Temperature Measurement: A General Chemistry Experiment The type of experiment that is suitable for chemistry students a t the beginning of the introductory general course is restricted by the students' limited laboratory experience and knowledge of the subject. Temperature is a concept introduced early in most texts which all students have some experience with and intuitive feeling for. We have found, though, that the beginning chemistry student does not have a knowledge of the origin of temperature scales and their relationship to one another. The following experiment, which can be readily performed in one hour, was designed to alleviate this weakness. Each student is given an uncalibrated mercury thermometer.' Using a 30-cm ruler and grease marking pencil, a scale is arbitrarily marked off on the thermometer with the only restriction being that the scale he Linear. The ruler can be used later as an aid in estimating readings which fall between markings. The mark nearest to the thermometer bulb is ar5itrarily assigned as OoS ('S = student temperature scale) and the remaining divisions are numbered. This scale should be constructed before any temperature measurements are made to eliminate the problem of students constructing a scale identical to a common temperature scale. The freezing point and boiling point of the reference, water, are determined to the nearest 0.1 division on their scales by using standard procedures. Each student then determines the boiling point of an unknown on his temperature scale. The student then converts this temoerature to demees Celsius bv derivine the relationshio between his temperature scale and the Celsius scale based on thr dntn collected. To allow the student to readily arrive at the equation relating any two h e a r temperacure scales. X and Y, the following generalized equation is presented m the introduction to the rxperiment ~~~~~
~~~~~
"X P
-
FP,,., -
P
=
"Y - FP, ref BP,,.t - FP,,.,
FP, ..r and BP, ,,r are the freezing and boiling points of the reference substance on the X temperature scale and FP,
..r
and BP, ,r are the freezing and boiling points of the same reference substance an the Y temperature scale. This equation allows the development of a conversion equation between any two linear temperature scales and is also illustrative of the origin of the two temperature scales. The results obtained on the unknown are good. In a group of typical students better than 80% of the students determined the boiling point of an unknown to within *2'C. Acopy of the experimental write-up distributed to students will be provided to interested persons. 'Brooklyn Thermometer Co., Inc., 90Verdi St., Fsrmingdsle, N.Y. 11735. University of Wismnsin-Parkside Kenosha, 53140
660
/
Journalof Chemical Education
Douglas N. Thompson LaVerne C. Quass
