Titratable organic acids

Phytochemistry Roots collected in the Toshkent region contained 1.16 % tannins and up to 2 % sugars. Stems contained 0.87 % tannins, up to 4 % sugars, 0.4 % titratable organic acids, and alkaloid traces. Leaves contain 1.74 % tannins, 0.53 % titratable organic acids, and alkaloid traces fruits contain up to 2 % sugars, 1.07 % titratable organic acids, and alkaloid traces (Khalmatov 1964). 

Oxalate Acid Number. A metal soap solution is treated with a measured excess of organic acid. Potassium oxalate solution is added to precipitate the metal and the total sample is back-titrated with alkaU to determine its acidity. Acidity is expressed ia acid number units, equivalent to mg KOH per g. A neutral soap gives a 2ero acid number, an acidic soap solution a positive acid number, and a basic soap solution a negative acid number. 

Naphthenic acid is a collective name for organic acids present in some but not all crude oils. In addition to true naphthenic acids (naphthenic carboxylic acids represented by the formula X-COOH in which X is a cycloparaffin radical), the total acidity of a crude may include various amounts of other organic acids and sometimes mineral acids. Thus the total neutralization number of a stock, which is a measure of its total acidity, includes (but does not necessaiily represent) the level of naphthenic acids present. The neutralization number is the number of milligrams of potassium hydroxide required to neutralize one gram of stock as determined by titration using phenolphthalein as an indicator, or as determined by potentiometric titration. It may be as high as 10 mg KOH/gr. for some crudes. The neutralization number does not usually become important as a corrosion factor, however, unless it is at least 0.5 mg KOH/gm. 

Brdnsted-Lowry theory, 194 contrast definitions, 194 indicators, 190 reactions, 188 titrations, 188 Acids, 183 aqueous, 179 carboxylic, 334 derivatives of organic, 337 equilibrium calculations, 192 experimental introduction, 183 names of common, 183 naming of organic, 339 properties of, 183 relative strengths, 192, 451 strength of, 190 summary, 185 weak, 190, 193 Actinides, 414 Actinium... 

Non-aqueous titrations have been used to quantify mixtures of primary, secondary and tertiary amines,5 for studying sulphonamides, mixtures of purines and for many other organic amino compounds and salts of organic acids. 

Discussion. Many of the common carboxylic acids are readily soluble in water and can be titrated with sodium hydroxide or potassium hydroxide solutions. For sparingly soluble organic acids the necessary solution can be achieved by using a mixture of ethanol and water as solvent. 

The theory of titrations between weak acids and strong bases is dealt with in Section 10.13, and is usually applicable to both monoprotic and polyprotic acids (Section 10.16). But for determinations carried out in aqueous solutions it is not normally possible to differentiate easily between the end points for the individual carboxylic acid groups in diprotic acids, such as succinic acid, as the dissociation constants are too close together. In these cases the end points for titrations with sodium hydroxide correspond to neutralisation of all the acidic groups. As some organic acids can be obtained in very high states of purity, sufficiently sharp end points can be obtained to justify their use as standards, e.g. benzoic acid and succinic acid (Section 10.28). The titration procedure described in this section can be used to determine the relative molecular mass (R.M.M.) of a pure carboxylic acid (if the number of acidic groups is known) or the purity of an acid of known R.M.M. 

Procedure. Weigh out accurately about 4 g of the pure organic acid, dissolve it in the minimum volume of water (Note 1), or 1 1 (v/v)ethanol/water mixture, and transfer the solution to a 250 mL graduated flask. Ensure the solution is homogeneous and make up to the required volume. Use a pipette to measure out accurately a 25 mL aliquot and transfer to a 250 mL conical flask. Using two drops of phenolphthalein solution as indicator, titrate with standard 0.2M (approx.) sodium hydroxide solution (Note 2) until the colourless solution becomes faintly pink. Repeat with further 25 mL volumes of the acid solution until two results in agreement are obtained. 

Fruit and vegetable juices packed with 21-26 in. of vacuum and stored in uncoated aluminum cans caused severe corrosion as shown in Table III. The corrosion rate brought about by the juices depends more on the nature of the organic acid present and the buffering capacity of the juice than on the total titratable acidity (11). The use of coated aluminum containers considerably minimized corrosion problems. Product control under extended storage conditions may be achieved by using specific chemical additives. However, more work is needed in this area before final conclusions can be reached. 

An acid-base titration can be performed without measuring the pH of the solution, if an indicator is present that changes color as the titration passes the stoi-chiometric point. An indicator is a weak organic acid that contains a highly delocalized 7t bonding network. We use p to designate the p of an indicator. At pH < p, ... 

The evaluation of the total organic acidity was performed by neutralizing (to pH 10-11) a sample of product with NaOH and then retro-titrating with HCl. 

Johansson, P.-A. Gustavii, K., Potentiometric titration of ionizable compounds in two phase systems. 2. Determination of partition coefficients of organic acids and bases, Acta Pharm. Suecica 13, 407 -20 (1976). 

Spectroscopic techniques may provide the least ambiguous methods for verification of actual sorption mechanisms. Zeltner et al. (Chapter 8) have applied FTIR (Fourier Transform Infrared) spectroscopy and microcalorimetric titrations in a study of the adsorption of salicylic acid by goethite these techniques provide new information on the structure of organic acid complexes formed at the goethite-water interface. Ambe et al. (Chapter 19) present the results of an emission Mossbauer spectroscopic study of sorbed Co(II) and Sb(V). Although Mossbauer spectroscopy can only be used for a few chemical elements, the technique provides detailed information about the molecular bonding of sorbed species and may be used to differentiate between adsorption and surface precipitation. 

Potassium iodate is a fairly strong oxidizing agent that may be used in the assay of a number of pharmaceutical substances, for instance benzalkonium chloride, cetrimide, hydralazine hydrochloride, potassium iodide, phenylhydrazine hydrochloride, semicarbazide hydrochloride and the like. Under appropriate experimental parameters the iodate reacts quantitatively with both iodides and iodine. It is, however, interesting to observe here that the iodate titrations may be carried out effectively in the presence of saturated organic acids, alcohol and a host of other organic substances. 

On heating at temperatures above 100°C, lactose is degraded to acids with a concomitant increase in titratable acidity (Figures 9.5, 9.6). Formic acid is the principal acid formed lactic acid represents only about 5% of the acids formed. Acid production is significant in the heat stability of milk, e.g. when assayed at 130°C, the pH falls to about 5.8 at the point of coagulation (after about 20 min) (Figure 9.7). About half of this decrease is due to the formation of organic acids from lactose the remainder is due to the precipitation of calcium phosphate and dephosphorylation of casein, as discussed in section 9.4. 

Sulfamic acid is a stable, non-hygroscopic, monoprotic acid which is very convenient to use as a primary standard in acid-base titrations. The acid hydrolyzes fairly rapidly in boiling water to give ammonium bisulfate. It may be recrystallized from water at 70°C with rapid cooling to avoid decomposition. Sulfamic acid does not dissolve appreciably in oxygenated organic solvents, e.g., alcohols, ethers. 

The taste of foods and beverages often depend on the concentration and type of acid they contain. Two common concepts deal with acidity in foods titratable acidity and pH. Each of these must be determined experimentally as each has its own impact on food quality. Over the years it has been shown that titratable acidity and pH contribute to the acid taste. However, the acid taste of food high in organic acids is dependent primarily on titratable acidity and secondarily on pH (Plane et al., 1980). The following equation has been proposed by Plane et al. to determine an acid taste index, i.e., acidity index (/a), of a food sample ... 

By Titration.—A crystalline salt of the base with some mineral or organic acid is prepared and purified, and the acid present in a weighed... 

Acid-Base. The pH of natural waters is determined primarily by the carbonate equilibria. However, organisms may produce amounts of organic matter or ammonia sufficient to influence the pH and buffer capacity of the waters. It would be of interest to determine titration curves of high organic, high color, low alkalinity waters leached from some marshes. It is possible that these waters contain sufficient amounts of organic acids to be significant. 

The end point in an acid-base titration can be determined either by an acid-base indicator or by means of a potentiometer (or a pH meter). An acid-base indicator is a weak organic acid or a weak organic base which can be written as... 

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