edited bv GEORGE
L. GILBER;
Denison University Granville. Ohio 43023
Partition Coefficients-A Lecture Demonstration Thomas A. Newton Colby College Watervilie. ME
put, or clamped if possible, onto the projedor. Nails have been pounded into the piece of wood t o act as dense nuclei. A student is then asked to roll slowly some metal beads of about 1.5 cm diameter through the tunnel. On the screen, all the students can see very clearly the paths taken by the beads before entering and after leaving the tunnel. The students are asked to explain why some beads are deflected or rebounded.
CHECKED BY
Richard F. Jones Sinclair Community College Dayton, OH
The extraction of aqueous solutions of indophenol and its sodium salt (or their 2,6-dichloro derivatives) with carbon tetrachloride and chloroform provides a convenient illustration of the concept of partition coefficients. At 10-3M in water indophenol is burgundy, and extraction with CCl4 (e = 2.24) affords a yellow-orange organic layer which is lighter in color than the red aqueous phase. When the more polar solvent CHCL " (6. = 4.81) is used. more of the nhenol is removedfrom the water and the p a t t e k is reversed: the organic phase becomes orange-red and much darker than the water layer which turns pink. Alternatively, a CCl4 extract of a M aqueous solution of the sodium salt of indophenol is light yellow, paler than a CCld extract of the less polar, un-ionized compound. The same concent has been demonstrated using 12 in a three layer system of C C ~water , and ether.' The solutions necessary for the demonstration can be prepared easily and in dramatic fashion in front of a class by sprinkling 0.05 g of the sodium salt onto the surface of 200 ml of water in a 250-ml Erlenmeyer flask. Beautiful deep blue streamers gmw gracefully downward marking the paths of the dissolving particles as they sink slowly toward the bottom. After gentle swirling, a 25-ml aliquot is removed and the remaining solution is transformed from blue to burgundy by the addition of 2 drops of 6 N HC1. The demonstration is completed by extracting 25 ml of the desired aqueous solutions with equal volumes of CC4 or CHCI3and draining the layers into 20 X 150 mm test tubes for comparison. ~
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Summerlin. L. E.. "Polar Properties and Solubility," in "Tested Demonstrations in Chemistry," 6th Ed., J. C m . Ewc.. Easton, PA. 1965,223.
A Simulation of Rutherford Experiment Kit-Tai Hau Leung Shek Chew College 80 Hi" Kwong St. SBU Ma" Ping Hong Kong
Except for the one or two experiments on the cathode ray tube, the teaching of atomic structure is often chalk and talk. The demonstration described below simulates the Rutherford Model and provides an analogy which links the model to the students' experience in playing with marbles. I t arouses the students' interest to think in the way Rutherford did in 1906. The demonstration is carried out on an overhead projector. A piece of wood 34 X 8 cm with two stands about 2 cm high is
It is found that the demonstration works better with heavy beads. Metal beads and glass marbles are better than plastic ones. Beads with holes will not work. A large, plastic drinking straw is sliced longitudinally into halves and is used as a track in rolling the beads (see diagram). A cardboard frame as big as the projector surface is used t o prevent the beads from falling off the projector. With the use of different protrusions underneath the wood, the students can be asked to determine the shape or character of the object from the manner in which the deflection of the beads occurs. Different atomic models can he simulated through the use of different protrusions. The following are some suggestions: Protrusions
Effect
occasinal deflections beads (metal)disappear in the magnets tunnel approx. half bf the beads are 3) nails at 2d apart deflected d = diameter of beads 4) nails on the riebt-hand side all beads on the rizht-hand side rebound all the beads rebound 5) a rubber hand across the tunnel 8
2 or 3 nails
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Oxidation by Mnz07: An Impressive Demonstration of the Powerful Oxidizing Property of Dimanganeseheptoxide Klaus R. Koch Depmment of Analytical Science P.D. Hahn Building University of Cape Town Private Bag Rondebosch 7700 Cape Town. Republic of South Africa CHECKED BY
Paul F. Krause University of Central Arkansas Conway. AR 72032
The known oxidation states of manganese range from -3 to +7; those most commonly encountered are +2. +4, and +7 ( I ) . The powerful oxidizing properties of the Mn04- anion are well known and enjoy widespread chemical application. There Volume 59 Number 11 November 1982
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