The Chemical Educator
ISSN: 1430-4171 (electronic version)
Abstract Volume 18
(2013) pp 233-237
Metal Ion Identification and Estimation using the Water Absorbent Polymer Polyacrylate
Ling Zhou and Neil D. Danielson*
Department of Chemistry and Biochemistry, Miami University, Oxford, OH, 45056, firstname.lastname@example.org
Published: 13 September 2013
Abstract. Sodium polyacrylate is a synthetic polar (hydrophilic) polymer with carboxyl groups that gives it a very high affinity for water. Typically, the forming gel can swell several hundred times its original size. The polymer does not swell as much in concentrated salt solutions because the cations from the salt will readily interact electrostatically with the carboxylate groups hindering the interaction of the water molecules. We have found that the saturation point of the polymer can be estimated simply by taking a small gel sample, placing it on a funnel with wet filter paper, and noting if droplets of solution pass through. Two experiments have been written. For both experiments, this form of measurement for solutions of different cations such as Li+, Na+ (or K+), and Ca2+ (or Mg2+) at the same concentration can illustrate the dependence of the ion exchange retention mechanism on both cation size and charge. For the analytical (A) chemistry “Experiment A. Metal Ion Estimation using Polyacrylate”, semi-quantification of Na+ and Ca2+ is possible by plotting the volume of solution absorbed versus the molarity of the cation, with different response ranges indicated for each cation. This method can clearly differentiate children Gummie Bear vitamins with calcium and without calcium as well as estimate the sodium content in food seasonings such as soy sauce and seasoning salts. The general (G) chemistry “Experiment G: Metal Ion Identification using Polyacrylate” is simpler, emphasizing polyacrylate identification of either a NaBr, CaCl2, or glucose solid unknown by comparison, when dissolved, to standard solutions of K+, Mg2+, and sucrose. Because both experiments use safe chemicals and minimal equipment, they could easily be adapted for use in middle and high schools as well as college.
Key Words: Laboratories and Demonstrations; general chemistry; analytical chemistry; ion exchange; quantitative analysis; metals
(*) Corresponding author. (E-mail: email@example.com)
Three supporting files are available. Experiment A and Experiment G, laboratory handouts for students and Instructors' notes (1.03 MB).