Product ionic of water

Because the ionic product of water = [H ] [OH ] = 1.04 x 10" at 25°C, it follows that pH = 14 - pOH. Thus, a neutral solution (e.g., pure water at 25°C) in which [H j = [OH ] has a pH = pOH = 7. Acids show a lower pH and bases a higher pH than this neutral value of 7. The hydrogen ion concentrations can cover a wide range, from -1 g-ion/liter or more in acidic solutions to -lO" " g-ion/liter or less in alkaline solutions [53, p. 545]. Buffer action refers to the property of a solution in resisting change of pH upon addition of an acid or a base. Buffer solutions usually consist of a mixture of a weak acid and its salt (conjugate base) or of a weak base and its salt (conjugate acid). 

The typical strong acid of the water system is the hydrated proton H30+, and the role of the conjugate base is minor if it is a sufficiently weak base, e.g. Cl-, Br-, and C104. The conjugate bases have strengths that vary inversely as the strengths of the respective acids. It can easily be shown that the basic ionisation constant of the conjugate base KR canj is equal to Kw/KA conj, where Kw is the ionic product of water. 

Table 2.1 Ionic product of water at various temperatures...

The hydrolysis constant is thus related to the ionic product of water and the ionisation constant of the acid. Since Ka varies slightly and Kw varies considerably with temperature, Kh and consequently the degree of hydrolysis will be largely influenced by changes of temperature. 

Kw ionic product of water Ka = dissolution constant of weak acid ... 

As the pure solvent is only slightly ionized, both the activity coefficients and the concentration of the non-ionized solvent molecule may be regarded as unity, and one prefers to use Kw = [H30+][0H ], the so-called ionic product of water. It was determined for the first time by Kohlrausch and Heydweiller at 18° C from the conductivity, k = 0.0384 10"6 (cf., Ch. 2), which is given by... 

Yakolev, Y. B. Kul ba,F. Y. Zenchenko, D. A., Potentiometric measurement of the ionic products of water in water-dimetylsulphoxide, water-acetonitrile and water-dioxane mixtures, Russ. J. Inorg. Chem. 20, 975-976 (1975). 

Thus [H-i]=[OH ] and fioo-i=Kw, the ionic product of water. Refer also to the last column in the Model matrix. 

This equilibrium constant or dissociation constant for the ionisation of water is known as the ionic product of water and is given the symbol K. As is an equilibrium constant, its value is dependent on temperature. At 24°C the value of is approximately 1 x 10 T... 

Ddx distribution constant for x (specified) for example, v = R, or = HA, for undissociated extractant (reagent), = C for neutral (e.g., metal-containing) complex Dsp solubility product Kyj ionic product of water... 

C) which he derived from the ionic product of water (Kw = 10 14 mol x dm 3). Some years later, Lewis introduced the concept of activity, and in 1923 Debye and Hiickel published their theory for strong electrolyte solutions. On the basis of this knowledge, Soerensen and Linderstroem-Lang [2] suggested a new pH definition in terms of the relative activity of hydrogen ions in solution ... 

Fig. 4. knjkh for spontaneous reactions. (Open circles are experimental points for nitramide, filled circles experimental points for acetic anhydride. The respective curves are calculated from equation (165) with jS=0-75 and from equation (166) with a=0-5. The bottom curve reproduces equation (131) for the ionic product of water.)... 

The other application explained here is the ionic product of water, pKw [11], which is essentially the equilibrium constant of the auto-ionization process of water (Kw =... 

The constant KV) which is called the ionic product of water, may be computed from equations (V-44) and (V-46), if partial molal free energies (potentials) of formation of all the reaction components in the corresponding standard states are known. For such standard states we select both the state of a hypothetical ideal solution with molal concentration of hydrogen and hydroxyl ions equalling unity and the state of hypothetical, absolutely undissociatcd pure water. Since in actual diluted solutions the activity of undissociated water hardly differs from the activity in its standard state, aji2 in the equation (V-51) may be considered as equalling unity so that then Km = K . The following expression is valid for a temperature of 25° C ... 

From accurate electrochemical measurements the ionic product, of water will result Kv = 1. 008 x 10-u. 

If we take into account the ionic product of water h+- oh 10-14 this equation can be transformed in the following manner ... 

Since, for dilute solutions, the activity a (Chap. 10) of water is considered to be constant and very close to 1.0, and the activities of the solutes may be represented by their concentrations, we can define a practical constant, Kw, called the ionic product of water ... 

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