Diprotic adds

To treat acid-base equilibria involving zwitterions, it is convenient to consider the cation stable at low pH to be a diprotic add (analogous to H2C03), which ionizes in two steps. Using the symbols C+, Z, and A- to stand for the cation, zwitterion, and anion, respectively, we have... 

The common strong acids are sulfuric acid [H2S04(aq )], hydrochloric acid [HCl( 7q )], nitric acid [HNOsl tqr)], and perchloric acid [HC104(<7qf)]. Sulfuric acid is actually a diprotic add, an acid having two acidic protons. The acid H2SO4 is a strong acid, virtually 100% dissociated in water ... 

Carbonie acid is a diprotic add. Write equations for the stepwise ionization of the acid in water. 

Sulfuric acid (H2SO4) is a diprotic add because each unit of the acid gives up two ions, in two separate steps ... 

Although it is a diprotic add = 8.0 X 10 and = 2.5 X 10 ), ascorbic acid only loses one proton under biological conditions to give H and the hydrogen ascorbate ion ... 

A FIGURE 16.9 Titration Curve Diprotic Add with Strong Base This curve represents the titration of 25.0 mL of 0.100 M H2SO3 with 0.100 M NaOH. 

Diprotic adds used for peelings are malic, tartaric and azelaic acids. 

White phosphorus is much more reactive than black or red phosphorus. Explain. How is phosphine s (PHj) structure different from that of ammonia Phosphoric acid (H3PO4) is a triprotic acid, phosphorous acid (H3PO3) is a diprotic add, and hypophosphorous acid (H3PO2) is a monoprotic acid. Explain this phenomenon. 

Carbonic acid is a weak diprotic add (H2CO3) with fCaj = 4.43 X 10- andKa2 = 4.73 X 1Q- . The equivalence points for the titration come at approximately pH 4 and 9. Suitable indicators for use in titrating carbonic acid or carbonate solutions are methyl orange and phenolphthalein. 

Suppose we are titrating the triprotic acid H P04 with a solution of NaOH. The experimentally determined pH curve is shown in Fig. 11.13. Notice that there are three stoichiometric points (B, D, and F) and three buffer regions (A, C, and E). In pH calculations for these systems, we assume that, as we add the hydroxide solution, initially NaOH reacts completely with the acid to form the diprotic conjugate base... 

Takacs-Novak, K., Tam, K. Y. Multiwavelength spectrophotometric determination of add dissodation constants. Part V. Microconstants and tautomeric ratios of diprotic amphoteric drugs./. Pharm. Eiomed. Anal. 2000, 17, 1171-1182. 

Substances containing more than one acidic proton are called po/yprofic adds. Diprotic acids contain two acidic protons, and triprotic acids contain three acidic protons. Acid protons dissociate one at a time and have different Ka andpJC constants. Carbonic acid (H2CO3) is a diprotic acid. 

Plan H2CO3 is a diprotic acid the two add-dissociation constants, K i and (Table 16.3), differ by more than a ctor of 10 Consequently, the pH can be determined by considering only K i, thereby treating the add as if it were a monoprotic add. 

The treatment of diprotic and polyprotic acids is more involved than that of monoprotic acids because these substances may yield more than one hydrogen ion per molecule. These acids ionize in a stepwise manner that is, they lose one proton at a time. An ionization constant expression can be written for each ionization stage. Consequently, two or more equilibrium constant expressions must often be used to calculate the concentrations of species in the add solution. For example, for carbonic acid, H2CO3, we write... 

So now let s turn our attention to the titration of diprotic acids. Figure 11-2 shows calculated curves for 50.0 mL each of three different 0.020 0 M diprotic acids, H2A, titrated with 0.100 M OH . For all three curves, H2A has p/Tj = 4.00. In the lowest curve, p/i2 is 6.00. In the middle curve, p/T2 is 8.00 and, in the upper curve, pA 2 is 10.00. The first equivalence volume (Fei) occurs when the moles of added OH equal the moles of H2A. The second equivalence volume V i) is always exactly twice the first equivalence volume, because we must add the same amount of OH to convert HA to A . Let s consider why pH varies as it does during these titrations. 

The procedure for calculating the pH of a triprotic add is similar to that for a diprotic acid. In this case of a triprotic acid, both the second and third ionizations do not generally affed the pH. For example, phosphoric acid (H3PO4) is a triprotic acid (i.e., it has three ioruzable hydrogen atoms) ... 

What is the difference between (a) a monoprotic acid and a diprotic acid (b) a weak acid and a strong acid (c) an add and a base ... 

The hahdes and oxyhalides of some nonmetak hydrolyze (react with water) to produce two acids a (binary) hydrohalic acid and a (ternary) oxyicid of the nonmetal. Phosphorus trihalides react with water to produce the corresponding hydrohalic acids and phosphorous add, a weak diprotic acid, whereas phosphorus pentahahdes give phosphoric acid and the corresponding hydrohahc acid. The phosphorus fluorides are an exception to this reactivity trend. The P — F bonds are generahy too stable to react with water under mild to moderate conditions. 

Table 14.3 lists the six strong acids. The first five acids in the table are monoprotic adds, acids containing only one ionizable proton. Sulfuric acid is an example of a diprotic acid, an acid that contains two ionizable protons. 

Consider a solution that is 0.10 M in zinc ion and in lead(ll) ion. You add hydrogen sulfide, H2S, to this solution. Hydrogen sulfide ionizes in water as a diprotic acid ... 

Monoprotic and Diprotic Acids Hydrochloric add, HCI, is a strong monoprotic acid. A dilute HCI solution contains hydronium ions and chloride ions. Sulfuric acid, H2SO4, is a strong diprotic acid. A dilute H2SO4 solution contains hydrogen sulfate ions from the first ionization, sulfate ions from the second ionization, and hydronium ions from both ionizations. 

The reaction between NaOH and KHP is a relatively simple add-base neutralization. Suppose, though, that instead of KHP, we wanted to use a diprotic acid such as H2SO4 for the titration. The reaction is represented by... 

Many of the products you use at home contain weak acids. In carbonated soft drinks, CO2 dissolves in water to form carbonic acid, H2CO3, a weak acid. A weak add such as H2CO3 contains mostly H2CO3 molecules and a few H30 and HC03 ions. A weak acid such as carbonic acid, H2CO3, is written with a double arrow. Carbonic acid is a diprotic acid that has two which ionize one at a time. Because HCO3 is also a weak acid, a second ionization produces another hydronium ion and the carbonate ion, C03. ... 

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