the visible light. This easy electron motion also makes magnetite a reasonably good electrical conductor, which is an undesirable property for practical applications in, for example, transformer cores. There other ferrites are used.
The Absorption of UV Light by Ozone SUBMITIED BY Edward Koubek US. Naval Academ)~ Annapolis. YO 21401 CHECKED BY
James 0. Glanvllle Virginla Tech Blacksburg,VA 24061 Figure 2. The effectofa magnet on slurries of Fe~O,(left)andof Fe20. as seen on the overhead projector.
have the inverse spinel structure with half of the B ions in the tetrahedral holes, B(AB)Oa. Magnetite is then properly written as Fe111(Fe11Fe111)04. At room temperature the compound is ferrimagnetic', with the moments in the tetrahedral interstices ordered antioarallel to those in the octahedral; see Figure 1. There results a permanent magnetic moment due to the iron(I1) . . ions. since the irou(II1) . . moments cancel. It is possible in a quite simple lecture demonstration to synthesize FeaO4 right before the students' eyes and to show its interaction with a magnetic field, comparing it to a paramagnetic material. For a sizable synthesis (which can be scaled up for very large classes), the following solutions are prepared: For mixture A: 100 mL of 0.1 M Fe3+ (ferric ammonium sulfate) 50 mL of 0.1 M Fez+(ferrousammonium sulfate) 250 mL of distilled water For mixture B: 150 mL of 0.1M Feat 250 mL of distilled water Mixtures A and B are made on thelecture bench, and then to each is added 75 mL of 1.0 M ammonium hydroxide. Mixture A gives a black precipitate of hydrous FejOa, while B gives the hydrous red-brown hematite, Fe203. A slurry of eachis poured intoa Petri dish, and the pair is placed side by side on an overhead projector; they appear as opaque, black circles. A small, strong permanent magnet is placed against the outside of each Petri dish. Soon a light spot develops in the dish with maenetite. shown in Fieure 2. as the solid is attracted to the m k n e t A d moves through the liquid phase. Clumns of solid are seen to accumulate near the ole faces. and streams of the oxide are seen to go toward them. After a while no more solid moves, but the light spot shows the depleted region near the pole faces quite clearly. The movement seen on the screen as the solid moves and the clear space develops is more dramatic than the static end result shown in Figure 2. No action isobserved in the dish rontaining the merely paramagnetic Fe203. Two further properties of the ferrimagnetic material can be discussed. The intense hlack color. comnared to the redbrown hematite, is characteristic of a mixed valent compound; very strong and broad charge-transfer hands due to easy electron hopping between Fez+ and Fe3+ ions absorb all
338
Journal of Chemical Education
With all the recent attention eiven to the ozone de~fetion problem in the popular press, tlhe Collowing demon&ation mav he of interest to vour students. It represents an extension of a demonstraiion published eariier by King and Templer.' Using a low-pressure mercury vapor UV lamp2 and a recentlv laundered white cotton sheet as a hackmound, one can produce a shadowgraph of ozone emerging f 6 m an &onator.3 The shadowgraph clearly demonstrates the UV-absorbing properties of ozone as may he seen in the figure. This demonstration is interesting in that it caualso lead to a discussion of fluorescence and the reason for addine a whitening agent to a detergent. Another interestine demonstration with this amaratus involved mercury vapor. A slight squeeze of a plastic bottle containine liauid mercurv ~roducesa " ~ u f f "of mercurv vapor as ashadowgraph. a his is an excellent demonstration to use to introduce the topic of atomic ahsor~tion. Caution: The toxicity bf 0 3 and Hg is well documented. Therefore these demonstrations should be carried out in well-ventilated areas. Care also should be taken with UV light to prevent eye damage.
'King, L. C.; Templer. A. D. Tested Demonstrations. 6th ed.; Division of Chemical Education: Easton, PA, 1965;p 219. A Model UVS-54, 254 mm Minerallamp available from UltraViolet Ploducts. Inc., San Gabriel. CA, is ideally suited for thls. This lamp uses a low-pressure mercury source. We use a homemade device similar to that described by Worstell. R. A. J. Chern. Educ. 1932, 9, 291.
Shadowgraph of ozone demonsbating its UV-abswbing properties
