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GEORGEL. GILBERT Denison University Granville. Ohio 43023
Densities and Miscibilities of Liquids and Liquid Mixtures
discuasion of solubility and liquid miscibility. The organic liquids combine into one phase having an average denaity that may he calculated and is slightly Less than 1.00 glmL.
SVSMlTTED BY
Davld A. Franz Lycomlng College Wllllamspnt, PA 17701 CHECKEDs~
Davld Speckhard L O ~ College S
Dubuaue. IA 52001
he following sequence of demonstrations is quick, easy to perform, and lends itself to quantitative calculations. The first four demonstrations, although simple, provide important illustrations of the concepts of mass and density. The suggested quantities should he used to ensure success of the last four demonstrations of miscibility and average density, which prove to be surprising, thought-provoking, and visually interesting. Materials HzO; CHlClz (caution: toxic); petroleum ether (60-90 'C) or hexanes or ligroin (90-120 "C) (caution: flammable liquids); four 100-mLgraduated cylinders; two 250-mL graduated cylinders; food dye; stirring rod with plunger end (14-16 in. long); balance (electronic pan balance recommended).
Density of CHZCI, Tare a 100-mL graduated cylinder, then add about 20 mL of CHC12. From net volume and mass, calculate the density (1.3 gl mL). Add more CHC12to a final volume of about 35 mL. Ask dass to calculate new total mass, using previously determined density. Compare calculated mass to observed mass. This is also a good opportunity to apply the concept of significant figures. Density of Hz0 Tare a second 100-mI, graduated cylinder. Add about 60 mL Hz0 and two drops of food dye. Determine density from ohserved mass and volume (1.0 g/mL). Density vs. h4ass After asking the class which is heavier and which is denser, pour the CHpCLzand H20 into a 250-mL graduated cylinder. Colored water layer floats, even though it is heavier. Densities of Petroleum Ether and Water Repeat steps 1-3 using two more graduated cylinders and 45 mL of pet. ether ( d , 0.64 g,mLj or ligroin (d,0 74 gtm1.l or hexanes ( d , 0.66 ym1.1 m one cylinder and 45 mL water in the other cylinder. Combine these two liquids into the second 250-mL cylinder, causing the organic phase to float on the water phase. Combined Liquids Carefully pour the contents of the pet. etherlwater cylinder into the water/CHzCIz cylinder. Three layers will result, with the pet. ether on the top, colored water in center, and CHGB on bottom. Liquid Miscibility and "Average Density" First. ask the class what will haonen when the three liauids are nnnred'into the other 250-mL evfinder and which will b; on too. r..~--~~ Then, very unrorefull), pour the contents into the other cylinder. It m a y rcquire two sr three rransfers to achieve the desired miring. Result is two liquidlayers with the water on the bottom. This result is totally unexpected by students, and can prompt an interesting ~~~~~
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Journal of Chemical Education
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Increasing the Average Density of the Organic Phase By slowly adding more CHCI?, the average density ofthe organic phave can be increased, causing the layer to sink through th? water. Incomplete mining, however, cnuaea the rising water layer to i d a t e a section of less-denseorganic phase on top, producing three liquid layers once again. Thorough mixing or pouring of all contents into another cylinder will produce two layers, with the water now on top. (Also of interest, but not V e N visible, is the observation that the meniscus at the water/organ$ interface curves up into the water layer.) Decreasing the Average Density of the Organic Phase By adding more pet. ether and stirring it to the bottom to ensure mixing, it is possible to form an organic phase with an average density equal to that of water. The result is the formation of colored water globules dispersed throughout the organic phase. Pouring in more CHzCLzat this point causes the water to rise to the top, creating a visually interesting effect. Cleanup The aqueous layer is easily siphoned off and may be discarded. The CH2C1zmay he reclaimed by simple distillationfrom the organic phase or else dealt with as waste halogenated solvent.
A Lighted Stage for Use in Chemistry Demonstrations S U-B M ~- E-BY O
Blorn Olesen and Lestar L. Leaton Southead M10.0url State Unlversny Cape Glrardeau, MO 63701 CHECKED BY
Paul F. Krause Unlverdty ol Central Arkansas Canwav. AR 72032
~ h i one n of the authors (LL) started teaching in 1951, he soon added the use of demonstrations to his lecrures. Shortly after that he added a lighted stage (homemade) to enhance the colors of the solutions. Over t h e vears, he has desiened and made (or had made) several of theselighted s t a g s of various sizes and utilizing different light sources. During the summer of 1985 the authors held a workshop for area high school chemistry teachers. Utilizing a Bright-Stik*, they designed and built a lighted stage for each of the attending teachers (see figure). This stage bas been used now for five years, including the many demonstrations (more than 100) in the outreach program of our department. Some of the favorable features of this stage are: 1. The size makes it easy to transport and store. (It can even be
stored on end.) 2. The 20-W bulb emits the right quantity of light, so there is no need for frosting or painting the glass. 3. The length is sufficientto support six beakers at a time (enough for Bill Hutton's rainbow demo). 4. The 20-W bulb does not generate enough heat to cause any nrohlems. 5. '['he d e s w has been sent to other school^, where the atnnds have been constructed without difficulty. 6. Thestand is atal>leenoughrostnnd 01,end, so you may backlight graduated cylinders. 7. The materials for the stand can he purchased for $20.
