Triprotic acids phosphoric acid

FIGURE 11.13 The variation of the pH of the analyte solution during the titration of a triprotic acid (phosphoric acid). The major species present in solution at the first two stoichiometric points (B and D) and at points when half the titrant required to reach a stoichiometric point has been added (A, C, and Ej are shown. Compare this diagram with Fig. 10.21. The labels SP1, SP2, and SP3 denote the volumes of base required to reach the three stoichiometric points. Points A through F are explained in the text. 

Acids that contain three hydrogen ions are called triprotic acids. Phosphoric acid, H3P04(aq), is a triprotic acid. It gives rise to three anions, as follows ... 

In picturing reactions of a polyprotic acid with a strong base, we shall assume that enough base is added to react with all of the acidic hydrogen atoms. The following complete equations describe the reactions of the diprotic acid sulfuric acid and the triprotic acid phosphoric acid with sodium hydroxide. Each equation represents the sum of a series of reactions in which the acidic hydrogen atoms are removed one at a time. 

Phosphoric acid (H3PO4) is a triprotic acid, phosphorous acid (H3PO3) is a diprotic acid, and hypophosphorous acid (H3PO2) is a monoprotic acid. Explain this phenomenon. 

Phosphoric acid, a common ingredient of cola drinks, is triprotic ... 

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 ... 

Neutralisation reactions. The equivalent of an acid is that mass of it which contains 1.008 (more accurately 1.0078) g of replaceable hydrogen. The equivalent of a monoprotic acid, such as hydrochloric, hydrobromic, hydriodic, nitric, perchloric, or acetic acid, is identical with the mole. A normal solution of a monoprotic acid will therefore contain 1 mole per L of solution. The equivalent of a diprotic acid (e.g. sulphuric or oxalic acid), or of a triprotic acid (e.g. phosphoric( V) acid) is likewise one-half or one-third respectively, of the mole. 

Phosphoric acid, H P04, is a triprotic acid. Write the equation for complete reaction with KOH.)... 

For each of the following polyprotic acids, state which species (H2A, HA, or A2 of the diprotic acid or H3A, H,A, HA2, or A for triprotic acids) you expect to be the form present in highest concentration in aqueous solution at pH = 5.0 (a) tartaric acid (b) hydrosulfuric acid (c) phosphoric acid. 

Phosphate, PO, is the fully dissociated anion of triprotic phosphoric acid, H3PO4 ... 

An acid that contains more than one acidic hydrogen atom is caiied a polyprotic acid. Figure 17-8 shows the structures of two poiyprotic oxoacids, suifuric acid (H2 SO4, diprotic) and phosphoric acid (H3 PO4, triprotic). Many carboxyiic acids are poiyprotic, too. Tabie 17-2 lists several examples of polyprotic acids. 

Consider phosphoric acid, H3P04 (a triprotic acid), and phosphorous acid, H3P03 (a diprotic acid). Two structures that show this acidic behavior are ... 

Each H atoms attached to an O atom is an acidic hydrogen and can be released by the acid to a base. Phosphoric acid has 3 such H atoms and thus is triprotic. Although phosphorous acid has 3 H atoms, only 2 H atoms are bonded to an O atom, the other one is attached directly to the P atom. Thus phosphorous acid is only diprotic. A way to write this is H2PH03. 

If the acid contains more than one ionizable hydrogen, the acid is known as a polyprotic acid. Specifically, diprotic acids, such as sulfuric acid, H2S04, contain two ionizable hydrogens and triprotics, such as phosphoric acid, H3P04, contain three ionizable hydrogens. 

Q dD Phosphoric acid, H3P04(aq) is triprotic. It has three hydrogen ions that may he dissociated. 

Phosphoric acid behaves as a triprotic acid, having three ionizable hydrogen atoms. The hydrogen ions are lost sequentially. The chart below provides the ionization constants and their logs. 

Although its formula suggests that it should be a triprotic acid, H3P03 is in fact diprotic because one of the H atoms is attached directly to the P 4 Phosphorous acid, H3P03 atom and the P—H bond is nonpolar (Section 10.9). 

Phosphorous acid (H3P03) is a weak diprotic acid because only two of its three H atoms are bonded to oxygen. The H atom bonded directly to phosphorus is not acidic because phosphorus and hydrogen have the same electronegativity and the P-H bond is nonpolar. In phosphoric acid, however, all three hydrogens are attached to oxygen, and thus phosphoric acid is a weak triprotic acid. The geometry about the P atom in both molecules is tetrahedral, as expected. Note that the successive dissociation constants decrease by a factor of about 105 (Section 15.11). 

A triprotic acid has three hydrogen ions to donate. For example, phosphoric acid (H3P04) is a triprotic acid. 

Preparation of a Phosphate Buffer What molar ratio of HPC>1 to H2P04 in solution would produce a pH of 7.0 Phosphoric acid (H3P04), a triprotic acid, has 3 pKa values 2.14, 6.86, and 12.4. Hint Only one of the pKa values is relevant here. 

Normality (N) is the number of equivalents of the solute per liter of solution. A1.0 N solution of acid (or base) contains one equivalent of an acid (or base) per liter of solution. A 1.0 M solution of HCl is 1.0 N, but a 1.0 M solution of H2SO4 is 2.0 N. Sulfriric acid has two acidic hydrogens, and the molarity is multiplied by a factor of 2. Phosphoric acid (H3PO4) is triprotic (having three protons it can donate) and a 1.0 molar solution is 3.0 normal. 

Phosphoric acid is a triprotic acid (three protons) that dissociates in the following steps ... 

The common amino acids are simply weak polyprotic acids. Calculations of pH, buffer preparation, and capacity, and so on, are done exacdy as shown in the preceding sections. Neutral amino acids (e.g., glycine, alanine, threonine) are treated as diprotic acids (Table l-l). Acidic amino acids (e.g., aspanic. acid, glutamic acid) and basic amino acids (e.g., lysine, histidine, arginine) are treated as triprotic acids, exactly as shown earlier for phosphoric acid. 

All the acids in Table 10.9 are diprotic, except for phosphoric acid, which is triprotic. 

P4O10 is the anhydride of phosphoric acid, H3PO4. It traps and reacts with water very efficiently and is widely used as a drying agent. Phosphoric acid is a triprotic acid. It is only mildly oxidizing, despite the fact that phosphorus is in a high oxidation state. Phosphoric acid is the parent acid of phosphate salts that contain the tetrahedral phosphate ion, P04 ". Phosphates are generally not very soluble, which makes them suitable structural material for bones and teeth. 

If a buffer is required to control the pH of a neutral solution, use is made of the second ionisation of phosphoric acid. Phosphoric acid is a triprotic acid, which requires three equivalents of NaOH as follows ... 

Curve A in Figure 15-4 is the theoretical titration curve for triprotic phosphoric acid. Here, the ratio approximately 10, as is This ratio results in... 

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