Acids titration curves for

Most of the titratable charge in seawater is supplied by bicarbonate because its concentration is much greater than that of carbonate or any of the other weak bases in seawater, such as B(OH). A typical acid titration curve for a seawater sample is shown in Figure 15.7. If the titration is performed in an open container, initial addition of acid does not cause much of a drop in pH. During this phase of the titration, is readily consumed, first by carbonate (Eq. 5.57) and then by bicarbonate (Eq. 5.56). Most of the buffering is provided by bicarbonate because of its high concentration. Once most of the bicarbonate has been consumed, further addition of acid causes a rapid decline in pH. 

Figure 1.3 shows that the acid titration curve for a weak acid can be calculated from its pKs, and this raises the question as to how the pKs can be calculated from the titration curve. This can be done by first integrating equation 1.3-9 to obtain the natural logarithm of the binding potential P ... 

Interpretation of Acid Titration Curves for Proteins in the Presence and Absence of Ligand Binding Potential of Wyman References... 

The effects of salt concentration on the acid titration curve for wool are illustrated in Fig. 8. The broad isoelectric region observed in the absence of salt becomes less apparent with increasing salt concentration,... 

Figure 5.6 TTie carbonate distribution diagram of a solution with constant Cf = 2.5 x 10" M showing (a) the strong acid titration curve for the same solution from pH 12 to 3 and strong base titration curve between pH 3 and 12. Dashed straight lines in (b) indicate concentrations of H+ and OH", which are independent of Cj. Modified after V. L. Snoeyink and D. Jenkins, Water Chemistry. Copyright 1980 by John Wiley Sons, Inc. Used by permission of John Wiley Sons, Inc.

To calculate the buffer index of an aqueous system we begin by deriving the equation for the acidity titration curve for that system. For pure water we will assume the litrant is NaOH. The charge-balance equation is then simply... 

Laboratory studies on the evaluation and efficiency of stabilization processes were performed by Calmano et al. (1988) on Hamburg harbor mud, using acid titration curves for limestone and cement/fly ash stabilizers. Best results are attained with calcium carbonate, since the pH-conditions are not changed sigmficantly upon addition... 

In the overview to this chapter we noted that the experimentally determined end point should coincide with the titration s equivalence point. For an acid-base titration, the equivalence point is characterized by a pH level that is a function of the acid-base strengths and concentrations of the analyte and titrant. The pH at the end point, however, may or may not correspond to the pH at the equivalence point. To understand the relationship between end points and equivalence points we must know how the pH changes during a titration. In this section we will learn how to construct titration curves for several important types of acid-base titrations. Our... 

Sketch the titration curve for the titration of 50.0 mb of 0.100 M acetic acid with 0.100 M NaOH. This is the same titration for which we previously calculated the titration curve (Table 9.3 and Figure 9.6). 

This approach can be used to sketch titration curves for other acid-base titrations including those involving polyprotic weak acids and bases or mixtures of weak acids and bases (Figure 9.8). Figure 9.8a, for example, shows the titration curve when titrating a diprotic weak acid, H2A, with a strong base. Since the analyte is... 

Figure 9.8b shows a titration curve for a mixture consisting of two weak acids HA and HB. Again, there are two equivalence points. In this case, however, the equivalence points do not require the same volume of titrant because the concentration of HA is greater than that for HB. Since HA is the stronger of the two weak acids, it reacts first thus, the pH before the first equivalence point is controlled by the HA/A buffer. Between the two equivalence points the pH reflects the titration of HB and is determined by the HB/B buffer. Finally, after the second equivalence point, the excess strong base titrant is responsible for the pH. 

The principal limitation to using a titration curve to locate the equivalence point is that an inflection point must be present. Sometimes, however, an inflection point may be missing or difficult to detect, figure 9.9, for example, demonstrates the influence of the acid dissociation constant, iQ, on the titration curve for a weak acid with a strong base titrant. The inflection point is visible, even if barely so, for acid dissociation constants larger than 10 , but is missing when is 10 k... 

Titration curves for a weak acid with 0.100 M NaOH—(a) normal titration curve (b) first derivative titration curve ... 

Titration curve for 50.00 ml of 0.0500 M Fe + with 0.0500 M Ce + showing the range of f and volume of titrant over which the indicators ferroin and diphenylamine sulfonic acid are expected to change color. 

The scale of operations, accuracy, precision, sensitivity, time, and cost of methods involving redox titrations are similar to those described earlier in the chapter for acid-base and complexometric titrimetric methods. As with acid-base titrations, redox titrations can be extended to the analysis of mixtures if there is a significant difference in the ease with which the analytes can be oxidized or reduced. Figure 9.40 shows an example of the titration curve for a mixture of Fe + and Sn +, using Ce + as the titrant. The titration of a mixture of analytes whose standard-state potentials or formal potentials differ by at least 200 mV will result in a separate equivalence point for each analyte. 

Calculate or sketch (or both) qualitatively correct titration curves for the following acid-base titrations. 

The following data were collected with an automatic titrator during the titration of a monoprotic weak acid with a strong base. Prepare normal, first-derivative, second-derivative, and Gran plot titration curves for this data, and locate the equivalence point for each. 

Schwartz has published some hypothetical data for the titration of a 1.02 X ICr" M solution of a monoprotic weak acid (pXa = 8.16) with 1.004 X ICr M NaOH. " A 50-mL pipet is used to transfer a portion of the weak acid solution to the titration vessel. Calibration of the pipet, however, shows that it delivers a volume of only 49.94 ml. Prepare normal, first-derivative, second-derivative, and Gran plot titration curves for these data, and determine the equivalence point for each. How do these equivalence points compare with the expected equivalence point Comment on the utility of each titration curve for the analysis of very dilute solutions of very weak acids. 

Calculate or sketch (or both) the titration curves for 50.0 ml of a 0.100 M solution of a monoprotic weak acid (pfQ = 8) with 0.1 M strong base in (a) water and (b) a non-aqueous solvent with ffg = 10 . You may assume that the change in solvent does not affect the weak acid s pfQ. 

The titration of a mixture ofp-nitrophenol (pfQ = 7.0) and m-nitrophenol pK = 8.3) can be followed spectrophotometrically. Neither acid absorbs at a wavelength of 545 nm, but their respective conjugate bases do absorb at this wavelength. The m-nitrophenolate ion has a greater absorbance than an equimolar solution of the p-nitrophenolate ion. Sketch the spectrophotometric titration curve for a 50.00-mL mixture consisting of 0.0500 M p-nitrophenol and 0.0500 M m-nitrophenol with 0.100 M NaOH, and compare the curve with the expected potentiometric titration curves. 

The acidity of a water sample is determined by titrating to fixed end points of 3.7 and 8.3, with the former providing a measure of the concentration of strong acid, and the latter a measure of the combined concentrations of strong acid and weak acid. Sketch a titration curve for a mixture of 0.10 M HCl and 0.10 M H2CO3 with 0.20 M strong base, and use it to justify the choice of these end points. 

FIGURE 2.12 The titration curve for acetic acid. Note that the titration curve is relatively flat at pH values near the pK in other words, the pH changes relatively little as OH is added in this region of the titration curve. 

Titration is the analytical method used to determine the amount of acid in a solution. A measured volume of the acid solution is titrated by slowly adding a solution of base, typically NaOH, of known concentration. As incremental amounts of NaOH are added, the pH of the solution is determined and a plot of the pH of the solution versus the amount of OH added yields a titration curve. The titration curve for acetic acid is shown in Figure 2.12. In considering the progress of this titration, keep in mind two important equilibria ... 

FIGURE 2.14 The titration curve for phosphoric acid. The chemical formulas show the prevailing ionic species present at various pH values. Phosphoric acid (H3PO4) has three titratable hydrogens and therefore three midpoints are seen at pH 2.15 (p. i), pH 7.20 (p. 2). and pH 19.4 (p. 3). 

Typical values for pAlg are in the range of 9.0 to 9.8. At physiological pH, the a-carboxyl group of a simple amino acid (with no ionizable side chains) is completely dissociated, whereas the a-amino group has not really begun its dissociation. The titration curve for such an amino acid is shown in Figure 4.7. 

Draw an appropriate titration curve for aspartic acid, labeling the axes and indicating the equivalence points and the values. 

Below is the titration curve for the neutralization of 25 mL of a monoprotic acid with a strong base. Answer the following questions about the reaction and explain your reasoning in each case, (a) Is the acid strong or weak (b) What is the initial hydronium ion concentration of the acid (c) What is K, for the acid (d) What is the initial concentration of the... 

If the equation is evaluated at ratios of [A ]/[HA] ranging from 10 to 10 and the calculated pH values are plotted, the resulting graph describes the titration curve for a weak acid (Figure 2—4). 

Figure 2-4. Titration curve for an acid of the type HA. The heavy dot in the center of the curve indicates the p/fg 5.0.

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