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The Chemical Educator

ISSN: 1430-4171 (electronic version)

Table of Contents

Abstract Volume 15 (2010) pp 277-280

Determination of the Molar Mass of an Unknown Gas with a 2-L Soda Bottle

Carl E. Wagner*, Pamela A. Marshall and Thomas M. Cahill

Arizona State University at the West Campus; Division of Mathematical and Natural Sciences; 4701 W Thunderbird Road; Glendale, AZ 85306,
Received January 14, 2010. Accepted April 9, 2010.

Published: 20 July 2010

Abstract. This laboratory experiment was developed to provide a safe, economical, and effective way to instruct high school or undergraduate general chemistry students in the use of the ideal gas equation to determine the molar mass of an unknown gas using a balance, a modified 2-L soda bottle, and a vacuum source. The experiment was performed by approximately 145 student participants. We assessed the effectiveness of the laboratory by three separate methods: a qualitative pre/post exercise student self-assessment, a quantitative pre/post exercise quiz, and the results of the laboratory experiment. For the qualitative survey, many of the critical concept questions showed a statistically significant (p-value < 0.05 in an unpaired homoscedastic t-test) change from pre- to post-survey, indicating an improved understanding. Similarly, the average on the quantitative pre/post 4-point quiz increased from 1.59 1.21 (sdev) to 2.43 1.21 (sdev), and demonstrated a statistically significant improvement (p-value < 0.001). Finally, 68.1% of the students correctly determined the molar mass of the unknown gas within 2 g/mol, and an additional 6.8% made the determination between 2 g/mol and 4 g/mol. Thus, by all assessment methods we undertook, students were able to perform this experiment and learn from it.

Key Words: Laboratories and Demonstrations; biophysical chemistry; protein; oligomeric; thermal denaturation; circular dichroism spectroscopy

(*) Corresponding author. (E-mail:

Article in PDF format (502 KB) HTML format page number change 7/31/2010

Supporting Materials:

Lab Documentation for Instructor, Lab Handout for Student, Pre- and Post- Quantitative Assessment (Quiz), and Pre- and Post- Assessment (Survey) (36 KB).

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