Flame Emission Spectrometry in the General Chemistry Laboratory: (I) Determination of Sodium Concentration and (II) Preparation and Assessment of Student-Prepared Sodium Solutions

TCE

The Chemical Educator

ISSN: 1430-4171 (electronic version)

Table of Contents

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, Box 351700, Seattle, WA 98195, nyasulu@chem.washington.edu
Received April 12, 2005. Accepted August 7, 2005.

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: nyasulu@chem.washington.edu)

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Supporting Materials:

Two supporting files, a laboratory handout and data sheet for students are available in a Zip file (257 KB).