Citric acid, ionization constants

TABLE 10.1. Citric Acid Ionization Constants from Selected Literature Sources ... 

The three acid ionization constants of citric acid are... 

The ionization of citric acid has been studied in detail by several authors using distinct techniques.30-36 More recently, the protonation of citrate, tartrate and malate have been studied using potentiometric and calorimetric methods to obtain protonation constants and other thermodynamic data for a wide range of ionic strengths and two different temperatures (25 and 37 °C).37 The complexation of Na+ by those ligands37 and of Li+, Na+, K+, Rb+, Cs+ and NH by citrate ions38 has also been investigated. The latter results show how the cation of the ionic medium can influence the ionization equilibria and should be taken into account in corrections for this effect. 

In manufacturing a fruit drink, citric acid is added to water in the amount of 0.1 mol/liter. What is the pH of the resulting solution Use an acid dissociation constant of 8.4 X 10 4 for the ionization of citric acid (assume only the first deprotonation reaction occurs). 

The acid-dissodation constants for common polyprotic acids are listed in V TABLE 16.3, and Appendix D provides a more complete list. The structure of citric acid illustrates the presence of multiple ionizable protons FIGURE 16.12. 

Using values of the ionization product of water K, the dissociations constants of citric acid, Kj, Kj and K3, the corresponding citrate ions sizes and a(Na+)=5.0 A, the distribution of individual species as a function of total concentration of sodium dihydrogen citrate at 25 °C is illustrated in Fig. 3.2. As can be observed, in moderate dilute solutions of sodium dihydrogen citrate, olO" mol dm", the mono-charged H2Cir is dominant anion, HCit is of importance in the 10" mol dm" -10 mol dm concentration range and CiU only for c< 10" mol dm". ... 

Table 3.1 Dissociation constants and thermodynamic functions of the first ionization step of citric acid in water...

Consider citric acid, H3C6H5O7, added to many soft drinks. The equilibrium constants for its step-wise ionization are = 7.5 X 10 , fCa2 = 1.7 X 10 , and = 4.0 X 10 . Write the overall net ionic equation and calculate K for the complete ionization of citric acid. 

Iiich it is an. land hence the ionization constants of such 5 Jl, 3 93, 3 95, fsubstances can be determined without refined n the value 3 97 i temperature control. Thus the first pKg of citric f"34, and so the acid lies between 4 44 and 4 47 throughout the b4 and —O 02), range 12 5 to 91°. Many non-carboxylic organic as 3 93 0 04. iacids are temperature sensitive, for example... 

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