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African Journal of Chemical Education

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Donor-acceptor reactions: Good bye to the laboratory jargon

Hans-Dieter Barke, Nina Harsch

Abstract


For chemistry education we are discussing mainly two concepts of acids and bases: theories of Arrhenius and Broensted. The first theory discusses the dissociation of molecules into ions: hydrochloric acid solution contains H+ (aq) ions and Cl-(aq) ions, sodium hydroxide solution contains Na+(aq) ions and OH-(aq) ions. This theory therefore deals with substances, which are acids or bases – it would be even better to take the logical names "acidic and alkaline solutions". If both solutions are mixed in equivalent quantities, the H+ (aq) ions react with OH-(aq) ions to form H2O molecules, while the other ions remain in solution. The Broensted theory defines protolysis and proton transfers: a molecule or an ion transfers a proton (H+ ion) to another molecule or ion; two conjugated acid-base pairs are involved. Thus, Broensted acids and bases are no more substances, but individual types of particles. Due to the autoprotolysis of H2O molecules (not "autoionization of water"), the following equilibrium exists: H2O + H2O H3O+(aq) + OH-(aq) Through this protolysis it is more advantageous to argue rather with H3O+(aq) ions than with H+(aq) ions. In this theory there are still ampholyte particles which react as acid or as base particles – depending on the reaction partner: H2O molecules, NH3 molecules, HSO4- ions. Water, ammonia or sodium hydrogen sulfate cannot be regarded as ampholytes – pure water cannot be one time an acid and another time a base: with the pH of 7 it is always a neutral substance. The article will show  misconceptions of students and point out the better terminology: reflecting this terminology, students should develop a better understanding of Chemistry! [African Journal of Chemical Education—AJCE 6(1), January 2016]



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