Modeling hypersaline lake "turn-over"

Modeling Hypersaline Lake "Turn-Over" For the past ten years, Beientistr have studied the Dead Seaas it approached and then actually "tumed-over"orphysidy inverted itself, mixing a more dense saline water with less dense water heneath.' Several articles may come to mind where aerial photographs have shown a saline lake forming a solid layer of salt on its surface only to have that layer invert and fall to the lake bottom. While experimenting with salt solutions to he used in a high school chemistry soap-producing experiment. a method was discovered that models saline lake invenions. 1)escribed helow is the procedure for cmstrucfing this model and some preliminary findings. Variations on the technique or equipment certainly may prow uscfu1, hut the fullouing worked sat~~

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Procedure: Add approximately 2 1of saturated salt solution to a 3-1 heaker. Place the beaker on a stirring hot plate, and add a magnetic stirring bar to the salt solution. Stir the solution a t low speed and have.the heat on a low-medium settine. " In a few hours the evaporation from the surface without t h ~ accompanying convection currenu (the stirrer breaks up the currents) will allow solid salt tu form on the surface. As the density of the surface continues to increase due to further evaporation of water of crystallization from the salt layer, the layer eventuallv becomes too heaw and a break-un oroeeeds uncl the layer has been displaced to the bottom of the beaker. At this time a new layer d lbegin to form on the surface of the saline solution. The photographs show the break-up of the surface!saltlayer at two different times. Note that several layers have already been deposited on the bottom of the beaker. Preliminary findings show that the solid salt layer can w i l y reach 1 cm in thickness. An analysis on the salt layer shows an approximate formula of NaC1.4Hz0 a n d a density of 1.6 glcms. The underlying salt solution has a density of 1.2 gl cma. ~~~~

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' Steinhorn, I., and Assaf, G., Science, 55 (October 5,1979);Steinhorn, I., and Gat, J., Sci. Arne?., 102 (October 1983). Gary Sprague MBdtwd Senior High School Medford. OR 97504

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Journal of Chemical Education