E. C. Shearer and M. 1. Rumpel Fort Hays Kansas State College Hays, Kansas 67601
I I
Physical Properties of Primary AICO~OIS An experience in physical chemistry
Understanding what physical properties are, methods by which they can he measured, and how they can be applied to other experimental problems must be one objective of the physical chemistry laboratory program. Several methods have been devised to accomplish this goal. These include experiments on one specific property and its measurement, such as viscosity (I), and instructing the student in the measurement of a physical property while using it as an experimental tool in a different experiment, such as following reaction rates by conductivity (2). Neither approach teaches physical properties satisfactorily. Other improved methods of teaching physical properties have been desimed. Slowinski ( 3 ) has instructed students to measure ten properties of an unknown liquid by 12 methods in ten weeks time. Coolidge ( 4 ) has required measuring properties on an unknown liquid, on benzene, and on solutions of the two. These methods consume a lot of time.. . oerhaos at the exoense of other useful and necessary laboratory problems. We wish to present a more flexible aooroach which rewires a much smaller time pe.. riod. The Experiment The experiment is a class project to measure, interpret, and correlate a set of physical properties of a homologous series of compounds over a temperature range. Initially a series of homologous liquids, such as primary alcohols, is selected. One member of the series is assigned to each pair of students. A temperature range and a set of physical properties are chosen for study. Properties and methods of measurement are usually chosen which students will not encounter elsewhere in their undergraduate background. When the experimental work is -completed, the data is cornoiled and distributed to each student. Each student submits a laboratory report in which he rigorously describes the physical properties examined, how they can he measured, and his correlations and interpretations. Some students choose to introduce other properties, such as boiling point, from literature values for further correlation purposes. Results and Discussion The results can be demonstrated adeauatelv from data and corkations submitted exclusively by students in the s ~ r i n e .1972. semester. These students examined density dy w&tpha1 balance, viscosity by Ostwald viscometers, surface tension by a tensiometer and the capillary rise method, conductivity, and refractive index by the Abbe refractometer. Each property was measured a t 25, 35, and 45"C, for the first five primary alcohols. Figure 1, a plot of refractive index versus temperature, is one example of how students presented the data. Literature values are plotted on the graph for comparison to accepted standards (5, 6). They observed linear rates of change ranging from 3.7-4.5 x units per degree. The 0.06% error of the ethanol line at 20°C is experimentally acceptable ( 4 ) . Presented at the 1st Rocky Mountain Repional Meeting of the American Chemical Society, June30, 1972. 140
/
Journal of Chemical Education
Figure 1. Temperature-refractive index relationship of the first five primary alcohois.
89"
PRIMARY ALCOHOLS
2 .O 3.0 VISCOSITY. CP.
1.0
4.0
Figure 2. The relationship of carbon chain length to viscosity tor the first five primary alcohols.
A second method of data presentation is exemplified by Figure 2. When carbon chain length is plotted against viscosity, the points for each temperature form a zig-zag pattern about the best straieht line., a . oattem observed from plotting more extensive literature values. Within experimental error. each line extra~olatedthroueh a common point. These examples offer only a small sample of the correlations done by the students. The limit to the number of things that can be done is the allotted time.
-
Conclusion This approach has been well received by the physical chemistry students. There has been an appreciation established for physical properties and their measurement. They have seen the need for goad technique and the need to strive for an added significant figure in accuracy. They have discovered that literature values for these properties are not as easily found as anticipated. and that predictable relationships exist in systems bf this kind. The approach is flexible in that numerous options are available. Different series of compounds may he selected. Many variations can he made in properties and measuring techniques. A study comparing different methods of measuring a particular property can be devised. An analysis of student performance can he made by having all students perform the same tasks.
Lilerature Cited 11) Daniele. F-em.
Williams, J. W.,Bender. Paul, Alberty, R. A.. Cornwell, C. D., and H-men, John E., "Exptimentd Physical Chcmistm" 7th Ed., McOrawHillBmk Co.. NcaYork. 1970, p. 157. (2) Daniels. Farrin@on. Williams, J. W.. Bender. Paul, Albrty, R. A.. C m a e l l , C. D., and Hamiman. John E., "Fzprimmtai Phylieal Chembtry: 7th Ed., MeGraa-
H~~IE (31 51-8 I11 Cmlidgl, EdwinC .,.. ... I51 Weast. Robert C., (Editor-in-Chkfl, "Handbook af Chrmktry and Pbysifs;. ~ l U l Ed., The Cbcmieal Rvbber Co., Cleveland, Ohio. 1 W . @) Lange, N. A., (Editor), "Handbmk of Chemiatry;'&h Ed.. Handbmk Publhhem, Inc..Sanduaky, Ohio,1952.p.1307.
Volume51, Number 2, February 1974
/
141
