Acid-base titrations strong

The utility of acid-base titrimetry improved when NaOH was first introduced as a strong base titrant in 1846. In addition, progress in synthesizing organic dyes led to the development of many new indicators. Phenolphthalein was first synthesized by Bayer in 1871 and used as a visual indicator for acid-base titrations in 1877. Other indicators, such as methyl orange, soon followed. Despite the increasing availability of indicators, the absence of a theory of acid-base reactivity made selecting a proper indicator difficult. 

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... 

Equivalent Weights Acid-base titrations can be used to characterize the chemical and physical properties of matter. One simple example is the determination of the equivalent weighf of acids and bases. In this method, an accurately weighed sample of a pure acid or base is titrated to a well-defined equivalence point using a mono-protic strong acid or strong base. If we assume that the titration involves the transfer of n protons, then the moles of titrant needed to reach the equivalence point is given as... 

Titrimetric methods have been developed using acid-base, complexation, redox, and precipitation reactions. Acid-base titrations use a strong acid or strong base as a titrant. The most common titrant for a complexation titration is EDTA. Because of their... 

Alkalinity is measured by acid-base titration with methylorange or phe-nolphthalein as indicator. Phenolphthalein changes color at pH 8.3, whereas methylorange changes color at pH 4.3. At pH 8 the neutralization of the strong alkali ingredients like NaOH is essentially complete. Further reduction of the pH to 4 will also measure carbonates and bicarbonates. Colorimetric tests and glass electrode systems are used to determine pH. 

When an acid in solution is exactly neutralized with a base the resulting solution corresponds to a solution of the salt of the acid-base pair. This is a situation which frequently arises in analytical procedures and the calculation of the exact pH of such a solution may be of considerable importance. The neutralization point or end point in an acid-base titration is a particular example (Chapter 5). Salts may in all cases be regarded as strong electrolytes so that a salt AB derived from acid AH and base B will dissociate completely in solution. If the acid and base are strong, no further reaction is likely and the solution pH remains unaffected by the salt. However if either or both acid and base are weak a more complex situation will develop. It is convenient to consider three separate cases, (a) weak acid-strong base, (b) strong acid-weak base and (c) weak acid-weak base. 

To select an indicator for an acid-base titration it is necessary to know the pH of the end point before using equation (5.5) or standard indicator tables. The end point pH may be calculated using equations (3.27), (3.29) or (3.30). Alternatively, an experimentally determined titration curve may be used (see next section). As an example, consider the titration of acetic acid (0.1 mol dm 3), a weak acid, with sodium hydroxide (0.1 mol dm-3), a strong base. At the end point, a solution of sodium acetate (0.05 mol dm 3) is obtained. Equation (3.28) then yields... 

The end point in a titration is a little different from the end of a reaction. What is desired is to know when all the add is titrated. This happens when the titration curve, shown in Figure 10.1, reaches its maximum slope. This change occurs at a pH of 7 for a typical strong acid-base titration), but occurs at pH... 

This is the basis for a common method for the determination of ammonia in soil.1 Soil is suspended in water and placed in a Kjeldahl flask. The suspension is made basic by the addition of a strong (5-50%) sodium hydroxide solution, and the flask is immediately attached to a steam distillation setup. Steam distillation of the suspension carries the released ammonia to an Erlenmeyer flask, catching the distillate in a standardized acid solution that is subsequently back titrated via acid-base titration. The amount of ammonia in soil can be calculated from the end point of the titration. This procedure is similar to a standard Kjeldahl determination and can be carried out using the same equipment, although no digestion is needed. 

FIGURE 5.1 Acid-base titration curves (a) 0.10 M HCI (strong acid) titrated with 0.10 M NaOH (strong base), (b) 0.010 M HCI titrated with 0.010 M NaOH, and (c) 0.10 M acetic acid (weak acid) titrated with 0.10 M NaOH. 

FIGURE 5.2 A family of acid-base titration curves for a 0.10 M strong acid (HC1) and three weak acids, as indicated (0.10 M each), titrated with 0.10 M NaOH (strong base). HAc is a representation of acetic acid. 

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. 

In this section, you examined acid-base titration curves for combinations of strong and weak acids and bases. You may have noticed the absence of a curve for the reaction of a weak acid with a weak base. A weak acid-weak base titration curve is difficult to describe quantitatively, because it has competing equilibria. You may learn about this curve in future chemistry courses. 

If the profile of the observed or the intrinsic rate constant plotted against pH resembles the profile for an acid-base titration curve, this strongly suggests that one of the reactants is involved in an acid-base equilibrium in that pH range. Such behavior is ftiirly common and is illustrated by the second-order reaction between the Co(II)-trien complex and O2 (Fig. 1.12). The limiting rate constants at the higher and low acidities correspond to the acidic and basic forms of the Co(II) reactant, probably. 

Elemental composition B 17.50%, H 4.88%, O 77.62%. Boric acid may be analysed by adding calcium chloride (in excess) and sorbitol or mannitol to its solution, followed by acid-base titration using a strong base to phenolph-thalein endpoint. Elemental boron may be analyzed by AA or ICP spectrophotometry. 

The strength of nitric acid can be determined by acid-base titration against a standard solution of a strong base such as NaOH using a color indicator, or by potentiometric titration using a pH meter. Nitrate ion, NO3 in its aqueous solution, may be measured with a nitrate ion-selective electrode or by ion chromatography following appropriate dilution. 

Elemental composition Na 43.39%, C 11.33%, O 45.29%. Aqueous solution of sodium carbonate is strongly alkahne and its normahty can be measured by acid-base titration. Sodium content can be measured by AA, ICP, and other instrumental analyses. Carbonate anion can be measured by ion chromatography or from carbon dioxide hberated when the salt is treated with dilute... 

For the titration of a strong base with a weak acid, the equivalence point is reached when the pH is greater than 7. The half equivalence point is when half of the total amount of base needed to neutralize the acid has been added. It is at this point that the pH = pK of the weak acid. In acid-base titrations, a suitable acid-base indicator is used to detect the endpoint from the change of colour of the indicator used. An acid-base indicator is a weak acid or a weak base. The following table contains the names and the pH range of some commonly used acid-base indicators. 

You would not choose a weak acid to titrate a Clearest results are achieved with the strongest oxidizing and reducing agents. The same rule weak base, because the break at Ve would applies to acid-base titrations where strong-acid or strong-base titrants give the sharpest... 

As a final example of an acid-base titration, let s consider the gradual addition of NaOH to the protonated form of the amino acid alanine (H2A+), a substance that acts as a diprotic acid. Amino acids (which are discussed in more detail in Chapter 24) are both acidic and basic and can be protonated by strong acids such as HC1, yielding salts such as H2A+C1 . The protonated form of the amino acid has two... 

A pH titration curve is a plot of the pH of a solution as a function of the volume of base (or acid) added in the course of an acid-base titration. For a strong acid-strong base titration, the titration curve exhibits a sharp change in pH in the region of the equivalence point, the point at which stoichiometri-... 

Acid-base titration involves a neutralization reaction between an acid and a soluble base. The reactants may be a strong acid and a strong base, a strong acid... 

Fig. 13.2. Methods for determining the equivalence point of a potentiometric titration curve (including acid-base titrations), (a) First derivative (b) Second derivative (c) Gran plot for titration of a strong acid with a strong base Vx is the initial volume of acid and V the volume of base added.

An acid-base titration is a procedure that is typically used to determine the concentration of an unknown acid or base solution. In a titration, a strong or base or known concentration is added to a base or acid of unknown concentration. An indicator solution is typically utilized to mark the equivalence point, or the point at which the stoichiometric amounts of acid and base are equivalent. 

You may be familiar with acid-base titration that use phenolphthalein as the endpoint indicator. You might not have noticed, however, what happens when a solution that contains phenolphthalein in the presence of excess base is allowed to stand for a few minutes. Although the solution initially has a pink colour, it gradually turns colourless as the phenolphthalein reacts with the OH- ion in a strongly basic solution. 

Titration is a technique for determining either the concentration of a solution of unknown molarity or the number of moles of a substance in a given sample. A chemical reaction is used for this purpose, and the reaction must be fast, be complete, and have a determinable end point. The reactions of strong acids and bases generally meet these criteria, and acid-base titrations are among the most important examples of this technique. 

Salt formation generally favors the quinoid form and these salt solns are usually brightly Qolored. Presence of strong acids favors the colorless phenol form. Because of these color changes, nitrophenols have been used as indicators in acid-base titrations... 

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