Phosphoric acid dissociation constants

Monoprotic weak acids, such as acetic acid, have only a single acidic proton and a single acid dissociation constant. Some acids, such as phosphoric acid, can donate more than one proton and are called polyprotic weak acids. Polyprotic acids are described by a series of acid dissociation steps, each characterized by it own acid dissociation constant. Phosphoric acid, for example, has three acid dissociation reactions and acid dissociation constants. 

Phosphoric acid is a tribasic acid. It is not an oxidizing acid. In aqueous solution phosphoric acid dissociates to H2PO4, HP042 and POs ions. The dissociation constants are as follows ... 

The equilibrium constant, K , is called the acid dissociation constant. Similarly for a polyprotic acid (i.e. phosphoric acid), the equilibrium... 

Dickson A. G. and Riley J. P. (1979b) The estimation of acid dissociation constants in seawater from potentiometric titrations with strong base II. The dissociation of phosphoric acid. Mar. Chem. 7, 101—109. 

Phosphorusiy) Compounds. A new cyclic tetraphosphonic acid with the stoicheiometry C4H12P3O12 can be prepared by heating phosphorous acid and acetyl chloride in a sealed tube at 120 Three acid dissociation constants can be determined and the compound can be obtained as either a tri- or tetra-hydate. N.m.r. and single-crystal Z-ray studies on the hydrated calcium salt show that the compound has structure (25). 27 The anion C4H8P40i is a... 

The terms strong and weak acids are not entirely satisfactory since they are qualitative descriptions. Strong and weak are not absolute terms and some acids, such as phosphoric(v) acid, H3P04(aq), are described as moderately strong. In Chapter 18, a quantitative measure of acid strength that does not vary with dilution, known as the acid dissociation constant, will be introduced. 

Phosphoric acid dissociates to form dihydrogen phosphate and hydronium ion. Phosphoric acid has a of 7.5 X 10 . Write the equation for the reaction and the acid dissociation constant expression for phosphoric acid. 

Find the pH of a solution made from 1.000 kg of water and 0.100 mol of phosphoric acid, H3 PO4, for which the three acid dissociation constants are... 

Phosphorous acid is stronger. It has the smaller p value, which corresponds to a larger acid dissociation constant, K. KJHNO2 =... 

The titration curve of phosphoric acid in the presence of sodium hydroxide is shown in Figure 1. Three steps, corresponding to consecutive replacement of the three acidic hydrogens, and two inflection points, near pH = 4.5 and 9.0, are evident. Dissociation constants are = 7.1 x 10 = 6.3 x 10 ... 

Table 9 includes data on the first dissociation constants of seven weak acids it will be recalled that we expect these to fall into class III. The table includes the second dissociation constants of five acids, phosphoric, sulfuric, oxalic, malonic, and carbonic, which fall into class IV, while the amino acids glycine and alanine provide four examples that should fall into class II. 

A solution containing 0.20 M H3POj, phosphorous acid, is tested with indicators and the H +(aq) concentration is found to be 5.0 X 10 2 M. Calculate the dissociation constant of H3PO3, assuming that a second proton cannot be removed. 

If the dissociation constant of the acid HA is very small, the anion A- will be removed from the solution to form the undissociated acid HA. Consequently more of the salt will pass into solution to replace the anions removed in this way, and this process will continue until equilibrium is established (i.e. until [M + ] x [A-] has become equal to the solubility product of MA) or, if sufficient hydrochloric acid is present, until the sparingly soluble salt has dissolved completely. Similar reasoning may be applied to salts of acids, such as phosphoric(V) acid (K1 = 7.5 x 10-3 mol L-1 K2 = 6.2 x 10-8 mol L-1 K3 = 5 x 10 13 mol L-1), oxalic acid (Kx = 5.9 x 10-2 mol L-K2 = 6.4 x 10-5molL-1), and arsenic)V) acid. Thus the solubility of, say, silver phosphate)V) in dilute nitric acid is due to the removal of the PO ion as... 

A triprotic acid H3A (e.g. phosphoric(V) acid) will similarly yield three dissociation constants, Klt K2, and K3, which may be derived in an analogous manner ... 

Titrations curves for polyprotic acids have an inflection point for each hydrogen in the formula if the dissociation constant (Ka) for each hydrogen is very different from the others and if any dissociation constant is not too small. The titration curves of the polyprotic acids H2S04 and H3P04 are shown in Figures 5.6 and 5.7. Sulfuric acid has essentially one inflection point (like hydrochloric acid—compare with Figure 5.1(a)), while phosphoric acid has two apparent inflection points. Both hydrogens on the... 

Remember Thc strongest acids dissociate most readily. Of the 9 acids listed in Table 10-5, the strongest is sulfuric (1), with the highest acid ionization constant, and the weakest is phosphoric (3). 

Consulting the table of the dissociation constants K s for phosphoric acid shows that the first dissociation is much greater than the second, about 100,000 times greater. This means nearly all the W(aq) in the solution comes from the first step of dissociation. The second and third steps add very little Y (aq) to the solution. So a solution of phosphoric acid will contain H3PO4 molecules in highest concentration with smaller, and nearly equal, concentrations of H and H2PO4. The HPO4 and PO4 ions are present in very small concentrations. 

In milk, the critical dissociation constants are pX, for citric acid, pK for phosphoric acid and pX for carbonic acid. Bearing in mind the limitations and assumptions of the above data, the following calculations can be made for the distribution of the various ions in milk at pH 6.6. 

Equilibrium constants for ionization reactions are usually called ionization or dissociation constants, often designated Ka. The dissociation constants of some acids are given in Figure 2-16. Stronger acids, such as phosphoric and carbonic acids, have larger dissociation constants weaker acids, such as monohydrogen phosphate (Ill Of ), have smaller dissociation constants. 

H3PO4 (phosphoric acid)). The dissociation reactions for each pair are shown where they occur along a pH gradient. The equilibrium or dissociation constant (fCa) and its negative logarithm, the p/Ca, are shown for each reaction. 

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