Ka, acidity constant

Ka acidity constant ( acid dissociation s stoichiometric ratio... 

Ka acidity constant for the dissociation of weak acid radiation dose)... 

Ka = Acidity constant cm = Centimeter en = Ethylendi-amine LD50 = 50% of a lethal dose Et = ethyl i-Bn = Isobutyl hep = Hexagonal close packed i-Pr = Isopropyl LED = Light-emitting diode Me = Methyl MOCVD = Metalorganic chemical vapor deposition E° = Normal standard potential NMR = Nuclear magnetic resonance n-Bu = n-butyl n-Pr = n-propyl OEP = Octaethylporphyrin i-Bu = Tert-butyl THE = Tetrahydrofurane TPP = Tetraphenylporphyrin V = Volt. 

In the dilute aqueous solution normally used for measuring acidity, the concentration of water, H20], remains nearly constant at approximately 55.4 M at 25 °C. We can therefore rewrite the equilibrium expression using a new quantity called the acidity constant, Ka. The acidity constant for any acid HA is simply the equilibrium constant for the acid dissociation multiplied by the molar concentration of pure water. 

Recall from the earlier discussion of acidity in Sections 2.7 through 2.11 that the strength of any acid HA in water can be expressed by an acidity constant, Ka. 

Like other Bronsted-Lowry acids discussed in Section 2.7, carboxylic acids dissociate slightly in dilute aqueous solution to give H30+ and the corresponding carboxylate anions, RC02. The extent of dissociation is given by an acidity constant, Ka. 

Acidity constant, Ka (Section 2.8) A measure of acid strength. For anv acid HA, the acidity constant is given bv... 

Quantitative studies based on kinetic measurements using strongly electrophilic diazonium ions and, as coupling components, 1-naphthol, 2-naphthol-6-sulfonic acid, and resorcinol in aqueous acid were made by Sterba and coworkers (Kropacova et al., 1970 Kavalek et al., 1970 Sterba and Valter, 1972 Machackova et al., 1972a). In a typical case (2,6-dichloro-4-nitrobenzenediazonium ion and 1-naphthol) the dependence of the logarithm of the measured rate constant (ks) on pH was linear with a slope of 1. At pH < 1, however, a practically constant value of ks was obtained. The measured rate constants therefore correspond to Scheme 12-62, in which the first term relates to the reaction of the naphthoxide ion and the second to that of the undissociated naphthol Ka is the acidity constant of 1-naphthol. 

Because the solutions that we are considering are dilute and the water is almost pure, the activity of 1120 can be set equal to l. The resulting expression is called an acidity constant, Ka. If we make the further approximation of replacing the activities of the solute species by the numerical values of their molar concentrations, we can write the acidity constant expression for acetic acid as... 

In this expression, Ka is the acidity constant of a weak acid and Kh is the basicity constant of the conjugate base of that acid. The acid and base must form a conjugate acid-base pair (such as CH C00H/CH3C02 or NH4+/NH3). We can express Eq. 1 la in another way by taking logarithms of both sides of the equation ... 

For each of the following weak bases, write the proton transfer equilibrium equation and the expression for the equilibrium constant Kh. Identify the conjugate acid, write the appropriate proton transfer equation, and write the expression for the acidity constant Ka. (a) (CH3)2NH, dimethylamine ... 

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

It is important to remember that the value of the acidity constant, Ka, of an acid is related to the standard free energy change for the ionisation, AG°, by the relation... 

Equilibria involving acids and bases are discussed from within the Lowry-Br0nsted theory, which defines an acid as a proton donor and a base as a proton acceptor (or abstracter ). The additional concept of pH is then introduced. Strong and weak acids are discussed in terms of the acidity constant Ka, and then conjugate acids and bases are identified. 

The resultant (modified) equilibrium constant is called the acidity constant of phenol, and has the new symbol Ka, which has a value is 10-10 for phenol. Ka is also called the acid constant, the acid dissociation constant or just the dissociation constant. The value of Ka for phenol is clearly tiny, and quantifies just how small the extent is to which it dissociates to form a solvated proton. 

Having categorized acids into strong and weak via the concept of acidity constants Ka, we now look at the strengths of various... 

Consider a weak acid, HA, dissociating HA —> H30+ -I- A-. Its acidity constant Ka is given by... 

The intrinsic acidity constants Ka and Ka2 can then be determined from Q, and Qa2 as follows. Combination of Equations 19 and 20 with Equations 1 and 2 show that the acidity constants are related to the acidity quotients by... 

Figure 6. Use of Method I, Equation 22, to calculate surface acidity constants with Ng - 12 sites nm" log Ka = -3.5 and log Ka2 = -8.1 or, in other terms, pHZpC = 5.8 and log Kd - -2.3. Capacitances were determined from the slopes according to Equation 22 acid branch, 0.77 F m base branch, 0.89 F m. Data are from Figure 5, Ti02 in 0.1 M KNO3 (32). ...

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