submitted by: Checked by:
Nooiin Walker Pensacola ~ u n i o College r Pensacola. Florida 32504 Erwin Boschmann I U - P U a t Indianapolis Indianapolis, Indiana
gand Field Theory, can be developed with its weak field-high spin and strong field-low spin concepts. The basic demonstration can he used to suggest additional questions and activities. Do all metallic ions have paramagnetic characteristics? Should we expect elemental metals to exhibit paramagnetic praperties? Do all ligands force electron pairing? Can water of hydration he distinguished from aquo complexes by differencesin the paramagnetic properties?
Preparation Obtain a small amount of powdered Fe2(S0J3, FeSOa, K 3 F e ( C N ) ~and KaFe(CN)G, four 7 X 25-mm test tuhes, The Preparation of Polyurethane Foam: lightweight twine, and a strong magnet of about 45 lh. pull A Lecture Demonstration such as a single pole of Edmund's No. 70572 (protect your watch). Suspend a test tuhe ahout one-quarter filled with Submitted by: Glen E. Dirreen powdered Fe2(S04)3 by a piece of twine approximately 35 cm a n d Bassam Z. Shakhashiri long. Repeat the same for powdered FeS04, for K ~ F ~ ( C N ) G , University of Wisconsin-Madison and for K4Fe(CN)~. Checked by: Leonard C. Grotz, Demonstration Uniuersity of Wisconsin- Waukesha, When each of the test tuhes is hanging motionless, test the Waukesha. 53186 F e ~ ( s 0with ~ ) ~the magnet; the tuhe is attracted vigorously. A polyurethane foam is produced by forming a polyureRepeat the test with each of the other three test tuhes. One thane polymer concurrently with a gas evolution ~rocess.1The finds that FeS04 is also attracted vigorously; the K3Fe(CN)~ polymer is formed by the reaction of a polykther polyol, is attracted less vigorously; and the K$e(CN)$ is unaffectHO-R-OH (molecular weight range 400-4000), with a polyed. functional isocyanate, OCN-R-NCO, in the presence of triRemarks chlorofluoromethane as a blowing agent. The reaction may he represented as Numerous students have the misconception that compounds do not have magnetic properties: iron is magnetic, hut H 0 iron compounds are not. This series of testa is designed to I II correct the misconception by demonstrating the existence of -R-OH + -RNCO R-N-C-O-Rparamagnetic properties among iron compounds. AdditionThe polyfunctional character of the reactants results in a high ally, by showing the absence of paramagnetic properties in degree of cross-linking in the product, forming a rigid foam. certain iron compounds, the opportunity is provided to exWe have had excellent success with a two component ureplore the pairing phenomena of 3d electrons. thane foam s y ~ t e mComponent .~ numher 30-1961, light amber The test with Fe2(S0J3 demonstrates the observable in color, contains a polyether polyol, a blowing agent, a silicone paramagnetic properties attributable to the five unpaired 3d surfactant, and a catalyst (usually an amine or a tin(I1) organic electrons. The subsequent test with FeS04 shows that parcompound). Number 30-2023,which is dark in color, contains amagnetism is also a predictable property of Fe(I1) due to its a polyfunctional isocyanate. Both components are viscous. four unpaired 3d electrons. (Should one expect to observe a quantitative difference between the paramagnetisms of Fe(I1) Demonstration and Fe(III)?) The test with the complex K3Fe(CN)6 again demonstrates Isocyanates are toxic; care should be taken to avoid skin conthe presence of paramagnetic properties although they are tact and to provide adequate en ti la ti on.^ This demonstration significantly less than the two previous simple salts. (Doesthe should be performed in a properly operating hood; some indecrease indicate a fewer number of unpaired 3d electrons?) dividuals may develop a severe asthmatic reaction upon The fourth test, that of K4Fe(CN)e, results in no observable breathing minute amounts of phenyl isocyanate which may be paramagnetism; the complexed Fe(I1) has no unpaired 3d present along with the polyfunctionali~ocyanates.~ electrons. Where did they go? Two explanations can he developed to account for the difPlaceahout 10 ml of no. 30.1961 in a heaker or a paper cup. ferences between the iron complexes and the iron salts, and Add 40 ml of the isocvanate (no. 30.20231 and stir ihe \i.SCIIUS between the comolexes themselves. Denendine unon the somixture well with a glass rod. Within one minute of stirring phisticatiun of thestudenu, theattractit,ely simplistic Valence the oolvurethane heains to form and the Freon-orooellant . . . . Rond Theory can be exolored utilizine the conceDts of coorcauses a volume increase which is usually complete in ahuur dination numbers, unoc&upiedo r b i t a l h d hyhrikzation. For t w ) minutes. The volume will increase 20 3U times that of the other students, the more contemporary explanation, the Lioriginal mixture. The polyurethane foam assumes the shape
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Volume 54, Number 7, July 1977 / 431
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of the container in which it is nrenared. . The freshlv..n r e.~ a r e d foam usually contains unreacted isocyanate and should not he handled until it has cured several hours in a well ventilated area. The individual components are soluble in acetone and may he cleaned up easily. However, fully cured polyurethane is only slowly soluble in such solvents as dimethylformamide. It is therefore best to work with disposable surfaces. A dramatic demonstration can be performed in a 1-1tallform beaker. Mix the two components (100 ml each) and stir. If carefully supported by two glass rods, the foam can he made to form a column a t least twice the height of the beaker. Small amounts of a food coloring dye can be added to component no. 30-1961 prior to mixing with the other component. Thus, foams of different colors can he prepared. ~~~
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Figure 1.
Electrolytic-fuel cell.
'Saunders, K. J., "Organic Polymer Chemistry,'. Chapman and Hall, London, 1973, pages 318-46. 2Number 30-1961130-2023 available from Freeman Chemical Corporation, P.O. Box 247, Port Washington, Wisconsin 53074. Minimum order of $25 purchases one gallon of each component. 3Hocking,M. B., and Rayner Canham, G. W., J. CHEM. EDUC., 51, A580 (1974). 'Gilbert, G. L., private communication (1976).
The Electrolysis of Water-Fuel Submitted by: Checked by:
Cell Reactions
H. I. Feinstein a n d Vernon Gale George Mason University Fairfax, Virginia 22030 Becky J. Hickey Uniuersity of Washington Seattle, 98100
An apparatus has previously been described1 in which the polarization current of a water electrolytic cell is used to activate a flashliaht bulb. The amaratus of Humbv has now been modified that a light emitting diode or asmall electric motor may be powered by the counter emf. The counter emf in this case may also be looked upon as the product of a HZ-O2 fuel cell. Figure 1shows the complete apparatus. The binding posts labeled PROBES are used to connect the apparatus to an electrolytic cell (about 1M sulfuric acid) via carbon electrodes. The binding posts labeled MOTOR are used to connect the cell to a small toy d.c. motor. The switch labeled L.E.D. (light emitting diode)/MOTOR is used to select the load to be applied to the cell. The switch labeled CHARGEDISCHARGE is used to charge the cell or to discharge it into the load. Figure 2 is a view of the open case. Figure 3 is a schematic electronic circuit diagram. In the CHARGE nosition, enoueh hvdroeen and oxvaen will accumulate so t h a t when the D~SCHARGEposit& is selected the L.E.D. will glow or the motor armature will begin to revolve, as a function of the L.E.D./MOTOR switch position. The cycle may be repeated indefinitely. This demonstration illustrates the electrolysis of water and its reverse reaction-the H2-02 fuel cell without the added expense and inconvenience of using external sources of hydrogen and oxygen. The parts should cost no more than $10.
Figure 2 ,
view of circuit cell
CHARGE MOTOR
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i 3. ~schematic ~ ~electronic e circuit diagram of cell.
Parts List Suggested Sources
Jumper leads with alligator clips SPDT switches Binding posts Binding posts 1 100-ohm 'h watt resistor 1 Clip 1 LED
2 2 2 2
1 Plastic case 4" X 2 V X
'Humby, S. R., in "The Science Masters' Book, Series 1,Part 1, Physics," (Editor: Adlam, G. H. J.), John Murray, London, 1931, p. 177.
432 / Journal of Chemical Education
1W
Lafayette 99 R 00572 Lafayette 99 F 61897 Lafayette 32 F 64603 Lafayette 32 F 64611 Lafayette 52 F 2049 Lafayette 99 F 62879 Hewlett-Packard 50824655
Kelvin 133-58 1 Toy motor Edmund P-60985 1 9 V transistor radio battery 2 Carbon electrodes, beaker, acid, stand
