Diprotic neutralization

If one were to titrate a weak diprotic acid such as maleic acid with the known NaOH solution, the graph would show two separate inflections — representing the neutralization of each hydrogen — assuming the pKa values differ by 4 or more pK units (see Figure 2). The dissociation of a diprotic acid occurs in two separate steps ... 

Ka2. °r even < K 2. Such models are mathematically similar to the monoprotic model, since the diprotic model becomes similar to a monoprotic model if the acidity constants in the diprotic acid model are such that the neutral XOH group is insignificant in the material balance equations. 

The acid is a colorless moderately strong diprotic acid which gives anions 204 and HC204 with log Kp values of 4.3 and 1.2. Neutralization of the acid with bases produces oxalate and hydrogen oxalate salts which are white unless a colored cation is involved. Most of these salts are insoluble except those of the alkali metal cations. The acid and oxalates can be readily oxidized to CO2 andHOHbyMn04 and Cr04, but lesser oxidants maybe... 

The isoelectric pH of a polyprotic compound is that pH at which the average charge of all species is 0. For a diprotic amino acid whose amphiprotic form is neutral, the isoelectric pH is given by pH = (pK + pK2). The isoionic pH of a polyprotic species is the pH that would exist in a solution containing only the ions derived from the neutral polyprotic species and from H20. For a diprotic amino acid whose amphiprotic form is neutral, the isoionic pH is found from [H + ] = VC / F + K K )l(Ki + F), where F is the formal concentration of the amino acid. 

The protonated form of a neutral amino acid such as alanine is a diprotic acid, H2A+, with two acid dissociation constants, one for the -NH3 + group and one for the -CO2H group. 

The most important equilibria are those in which one of the two species is ionized, while the other is neutral. In many situations in RPLC both the monovalent and di- (tri-, etc.) valent ions have negligible capacity factors in comparison with the neutral molecule. Therefore, often all but one of the dissociation constants of an oligovalent species can be neglected. Equations for the influence of the pH on the retention of diprotic and oligoprotic substances can be found in ref. [316], p.239 et seq.. 

The correct answer is (D). This problem is another neutralization problem, but this time the acid is a diprotic acid. As a result, each mole of H2S04 will yield two moles of hydrogen ions. The calculation is as follows ... 

If Product M, a diprotic base, is to be analyzed in its neutral form, the higher of Product M (which is 5.3) needs to be considered because the other of 3.3 is less basic. Let us use to try to determine at what wpH the analyte would be in its neutral form at eluent conditions of 30v/v% MeCN and 70 v/v% acidic buffer. 

Nomenclature of Acids, Bases, and Salts. Acids with 1, 2, and 3 replaceable hydrogen atoms are called monoprotic, diprotic, and tri protic acids, respectively, and bases with 1, 2, and 3 replaceable hydroxide groups are called rnonohydroxic, dihydroxic, and trihydroxic bases. Salts such as Na.SO which result from complete neutralization... 

Acids. Acidic oxides, acid anhydrides. Bases, basic oxides. Neutralization—hydrogen ion plus hydroxide ion. Hydronium ion. Equivalent weights of acids and bases. Normality. Monoprotic, diprotic, and triprotic acids. Monohy-droxic, dihydroxic, and trihydroxic bases. 

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. 

Sulfuric acid is a neutral diprotic acid H2SO4, -- -r 4,... 

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

Table 15.5 shows the ionization constants of several diprotic acids and one polyprotic acid. For a given acid, the first ionization constant is much larger than the second ionization constant, and so on. This trend is reasonable because it is easier to remove a ion from a neutral molecule than to remove another H+ from a negatively charged ion derived from the molecule. 

A 5.00-g quantity of a diprotic acid was dissolved in water and made up to exactly 250 mL. Calculate the molar mass of the acid if 25.0 mL of this solution required 11.1 mL of 1.00 M KOH for neutralization. Assume that both protons of the acid were titrated. 

Ss is the solubility of the neutral salt of the diprotic acid or base, respectively. Other symbols are as used in the text. ... 

A 6.50-g sample of a diprotic acid requires 137.5 mL of a 0.750 AT NaOH solution for complete neutralization. Determine the molar mass of the acid. 

Some acids have more than one dissociable proton, and are called polyprotk acids. Sulfuric acid, H2SO4, and carbonic acid, H2CO3, are diprotic acids, phosphoric acid, H3PO4, is a triprotic acid. Other diprotic acids such as succinic, fumaric, and malic acids and the triprotic acid, citric acid, are important components of intermediary metabolism. In the case of carbonic acid, 1 mol of the acid can neutralize 2 mol of KOH ... 

In this experiment, you will standardize (determine precisely the concentration) a solution of sodium hydroxide, NaOH, using oxalic acid dihydrate, H2C204 2H20, as a primary standard acid. A primary standard acid is a solid acid whose mass is an accurate measure of the number of moles of protons the acid will furnish. Oxalic acid, H2C2O4, is a diprotic acid and provides two reactive protons per molecule according to the following net ionic equation for the neutralization reaction. 

Succinic acid (H2C4H5O4), which we will denote H2SUC, is a biologically relevant diprotic acid with the structure shown below. It is closely related to tartaric acid and malic acid (Figure 16.1). At 25 °C, the acid-dissociation constants for succinic acid are = 6.9 X 10 and Ff 2 = 2.5 X 10 . (a) Determine the pH of a 0.32 M solution of HjSuc at 25 °C, assuming that only the first dissociation is relevant, (b) Determine the molar concentration of Suc in the solution in part (a), (c) Is the assumption you made in part (a) justified by the result from part (b) (d) Will a solution of the salt NaHSuc be acidic, neutral, or basic ... 

A 15.0-mL sample of an oxalic acid solution requires 25.2 mL of 0.149 Af NaOH for neutralization. Calculate the volume of a 0.122 Af KMn04 solution needed to react with a second 15.0-mL sample of the oxalic acid solution. Hint Oxalic acid is a diprotic acid. See Problem4.95 for redox equation.)... 

Several aspects of these equilibria are notable. First, although carbonic acid is a diprotic acid, the carbonate ion is unimportant in this system. Second, one of the components of this equilibrium, CO2, is a gas, which provides a mechanism for the body to adjust the equilibria. Removal of CO2 via exhalation shifts the equilibria to the right, consuming H ions. Third, the buffer system in blood operates at a pH of 7.4, which is fairly far removed from the pK i value of H2CO3 (6.1 at physiological temperatures). In order for the buffer to have a pH of 7.4, the ratio [base]/[acid] must have a value of about 20. In normal blood plasma the concentrations of HCOs and H2CO3 are about 0.024 M and 0.0012 M, respectively. As a consequence, the buffer has a high capacity to neutralize additional acid, but only a low capacity to neutralize additional base. 

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