A Convenient Melting/Freezing Point Depression Apparatus Conventional meltinglfrre7ing point dcprea.~h,nappnrnttrReause mercury thrrmomewrv with p.radunt~on~of 0.l0C. Studenwmnrjrtentlg complam nhouc their inability to perform the experiment accurately and easily, because the thermometers are particularly difficult to read. To overcome this problem we have built an apparatus that incorporates an easy to read, moderately . priced . digital thermo&er. The auuaratus pictured (Fig. 1) utilizes an Analog Devices AC2626K. 6-in. stainless steel temperature proge. housed in a toolednylon rod which centers the temperature probe, holds it in the same position for each experiment, and serves as a guide for the stirring wire. The response time of the probe is 2 sec. The probe is attached to an Optoelectronics TRMS:SOW 4% digit mul-
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There are numerous advantages ta using this apparatus. The TRMS:SOW displays the temperature in % in. digits to O.Ol°C, eliminating the guesswork involved in reading mercury thermometers. The probe is able to withstand far rougher handling than the norinal apparatus, because it is made out of nonfragile materials. The dangers associated with the breakage of mercury thermometers are also eliminated. An added advantage of the TRMS:5000 is that, as a multimeter, it can be adapted to other uses in the lab. ! Our students use the apparatus for a meltiw point depression experiment. -i Each student freezes a solution in a separate 25 x 150 mm test tube, requiring the apparatus only for the 6 mi". needed to obtain data far a melting curve. Thus, one apparatus serves eight students in a lab&ory period. Results obtained from their determinations of molecular weights of organic acids were significantly more accurate than those obtained with the previous apparatus. With minor p r d u r a l changes, this apparatus can be used for a freezing point depression experiment. Our apparatus used in conjunction with the stirring arrangement of Marzzaceo and Collins' should makes freezing point depression spparatus that is both accurate and fun to use.
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Marzmrco, C., and Collins, M., J. CHEM. K D L ' C . , ~650 ~ , (19HO). 2 A u t h ~to ~ rwhom correspondence should be sent. Additiunal details ahout the apparatus will be furnished upon request. Charles Slngman Judy Sophlanopoulos2 Ronald Johnson Emory University A ~ I s ~ +GA =
682
Journal of Chemical Education
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