Acetic acid conductometric titration

The quantitative analysis procedure involves gravimetric detn of the HMX on a moisture-free basis after benzene extraction of, and differential detn of TNT. Moisture content is detd by conductometric titration of sample in an acetic-sulfuric acid suspension. Acetone insoluble matter is determined gravimetrically... 

A polyvinyl acetate latex prepared by semi-continuous polymerization at 55° using a polymethacrylic acid-nonylphenol-poly-ethoxylate phosphate ester emulsifier and sodium persulfate-sodium formaldehyde sulfoxylate initiator (23). The latex was cleaned by ion exchange and serum replacement using both Nuclepore and Pellicon membranes, and the cleaned latex and serum fractions were analyzed by conductometric titration. In addition, the dried films were extracted with water and organic solvents, and the extracts were analyzed by infrared spectroscopy and thermo-gravimetric analysis. 

Fig. 6.7. Conductometric titration curves of basic components extracted from engine oil CB SAE 30 into glacial acetic acid. Curve 1 -fresh oil, 2 - after 45 h of use, 3 - after 625 h of use (Pawlak et al.,...

Fig. 1. Curves of conductometric (1,3) and potentiometric (2) titrations of aqueous solutions of MAn/AA copolymer (2, 3) and acetic acid with polyvinylpyrrolidone solution (l)21,67j...

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...

The addition of excess calcium acetate to purified cellulosic material suspended in water, followed by titration of the liberated acetic acid, was suggested by L(idtke. From the 0.1% carboxyl content obtained, a D.P. value of 277 was calculated for the cellulosic material employed. This method has been studied further and comparative data with the earlier conductometric titration procedure have been presented by Heymann and Rabinov, by Kenyon and coworkers, and by Sookne and Harris. The latter workers report that electrodialyzed depectin-ized cotton has a carboxyl content of 0.045% or a D.P, of 616. An iodometric titration procedure for estimating carboxyl groups in cellulosic materials has also been described by Ltidtke. The procedure involves a thiosulfate titration of the iodine liberated from a mixture of potassium iodate and potassium iodide by the carboxyl groups of the cellulosic material. The carboxyl content determined by this method agreed well with that obtained by the calcium acetate method. 

In conductometric titrations, a change in conductance is caused after the endpoint owing to the increase in concentration of the mobile hydroxide ion. Very weak acids (such as boric acid) and moderately weak acids (such as acetic acid) can be titrated using conductometric titration. 

If the titrant is a weak electrolyte (such as ammonia), the curve is essentially horizontal past the equivalence point, which causes less uncertainty to the extrapolation of a curve. In titration of a weak base, such as acetate ion, with a strong acid, a salt and undissociated acetic acid are formed. After the endpoint is passed, a sharp rise in conductance attends the addition of excess hydronium ions. Salts whose acidic or basic character is too weak to give satisfactory endpoints with indicator are conveniently titrated with the conductometric method. The conductometric titration of a mixture of two acids that differ in degree of dissociation is frequently more accurate than a potentiometric titration. 

The following is intended only as a demonstration of the method of conductometric titration. Prepare a 0.05 M solution of lead acetate and a standardised 1.00 M solution of sulphuric acid. Pipette 50.0 mL of the acetate solution into a conductometric titration cell. 

Conductometric methods are useful in the titration of mixtures of strong and weak acids. Thus an analysis of a mixture of acetic and hydrochloric acids can be carried out with fair accuracy. The result of such a titration is shown in Fig. 7, also due to Kolthoff. The added base first reacts with the strong acid producing a break in the curve at the equivalence point, followed by another break in the curve when the weak acid is neutralized. As shown, the first intersection is far from being sharp. This is due to the commencement of the ionization of the acetic acid before all the hydrochloric acid has disappeared. However, the equivalence point can be established by extending the straight portions of the lines as indicated. 

Figure 14 Conductometric titration curves of various acids by sodium hydroxide. Curve 1 represents a strong acid, and curve 5 an extremely weak one, while the others are intermediate. The acids are (1) hydrochloric acid, (2) dichloroacetic acid, (3) mon-ochloroacetic acid, (4) acetic acid, and (5) boric acid. (From Ewing GW (1985) Instrumental Methods of Chemical Analysis, 5th edn., p. 337. New York McGraw-Hill.)...

Conductometric titration of alpha acids was in the not so distant past the most common procedure in the brewery laboratories. In this method, a suitable solution of an extracted hop or of the dissolved hop extract is titrated with a solution of lead(ll) acetate and the conductivity plot allows deduction of the results. Many contributions on the conductometry of alpha acids have appeared in the literature. The titration curve can be influenced substantially by changing the titration medium, as we found out for a number of mixed solvents (10), Current methods add either a base or dimethylsulfoxide to improve the determination of the titration endpoint. The Analysis Committee of the European Brewery Convention repeatedly organized collaborative trials to evaluate hop conductometric analysis. The efforts of a Working Group on Hop... 

Conductometry is a very attractive method for alpha acids analysis, because of the low cost of the necessary instrumentation. One of the major causes of trouble is that other compounds can be present which also react with lead(ll) acetate. Iso-alpha acids for example consume half the amount of lead(ll) acetate as the same weight of alpha acids would do. Some oxidation products of the alpha and beta acids can also consume lead(ll) acetate. Whether or not they do so depends on the titration medium. At the 1970 EBC Interlaken meeting it was shown that addition of water, even in traces, changes the conductometric titration curve drastically (5). It is even possible to derive two analysis figures from one titration curve, one for iso-alpha acids and oxidation products, and one for alpha acids. The results are however not sufficiently reliable for... 

The conductometric method of titration is of particular service when the reaction is the replacement of the anion of the salt of a weak acid with the anion of a strong acid. Thus, for example, in the titration of sodium acetate with hydrochloric acid the weak acid is liberated and... 

Originally a-acids were estimated gravimetrically as their lead salts (see [22]) but this lengthy procedure has been superceded by conductometric estimation of the end point in the titration of a-acids against lead acetate. Typically [24, 25, 26] a toluene extract of hops is diluted with methanol and the conductivity measured. Small aliquots (0-2 ml) of a methanolic solution of lead acetate (2 or 4 %) are added and the conductivity measured after each addition. A graph is plotted of conductivity against volume of lead acetate solution added and the end point determined from the intersection of two straight lines (Fig. 13.3). The curves may show different shapes in other solvents [27]. 

Likens and Nickerson were the first to describe the addition of 1 % pyridine to the conductometric alpha acids titration medium (6). This amount is however insufficient to produce a titration curve with a sharp inflection endpoint this requires about 20 % pyridine. Pyridine is not only an obnoxious solvent, it is also a fairly dangerous one. The problems of disposing of the titration waste are thus not to be underestimated. Another reason to prefer DMSO is that upon addition of pyridine, other groups of alpha and beta acids oxidation products become lead(ll) acetate active, which leads to too high results. 

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