Buffers acid-base titration

Chapter 14, Acids and Bases, discusses acids and bases and their strengths, conjugate acid-base pairs, the dissociation of weak acids and bases and water, pH and pOH, and buffers. Acid-base titration uses the neutralization reactions between acids and bases to calculate quantities of acid in a sample. Section 14.9, Acid-Base Properties of Salt Solutions, has been deleted. Combining Ideas from Chapters 11,12,13, and 14 follows as an interchapter problem set. 

Other methods employ a microplate format followed by fast HPLC. Some researchers approach the determination from a different perspective. For example, an alternative method for ionizable substances is the pSol determination based on an acid-base titration.25 26 Kinetic solubility determinations involve determining the concentration of the compound in the buffer of interest when an induced precipitate first appears. 

You learned about acids and bases in your previous chemistry course. In this chapter, you will extend your knowledge to learn how the structure of a compound determines whether it is an acid or a base. You will use the equilibrium constant of the reaction of an acid or base with water to determine whether the acid or base is strong or weak. You will apply your understanding of dissociation and pH to investigate buffer solutions solutions that resist changes in pH. Finally, you will examine acid-base titrations that involve combinations of strong and weak acids and bases. 

An acid-base titration is a method that allows quantitative analysis of the concentration of an unknown acid or base solution. In an acid-base titration, the base will react with the weak acid and form a solution that contains the weak acid and its conjugate base until the acid is completely neutralized. The following equation is used frequently when trying to find the pH of buffer solutions. 

The amphoteric nature of wool was demonstrated in the early studies of Speakman and Hirst (1933), Elod (1933), and in particular by the complete acid-base titration curve obtained by Speakman and Stott (1934). Even earlier attempts had been made to determine the isoelectric point of wool by the methods indicated in Table XXIII. Some variation in the isoelectric point is to be expected because the pH at which the net charge, including bound ions, is zero depends on the nature and concentrations of ions in the aqueous environment. For example, Sookne and Harris (1939) have shown that the early electrophoretic value of Harris (1932) was affected by the absorption of phthalate ions from the buffer solutions. With acetate buffer they obtained values of 4.2 and 4.5 for powdered wool and cortical cells, respectively. The isoelectric points listed in Table XXIII are... 

It is important to know the dissociation constant of an indicator in order to use it properly in acid-base titrations. Spectrophotometry can be used to measure the concentration of these intensely colored species in acidic versus basic solutions, and from these data the equilibrium between the acidic and basic forms can be calculated. In one such study on the indicator wj-nitrophenol, a 6.36 X 10 M solution was examined by spectrophotometry at 390 nm and 25°C in the following experiments. In highly acidic solution, where essentially all the indicator was in the form HIn, the absorbance was 0.142. In highly basic solution, where essentially all of the indicator was in the form In , the absorbance was 0.943. In a further series of experiments, the pH was adjusted using a buffer solution of ionic strength I, and absorbance was measured at each pH value. The following results were obtained ... 

Evaluate the importance of a buffer in controlling pH. Design strategies for doing acid-base titrations, and calculate results from titration data. 

Buffers to Regulate pH The Acid-Base Chemistry of Antacids Stoichiometry Revisited Acid-Base Titrations MiniLab 15.2 What does a buffer do ... 

In this chapter we have encountered the most important analytical aspects of acids and bases (a) their individual speciation, as described by the mass action law, and as reflected in the distribution and logarithmic concentration diagrams, (b) their buffer action, and (c) their neutralization, as exploited in acid-base titrations. 

Having discussed buffer solutions, we can now look in more detail at the quantitative aspects of acid-base titrations, which we discussed briefly in Section 4.6. Recall that titration is a procedure for determining the concentration of a solution using another... 

The acidity or basicity of a solution is frequently an important factor in chemical reactions. The use of buffers of a given pH to maintain the solution pH at a desired level is very important. In addition, fundamental acid-base equihbria are important in understanding acid-base titrations and the effects of acids on chemical species and reactions, for example, the effects of complexation or precipitation. In Chapter 6, we described the fundamental concept of equilibrium constants. In this chapter, we consider in more detail various acid-base equilibrium calculations, including weak acids and bases, hydrolysis, of salts of weak acids and bases, buffers, polyprotic acids and their salts, and physiological buffers. Acid-base theories and the basic pH concept are reviewed first. 

In Chapter 4, we discussed the acid-base titration as an analytical method. Let s re-examine it, this time tracking the change in pH with an acid-base titration curve, a plot of pH vs. volume of titrant added. The behavior of an acid-base indicator and its role in the titration are described first. To better understand the titration process, we apply the principles of the acid-base behavior of salt solutions (Section 18.7) and, later in the section, the principles of buffer action. 

Complexometric titration curves can be better characterized when we can describe slopes of curves. The change of pM (= -npL) with Vl and its reciprocal will help us understand metal buffer behavior and sharpness of titrations, just as they did with acid-base titrations. The mathematical... 

An alternative to the acid-base titration is to neutralize the acid and raise the pH with a buffer, followed by addition of reagents that form a colored product with NH3. The absorbance of the colored product gives the concentration of NH3 from the digestion. 

In the case of strong polyelectrolytes, the number of ionized units corresponds to the number of dissociable ionic units (see Manning condensation) and is independent of the pH. Eor weak polyelectrolytes, the number of ionized units at a given pH is dependent on the p/sTa- Erom acid/base titration, their p/sTa as well as buffering capacity (illustrated by plotting the pH of a solution containing a polymer as a function of the volume of acid added) can be determined. The following equation reported by Patchomik et al. can be used to determine the number of ionized units, i.e., the protonation state of a polycation, at a specific pH [82] ... 

---