The Chemical Educator
ISSN: 1430-4171 (electronic version)
Abstract Volume 10
Issue 6 (2005) pp 437-439
Flame Emission Spectrometry in the General Chemistry Laboratory: (I) Determination of Sodium Concentration and (II) Preparation and Assessment of Student-Prepared Sodium Solutions
Frazier W. Nyasulu,* William Cusworth III, and John Macklin
Department of Chemistry, University of Washington,
351700, Seattle, WA 98195, firstname.lastname@example.org
Published online: 3 November 2005
Abstract. In this general chemistry laboratory, the concentration of sodium in Coca-Cola, Gatorade, and seawater is determined by flame emission spectrometry. This laboratory also addresses the serious problem that we and many others have noticed: students do not know how to prepare solutions accurately, especially dilute solutions. Students are required to prepare the following sodium solutions: 1.00 ´ 10–4 M Na+ from NaCl, 2.5 mg Na+/8 fl. oz. from Na2SO4, 5.5 mg Na2SO4/8 fl. oz., and 15 ppm Na+ (from Na2SO4) in a buffer solution of pH 4.0. The accuracy of these solution preparations is graded using reference solutions, a flame photometer, and a pH meter. In order to encourage careful planning and to conserve materials, we only provide 1.5 g of NaCl and 2.5 g of Na2SO4. Students working in groups of four earn full points if they succeed on the first attempt and earn only 50% of the points if they succeed on the second attempt. The first attempt success rate is lowest for the 15 ppm solution (25%) and highest for the 1.00 ´ 10–4 M Na solution (45%). The combined first and second success rate is in the range 65% to 85%. Following this exercise, students have a much better understanding of how to prepare solutions.
Key Words: Laboratories and Demonstrations; general chemistry; atomic spectroscopy; quantitative analysis; stoichiometry; solutions
(*) Corresponding author. (E-mail: email@example.com)
Two supporting files, a laboratory handout and data sheet for students are available in a Zip file (257 KB).
Issue date: December 1, 2005