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Optical Projection Experiments to Demonstrate New Curricula Contents Ivo Perina University of Zagreb, P.O. Box 153, 41001 Zagreb, Yugoslavia
Demonstration of experiments by optical projection compared with classic demonstration of experiments has a number of advantages: Visual clarity is increased. Enlargement of the experiment facilitates easier detection of details. Semi-mieratechnique experiments save on use of chemicals. Little danger is involved either for those who perform the experiments or for the students. By switehingoff the device studentsare visually excluded from the chemical nrocess. enabling the teacher to proceed with the work in the ciassrook, without the student's attention being concentrated on the experiment only. I n literature ( 1 4 ) t h e experiments described, using this technique, are mainly from general chemistry, inorganic, analytical, a n d physical chemistry. Experiments i n organic chemistrv have been described far less. while exneriments from biochemistry a n d ecological chemistry have been almost ignored. Therefore, in our methodological research, we directed our attention toward t h e development of experiments in those fields. I n some demonstrations safety aopales .. . .should he worn a t all times.
The reaction equation
C6Hl, + Br,
light
C6Hl,Br
+ HBr
This experiment has been described previously in the literature (5) hut not utilizing a projection technique. Warning: Wear
rubber gloves, and have handya bottle of glycerol. The Reactivity of a Homologous Series of Saturated Monovalent Alcohols
This experiment is carried out with the help of an overhead projector. On the working surface of the overhead projector Lay a transparency in order to save the projector. Five Petri dishes (5-10 cm in diameter) are placed on the working surface, and 3 4 mL of different anhydrous alcohols are poured into the Petri dishes: methanol, ethanol, 1-propanol, 1-butanol, and 1-pentanol. Place a very small piece (like a grain of wheat) of purified dried sodium in each sample. Cover Petri dishes with glass plates. The reactions can he observed on the screen. The reaction is more vieorous for alcohols with fewer carbon atoms. Therefore. it is useful demonsrrnting the relative reactivity of the hornoh,gous aeriesofalcohda. Warning: Wear safety gogglesat all times.
Experiments The Substitution of Saturated Hydrocarbons
Fill a glass cuvette with 10 mL n-hexane (automobile gasoline can also be used if previously purified hy removing unsaturated hydrocarbon with concentrated sulfuric acid), and gradually add 10 drops of bromine. When placed on the device, theoptical bench (Fie. ,. 1). . the bulb orovides enough .. lieht ,. and heat needed for the renrtim. M'lthin 1-2 min thecdor of the bruminedisnpprarr and the fmnntmn uf gas bulhlei can bc seen in the srrern. The ncid~r nature of the resulting hgdruycn brwnide can be seen bv placing a moistened piece of universal indicator paper at the cuvette opening.
Figure 1. Optical bench with additional mirrors: A = Cwene. and B. B = Minor system. 344
Journal of Chemical Education
The Quantitative Determination of Hydrogen Formed in Reaction between Anhydrous Ethanoland Sodium
Assemble a device according to Fiwre 2. On a special transparency draw the rcnle of the syringe leg.. from 0-50 mL1 Stick a prpceof wire trhaped like L)at theend of rhe piston, and put it to
Figure 2. An assembly for measuring gas volume available for optical projection: A = Working surfaceof the ovehead projector, B = Syringe. C = Scale of syringe on the transparency,and D = Pointer.
the zero mark on the transparency (67).Then place the weighed piece of purified and dried sodium (like a grain of wheat) into a suction tube and the determined quantity of anhydrous ethanol is added from a funnel drop by drop until all sodium reacts. The formed hydrogen exerts the pressure on the piston, and the volume of released hydrogen can he read on the scale at the screen. The suction tuhe, which serves as a reaction vessel, is not projected on the screen, hut only the process of collection of hydrogen in the syringe. By simplified numerical reduction to standard conditions students can learn that sodium forces out only hydrogen from the hydraxyl group. This data should be sufficient for students to deduce the structural formula of ethanol and reaction yield. Warning: Wear safety goggles.
The Enzymatic Degradation of Hydrogen Peroxide by < Catalase A device similar to the one in the previous experiment is assembled. In this experiment, however, a funnel is not required. Hydrogen peroxide (5 mL, w = 3%) as a substrate and 5 mL of fresh juice obtained from grated potatoes, which serves as a source of catalysis enzyme (catalase), are placed in the reaction vessel. (Neither here nor in other enzymatic experiments can the enzyme activity he predicted and quantitatively expressed, as they depend an a whole series of factors, primarily on the biological source. Therefore, the demonstrator must check the experiment prior to the demonstration and then adjust the above-quoted approximate quantity of enzyme to the conditions of the experiment). In the vigorous reaction, under catalytic influence of catalase, oxygen develops which exerts the pressure on the piston. Volume of the released oxygen can be read a t the screen:
The Effect of an Activator and Inhibitor on Amylase Activity ( Put n euvette with three cells on ootieal hench and add 1mL of larch s o l u t ~ m( w = O.Sccr into each cell a substrate Then add 2 ml. of enrymatiz preparation of amylase in enrhcell.'l'h~fnllowing can he " t i l i d na a wurccof enzyme: saliva, extract ofgerminated barley in water, commercial enzyme or a paucreatin preparation containing amylase, lipase, and peptidase. Pancreatin tablets (4) were dispersed in distilled water (20 mL). The dispersion was passed through a filter. The filtrate served as a source of enzyme. Put 1 drop of Lugol's solution (2 g KI in 300 mL of distilled water with 1g of elementary iodine added) in each cell. This causes a dark hlue coloring in the cells. Finally, add 1mL of distilled water in the first cell, 1mL of sodium chloride solution (w = 1%)in the second cell, and 1mL of eopper(I1) sulfate (w = 1%)in the third eell. In the enn)matic reaction starch hreakr up into fragments which do nut r d m nith 1.11gol'savlution. The sequence of discolurinr is os t'dluws firit the cell with sodium chlmde (chlorides are k v a t a r s of amvlase). followed bv the cell with the distilled walrr.'l'he cell with mppertll, polfate beromrs only slightly disrulnred or not at all, becausr hem y metals are mhibitors crf amylase. ~
The Effect of a Substrate Concentration upon the Speed of an Enzymatic Reaction A ru\ette with three cells id required and in sequence 3 mL of urea solution oidifferent rrnwentratim wadded \t..g., u = ZOi, ;I"i, and5?~.dissolvedin . vhus~hote buffer DH = 7 tr = 0.2 moldm-'I. . Three &illiliters of enzvmatie urease oreoaration should then be added in each. A source of this enzvme can be found in eommerrial w e m e , fresh extract ds
