“Dyeing” Sodium Polyacrylate with Metal Ions—Student Laboratory Kit

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Sodium polyacrylate, the superabsorbent polymer found in disposable diapers, absorbs immense amounts of water. Did you know that it will also remove heavy metal cations from solution? The cross-linked polymer contains a large number of sodium ions. When it is placed in a solution containing other metal ions, they preferentially bind to the anionic sites in the polymer, displacing the sodium ions and resulting in the formation of new, colored metal polymers. Students will first observe the ion-exchange properties of sodium polyacrylate by testing the ability of the polymers to decolorize solutions of copper and iron ions. Then, students will determine the exchange capacity of the polymer by measuring the amount of copper removed from a standard solution of copper(II) ions using colorimetric analysis. Complete for 30 students working in pairs. Requires a spectrophotometer or colorimeter.