Acid-base properties of water

With respect to the well-known acid/base properties of water, ammonia, and phenol in aqueous solution, one has to conclude that enormous solvation energies must contribute to the differences from the behavior of isolated water molecules. 

So, the pH of pure water is 7.00 because that is the negative logarithm of the hydrogen ion concentration that is generated by the self ionization of water. It is a value based on the inherent acid-base properties of water. 

In contrast to the acid/base behaviour of polymeric bulk water, monomeric water is a relatively weak acid and base in the gas phase compared to its substituted derivatives (R—OH, R—O—R, etc.), whose conjugated base or acid ions are stabilized by polarization of the alkyl groups. The gas-phase basicity of water is 138 kJ/mol (33 kcal/mol) below that of ammonia. Its gas-phase acidity is comparable to that of propene and it is less acidic than phenol by about 167 kJ/mol (40 kcal/mol). With respect to the well-known acid/base properties of water, ammonia, and phenol in aqueous solution, one has to conclude that enormous solvation energies must contribute to the difference from the behaviour of isolated water molecules. See Section 4.2.2 for further discussions and references. 

I See the Saunders Interactive General Chemistry CD-ROM, Screen 1 7.3, Acid-Base Properties of Water. 

This reaction is sometimes called the autoionization of water. To describe the acid-base properties of water in the Brpnsted framework, we express its autoionization as follows (also shown in Figure 15.1) ... 

THE ACID-BASE PROPERTIES OF WATER Review Questions... 

The acid—base properties of water, together with its solvent polarity, mean that free charged groups (ions) are common, and most biological macromolecules must be regarded as polyelectrolyes large molecules with multiple charges. 

The acid-base properties of water play an important part in biological processes because of the central role of water as a solvent. The extent of self-dissociation of water to hydrogen ion and hydroxide ion. 

The value pH = 7 plays an important role in characterization of acid-based properties of water. Water with pH < 7 has excess of protons and properties of acid, and water with pH > 7 experiences deficit of protons and has properties of alkali. Neutral pH value depends on temperature and pressure, therefore, it changes with depth. With the increase in temperature it noticeably declines, from 7.47 at 0 °C to 6.13 at 100 °C and to 5.64 at 200 °C (Table 2.4 and Figure 2.3). For fresh waters this correlation may be expressed in equation (Dickson and Riley, 1979)... 

Next, we examine the acid-base properties of water and define the ion-product constant for the autoionization of water to give H and OH ions. (15.2)... 

Acid-Base Properties of Water and the pH Scale Water acts both as a Br0nsted acid and as a Br0nsted base. At 25°C, the concentrations of and OH ions are both at 10 M The pH scale is estabhshed to express the acidity of a solution—the smaller the pH, the higher the concentration and the greater the acidity. 

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