Water ionic product constant

Tabie 16.1 The ionic product constant of water at various temperatures... 

The ionic product constant of water (K ) may be used to calculate the hydroxide ion concentration in solutions of acids. It may also be used to calculate the hydronium ion concentration in solutions of bases. 

Table 2.4 Thermodynamic constant of water ionic product (-temperature range 0-800 C and pressme range 0.1-500 MPa Shvarov, 1992).

A wide variety of acid—base equilibria problems can be solved using the relationships between pH, hydrogen ion concentration and hydroxide ion concentration in conjunction with the ionic product constant of water. 

The relationship between temperature and the ionic product constant of water... 

At 60°C, the ionic product constant of water is 9.55 x 10" moFdm . Calculate the pH of a neutral solution at this temperature. 

The laboratory temperature during titration is rarely equal to the ambient temperature or process temperature. The sample pH will change with temperature since the dissociation constants and water ionic product change with temperature. This is a change in actual solution pH and is not to be confused with the change in millivolts generated by the glass electrode per the Nemst Equation in Chapter 4. Conventional temperature compensators use a temperature sensor embedded inside the electrode to correct for the Nemst effect. 

This table gives values of pKw on a molal scale, where Kw is the ionic activity product constant of water. Values are from W. L. Marshall and E. U. Franck, 7. Phys. Chem. Ref. Data, 10 295 (1981). 

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. 

The ionic product varies with the temperature, but under ordinary experimental conditions (at about 25 °C) its value may be taken as 1 x 10 14 with concentrations expressed in molL-1. This is sensibly constant in dilute aqueous solutions. If the product of [H + ] and [OH-] in aqueous solution momentarily exceeds this value, the excess ions will immediately combine to form water. Similarly, if the product of the two ionic concentrations is momentarily less than 10-14, more water molecules will dissociate until the equilibrium value is attained. 

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. 

In aqueous solutions, H+ and OH ions are present, owing to the dissociation of water molecules. In dilnte solntions, the activity of water is constant. Hence, for the activities of these ions an eqnation of the type (3.17) is obeyed, too. The ionic product... 

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

The solvent dependence of the reaction rate is also consistent with this mechanistic scheme. Comparison of the rate constants for isomerizations of PCMT in chloroform and in nitrobenzene shows a small (ca. 40%) rate enhancement in the latter solvent. Simple electrostatic theory predicts that nucleophilic substitutions in which neutral reactants are converted to ionic products should be accelerated in polar solvents (23), so that a rate increase in nitrobenzene is to be expected. In fact, this effect is often very small (24). For example, Parker and co-workers (25) report that the S 2 reaction of methyl bromide and dimethyl sulfide is accelerated by only 50% on changing the solvent from 88% (w/w) methanol-water to N,N-dimethylacetamide (DMAc) at low ionic strength this is a far greater change in solvent properties than that investigated in the present work. Thus a small, positive dependence of reaction rate on solvent polarity is implicit in the sulfonium ion mechanism. 

Water dissociates to form ions according to Equation (6.2). The ionic product of the concentrations is the autoprotolysis constant Kw, according to Equation (6.4). Taking logarithms of Equation (6.4) yields ... 

Under these conditions, the formation rate constant, k, can be estimated from the product of the outer sphere stability constant, Kos, and the water loss rate constant, h2o, (equation (28) Table 2). The outer sphere stability constant can be estimated from the free energy of electrostatic interaction between M(H20)q+ and L and the ionic strength of the medium [5,164,172,173]. Consequently, Kos does not depend on the chemical nature of the ligand. A similar mechanism will also apply to a coordination complex with polydentate ligands, if the rate-limiting step is the formation of the first metal-ligand bond [5]. Values for the dissociation rate constants, k, are usually estimated from the thermodynamic equilibrium constant, using calculated values of kf ... 

In this section, you determined the solubility product constant, Kgp, based on solubility data. You obtained your own solubility data and used these data to calculate a value for Kgp. You determined the molar solubility of ionic solutions in pure water and in solutions of common ions, based on their Ksp values. In section 9.3, you will further explore the implications of Le Chatelier s principle. You will use a reaction quotient, Qsp, to predict whether a precipitate forms. As well, you will learn how selective precipitation can be used to identify ions in solution. 

Recently, the supercritical fluid treatment has been considered to be an attractive alternative in science and technology as a chemical reaction field. The molecules in the supercritical fluid have high kinetic energy like the gas and high density like the Uquid. Therefore, it is expected that the chemical reactivity can be high. In addition, the ionic product and dielectric constant of supercritical water are important parameters for chemical reaction. Therefore, the supercritical water can be realized from the ionic reaction field to the radical reaction field. For example, the ionic product of the supercritical water can be increased by increasing pressure, and the hydrolysis reaction field is realized. Therefore, the supercritical water is expected as a solvent for converting biomass into valuable substances (Hao et al., 2003). 

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... 

In pure water, the concentrations of and OH must be equal because the dissociation of HjO yields the same number of each of them. You can calculate the ionic concentrations from the equilibrium equation and the ion-product constant ... 

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