Titration of acetic acid

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... 

In the process of a weak acid or weak base neutralization titration, a mixture of a conjugate acid-base pair exists in the reaction flask in the time period of the experiment leading up to the inflection point. For example, during the titration of acetic acid with sodium hydroxide, a mixture of acetic acid and acetate ion exists in the reaction flask prior to the inflection point. In that portion of the titration curve, the pH of the solution does not change appreciably, even upon the addition of more sodium hydroxide. Thus this solution is a buffer solution, as we defined it at the beginning of this section. 

The function NewtonRaphson.m is very general and can easily be adapted for any titration. The potentiometric titration of acetic acid with NaOH solution serves as an additional example of its usage. 

Figure 3-13. Potentiometric pH titration of acetic acid with strong base.

The function Data EqAH2, m simulates the pH-titration of a weak diprotic acid, AH2, in acid excess, with a strong base. The computation of the equilibria is similar to the examples Eql. m and Eq2. m given in the Chapters Example General 3-Component Titration (p.56) and Example pH Titration of Acetic Acid (p.58). From the present point of view, the important aspect is that all variables are collected in one structure s. The model is now stored in s.Model, the logP values in s. log beta, etc. Importantly, all the information contained in s is returned to the invoking programs. 

Titration of acetic acid with sodium hydroxide pH versus ml of NaOH. 

PROBLEM 6.16.4. Repeat the titration of acetic acid, but now starting with 50 mL of 1M acetic acid and adding y mL of 1M NaOH. 

Curve (b) shows the titration of acetic acid, K, 1.75 x 10"1 mol dm"1 at two different concentrations. The initial additions of OH" establish a buffer solution in which the H30+ concentration is only slowly reduced. The resulting fall in conductance is increasingly counteracted by the addition of Nr and the formation of CHjCOO" thus leading to a minimum in the cur e. After the equivalence-point, there is a more rapid increase due to t -addition of excess OH" and Na+. Concentrated solutions of weak acids gi more pronounced changes of slope at the equivalence point than dilu solution. The change in slope is well defined for very weak acids, curve (c. 

Figure 6.19. Conductometric titration curves (a) Titration of strong acid with NaOH. (b) Titration of acetic acid, K, = 1.75 x 10 3 mol dm" with NaOH. (c) Titration of boric acid Jf,= 6x 10" io mol dm" J with NaOH. (d) Titration...

Titrimetric Methods. These methods involve the titration of acetic acid liberated by the hydrolysis of acetylcholine, which is normally ac-comphshed with a pH-stat so that a constant pH is maintained. The advantages of these methods over the ApH methods are that the measured... 

What indicator would you choose for the titration of acetic acid with potassium hydroxide ... 

Figure 14-5 Curve for the titration of acetic acid with sodium hydroxide. Curve A 0.1000 M acid with 0.1000 M base. Curve B 0.001000 M acid with 0.001000 M ba.se.

Fig. 6. The Titration of Acetic Acid, at Different Dilutions, with Sodium Hydroxide.

The reaction must be stoichiometric. That is, there must be a well-defined and known reaction between the analyte and the titrant. In the titration of acetic acid in vinegar with sodium hydroxide, for example, a well-defined reaction takes place ... 

Two important conclusions can be drawn from a comparison of the titration of 50.0 mL of 0.1 A/acetic acid covered earlier in this section and that of 50.0 mL of 0.1 AT hydrocyanic acid analyzed in Example 15.9. First, the same amount of 0.1 AT NaOH is required to reach the equivalence point in both cases. The fact that HCN is a much weaker acid than HC2H3O2 has no bearing on the amount of base required. It is the amount of acid, not its strength, that determines the equivalence point. Second, the pH value at the equivalence point is affected by the acid strength. For the titration of acetic acid, the pH at the equivalence point is 8.72 for the titration of hydrocyanic acid, the pH at the... 

Reflect and Apply In Section 2.4 we said that at the equivalence point of a titration of acetic acid, essentially all the acid has been converted to acetate ion. Why do we not say that all the acetic acid has been converted to acetate ion ... 

Figure 84 shows the example of a titration of acetic acid with sodium hydroxide to illustrate how the titration error can be derived from a pH-logCi diagram. 

Fig. 84 Reading of the relevant concentration data ftom the pH-logCi diagram for estimation of the systematic titration errors in case of the titration of acetic acid = 0.1 mol L ) with...

Generating the titration curves for weak acids with NaOH. Figure 8.2 (note here, too, pH is in the unusual position as X-variable) illustrates the titration curves obtained by using Equation 8-2 for titrations of acetic acid of various concentrations with equal concentrations of NaOH. 

The use of qualitative information alone is not suf cient to correctly characterize an essential oil, and quantitative data are of extreme importance. Classical methods are generally focused on chemical groups and the assessment of quantitative information through titration is widely applied, for example, for the acidimetric determination of saponi ed terpene esters. Saponi cation can be performed with heat, and in this case, readily saponi ed esters are to be investigated, in the cold, and afterward, the alkali excess is titrated with aqueous hydrochloric acid thereafter, the ester number can be calculated. A further test is the determination of terpene alcohols by acetylating with acetic anhydride part of the acetic anhydride is consumed in the reaction and can be quanti ed through titration of acetic acid with sodium hydroxide. The percentage of alcohol can then be calculated. The latter method is applied when the alcoholic constituents of an essential oil are not well known in case these are established, the oil is saponi ed, and the ester number of the acetylated oil is calculated and used to estimate the free alcohol content. 

Example 6 At the equivalence point of a titration of acetic acid with NaOH. 2.500 mmoles of NaCaHjOj are in 125.0 ml of solution. For the acetate ion, Kb = 5.71 X 10 . Select an indicator suitable for this titration. 

We must use indicators whose color-change interval is located in basic pH values. Their choice depends on thepK value of the acid. For example, for the titration of acetic acid in the above conditions, pH = 8.7 at the equivalence point. Using phe-nolphthalein, thymolphthalein, and thymol blue is satisfactory. For the second acid (pKa 7.00), pH = 9.9 at the equivalence point, only thymolphthalein is satisfactory. (Recall that in this second example, the color-change interval is narrower than in the first one—see the curve s shape). For very weak acids (pKa > 7), no simple indicator can be used. Only some mixtures of judiciously chosen indicators can be used. This is due to the fact that the pH change at the equivalence point is very weak. The very deep reason behind this fact is that the neutralization reaction can no longer be considered quantitative (see Chap. 10). 

The gradual change near the equivalence point must be ascribed to the fact that the neutralization reaction is too equilibrated. This is the case when the couples HAi/Ai and HA2/A2 are too close to each other on the acidity scale. Reciprocally, when they are suflBciently far from each other, we can expect to achieve an accurate titration. The example of the titration of acetic acid (pATa=4.75) by ammonia pAra(NH4 ) = 9.21] is interesting to consider since it is on the border of satisfactory and nonsatisfactory titrations. Indeed, with 10 mol/L—solutions and with a pH-metric detection of the equivalence point, the titration error is about 0.5%. It is higher than that due to the graduation of the glassware (0.2%). However, it remains acceptable. The lack of precision is higher, by far, when neutralization indicators are used. 

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