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
