Autoprotolysis constant of water

In dilute aqueous solutions (the only ones we consider in this chapter), the solvent, water, is very nearly pure, and so its activity may be taken to be 1. The resulting expression is called the autoprotolysis constant of water and is written Kw ... 

The values of pH and pOH are related. To find that relation, we start with the expression for the autoprotolysis constant of water Kw = [H3Oh [Of I ]. Then we take logarithms of both sides ... 

The calculation of pH for very dilute solutions of a weak acid HA is similar to that for strong acids in Section 10.18. It is based on the fact that, apart from water, there are four species in solution—namely, HA, A, H,0 +, and OH. Because there are four unknowns, we need four equations to find their concentrations. Two relations that we can use are the autoprotolysis constant of water and the acidity constant of the acid HA ... 

Kw autoprotolysis constant of water AC/ change in internal energy, e.g. during... 

The pH scale, however, has its limitations. First of all, it is defined for water as the medium. Furthermore, the pH range is limited from 0 (the minimum value of pH in solution) to 14 (the maximum value related to the autoprotolysis constant of water). Moreover, the pH of concentrated solutions deviates significantly from the actual acidity. Below pH values of approximately 1.5, solutions become more acidic than their concentrations would suggest, since the pH beyond this range... 

The autoprotolysis constant of water, K, changes with temperature, pressure and density. The t-p-K and t-p-p-K diagrams of water are shown in... 

Fig. 5. The diagram of the autoprotolysis constant, of water with temperature and pressure, (a) The three-dimensional t-p-log diagram, (b) the four-dimensional t-p-p- og diagram, (c) the variation of log and dielectric constant, with temperature under 25 MPa [11, 12, 42].

These two constants are related by the self-ionization or autoprotolysis constant of water. Consider the ionization of water ... 

The difference between the pH value in water and in a mixture of an organic solvent with water is caused by a change in the autoprotolysis constant of water due to the addition of the organic solvent. 

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