Acid-base titration curves sketching

Sketching an Acid—Base Titration Curve To evaluate the relationship between an equivalence point and an end point, we only need to construct a reasonable approximation to the titration curve. In this section we demonstrate a simple method for sketching any acid-base titration curve. Our goal is to sketch the titration curve quickly, using as few calculations as possible. 

Now that we know something about EDTA s chemical properties, we are ready to evaluate its utility as a titrant for the analysis of metal ions. To do so we need to know the shape of a complexometric EDTA titration curve. In Section 9B we saw that an acid-base titration curve shows the change in pH following the addition of titrant. The analogous result for a titration with EDTA shows the change in pM, where M is the metal ion, as a function of the volume of EDTA. In this section we learn how to calculate the titration curve. We then show how to quickly sketch the titration curve using a minimum number of calculations. 

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... 

Where Is the Equivalence Point In discussing acid-base titrations and com-plexometric titrations, we noted that the equivalence point is almost identical with the inflection point located in the sharply rising part of the titration curve. If you look back at Figures 9.8 and 9.28, you will see that for acid-base and com-plexometric titrations the inflection point is also in the middle of the titration curve s sharp rise (we call this a symmetrical equivalence point). This makes it relatively easy to find the equivalence point when you sketch these titration curves. When the stoichiometry of a redox titration is symmetrical (one mole analyte per mole of titrant), then the equivalence point also is symmetrical. If the stoichiometry is not symmetrical, then the equivalence point will lie closer to the top or bottom of the titration curve s sharp rise. In this case the equivalence point is said to be asymmetrical. Example 9.12 shows how to calculate the equivalence point potential in this situation. 

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

The methylol derivatives are stronger acids (weaker bases) than are the original unsubstituted amino groups. In other words, the pKo value for the substituted amino acid is lower than the pifo, value for the original amino acid. The titration curves are sketched in Figure 1-7. Note that formaldehyde has no effect on the amounts of KOH required to titrate the amino acid to pKa, pKo (or pKi,), and the equivalence points. Also note that only the pK value is shifted formaldehyde has no effect on the a-COOH group. 

The proton conditions of equations 48 and 49 correspond to the two equivalence points in acid-base titration systems. The half-titration point is usually (not always) given by pH = pAT. Thus the qualitative shape of the titration curve can be sketched readily along these three points (Figure 3,3a). 

Sketch titration curves for the following acid-base titrations (a) HCl versus NaOH, (b) HCl versus CH3NH2, (c) CH3COOH versus NaOH. In each case, the base is added to the acid in an Erlenmeyer flask. Your graphs should show pH on the y-axis and volume of base added on the x-axis. 

Where Is the Equivalence Point We have already learned how to calculate the equivalence point for the titration of a strong acid with a strong base, and for the titration of a weak acid with a strong base. We also have learned to sketch a titration curve with a minimum of calculations. Can we also locate the equivalence point without performing any calculations The answer, as you may have guessed, is often yes ... 

Sketching a Redox Titration Curve As we have done for acid-base and complexo-metric titrations, we now show how to quickly sketch a redox titration curve using a minimum number of calculations. 

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. 

We can just sketch approximate titration curves of pH vs. percent of titration, since we do not have the concentration of the acid or the base, or the volume of solution being titrated. We can, however, precisely determine the pH at the half-equivalence point [mid-way between untitrated and completely titrated for a weak acid (or base)] this is equal to the pof the weak acid (or pOH = pATb of the weak base). Further, if we assume all solutions are 1.00 M, we can determine the pH at each equivalence point. For a weak base, the pH at the equivalence point equals -log >/0.50(ATa). For a weak acid, the pH at the... 

On the same graph, sketch pH titration curves for titration of (1) a strong acid with a strong base and (2) a weak acid with a strong base. How do the two curves differ with respect to the following ... 

Sketch the titration curve for the titration of a generic weak base B with a strong acid. The titration reaction is... 

The titration curve for Tricine (base) showing the position of the buffer is sketched in Figure 1-3. The curve is shown for the titration of Tricine conjugate base with H. The curve for the titration of Tricine conjugate acid with OH" would be the mirror image of that shown. The pH of the buffer is less than pK. Therefore, [Tricine ] > [Tricine°], as shown below. 

Roughly sketch the titration curve (pH versus volume) that you would expect if you titrated a weak base with a strong acid. Mark the equivalence point. 

Make a rough sketch of the titration curve expected for the titration of a strong acid with a strong base. What determines the pH of the solution at the following points ... 

Sketch the titration curve of a weak acid versus a strong base like the one shown in Ligure 16.4. On your graph indicate the volume of base used at the equivalence point and also at the half-equivalence point, that is, the point at which half of the acid has been neutralized. Show how you can measure the pH of the solution at the half-equivalence point. Using Equation (16.4), explain how you can determine the pK, of the acid by this procedure. 

Sketch the titration curve for a weak acid titrated by a strong base. When performing calculations concerning weak acid-strong base titrations, the general two-step procedure is to solve a stoichiometry problem first, then to solve an equilibrium problem to determine the pH. What reaction takes place in the stoichiometry part of the problem What is assumed about this reaction ... 

Mathematical Sketch a titration curve for aspartic acid, and indicate the p values of all titratable groups. Also indicate the pH range in which the conjugate acid-base pair +1 Asp and 0 Asp will act as a buffer. 

A Make a rough sketch of the titration curve expected for the titration of a weak monoprotic acid with a strong base. What determines the pH of the solution at the following points (a) no base added (b) half-equivalence point (the point at which one-half of the titrant volume required to reach the equivalence point has been added) ... 

Use Figures 2.7a and 2.7b to sketch the pH curve of a strong acid being titrated by a weak base. 

Sketch the titration curve of a weak acid with a strong base like the one shown in Figure 17.4. On your graph, indicate the volume of base used at the equivalence point and also at the half-equivalence... 

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