Ionic reactions, limiting quantities

Net ionic equations are used in discussions of limiting quantities problems (Chapter 10), molarities of ions (Chapter 11), balancing oxidation-reduction equations (Chapter 16), acid-base theory (Chapter 19), and many other areas beyond the scope of this book. They make possible writing equations for halfreactions at the electrodes in electrochemical experiments (Chapter 17), which have electrons included explicitly in them. They make understandable the heat effects of many reactions such as those of strong acids with strong bases. 

In some cases, the net ionic eqnation is significantly simpler than the full equation. For example, consider the reaction of solid calcium carbonate with a limited quantity of hydrochloric acid. (In this case, these substances react in a 1 1 ratio.) Assuming that the chloride ion is a spectator ion allows us to write the net ionic equation direcdy ... 

Barium hydroxide, Ba(OH)2, has limited water solubility. If a small quantity of barium hydroxide is added to a given volume of water, it might dissolve. If a large quantity of barium hydroxide is added to the same volume of water, most of it will not dissolve. Thus, barium hydroxide might appear in an equation as either solid or aqueous. Write a net ionic equation for the reaction of barium hydroxide with HCIO4 for each of these cases. 

Of special interest for the topic of the present chapter is the observation of Weaver that while the double-layer-corrected AS quantities are ligand sensitive, they are found to be independent of potential. This is not the case for the atom and electron transfer process involved in the hydrogen evolution reaction at Hg studied by Conway, et where an appreciable potential dependence of AS is observed, corresponding to conventionally anomalous variation of the Tafel slope with temperature. Unfortunately, in the work with the ionic redox reactions, as studied by Weaver, it is only possible to evaluate the variation of the transfer coefficient or symmetry factor with temperature with a limited variety of redox pairs since Tafel slopes, corresponding to any appreciable logarithmic range of current densities, are not always easily measurable. Alternatively, evaluation of a or /3 from reaction-order determination requires detailed double-layer studies over a range of temperatures. 

They are distinguished by the levelling of both acidic and basic properties in these melts, owing to the solvolysis reactions. The properties of acids are levelled by the formation of an equivalent quantity of acid of the solvent that makes all the strong acids indistinguishable. The properties of strong bases are limited by the basicity of the oxide ion adduct to the most acidic constituent cation of the ionic solvent. Only pK values for weak acids and bases may be determined without appreciable distortions. 

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