JCE classroom activity connections: NaCl or CaCl_2, smart polymer gel tells more

摘要

This activity successfully demonstrates how differently CaCl_2 and NaCl affect the behaviors of the superabsorbent polymer gel. It can be adapted as a follow up experiment to the featured classroom activity. This extension explores the effect related to the charges on metal ions, monovalent versus polyvalent, on the gel stability. The chemistry involved in the gel contraction and swelling and the applications of the polymer gel in water softening and deionizing are revealed. The students can also experience an example of Le Chatelier's effect through the performance of the reverse ion exchange of the contracted gel. Other compound pairs of monovalent versus polyvalent metal ions involving LiCl, NaCl, KCl, CaCl_2, BaCl _2, ZnCl_2, CuSO_4, Fe(NO_3) _3, and Al(NO_3)_3 give similar results in the activity of reswelling versus non-reswelling. Students could be encouraged to examine all these compounds, look for similarities in the results, and organize the compounds into groups of monovalent or polyvalent metal ions. Moreover, the formation of colored gels from polymers contracted with Cu~(2+) and Fe~(3+) ions provides evidence that the polymer gel is capable of adsorbing polyvalent metal ions.