Sodium hydroxide titration

Weak acid with a strong base. In the titration of a weak acid with a strong base, the shape of the curve will depend upon the concentration and the dissociation constant Ka of the acid. Thus in the neutralisation of acetic acid (Ka— 1.8 x 10-5) with sodium hydroxide solution, the salt (sodium acetate) which is formed during the first part of the titration tends to repress the ionisation of the acetic acid still present so that its conductance decreases. The rising salt concentration will, however, tend to produce an increase in conductance. In consequence of these opposing influences the titration curves may have minima, the position of which will depend upon the concentration and upon the strength of the weak acid. As the titration proceeds, a somewhat indefinite break will occur at the end point, and the graph will become linear after all the acid has been neutralised. Some curves for acetic acid-sodium hydroxide titrations are shown in Fig. 13.2(h) clearly it is not possible to fix an accurate end point. 

Free Fatty Acids in Crude and Refined Fats and Oils (FFA) (Ca 5a-40) determines FFA, as oleic acid, by ethanolic sodium hydroxide titration. 

Dissolve 1 g of sample, accurately weighed, in 50% ethanol/ water that previously has been neutralized to phenolphthalein TS with 0.1 A sodium hydroxide. Titrate with 0.5 N sodium hydroxide to a pink color. Each milliliter of titrant is equivalent to the amount of substance specified below. 

Make several reagent blank determinations, using only the chromium trioxide solution in the above procedure. The ratio of the sodium hydroxide titration (Vb) to the sodium thiosulfate titration (7b), corrected for variation in normalities, will give the acidity-to-oxidizing ratio, V b/Kb = K, for the chromium trioxide carried over in the distillation. The factor K should be constant for all determinations. 

Calculation From the Standard Test Dilution, plot the volume of 0.1 A sodium hydroxide titrated against time. Using only the points that fall on the straight-line segment of the curve, calculate the mean acidity released per min by the Assay Test Dilution. Taking into consideration dilution factors, calculate the lipase activity of the Standard Test Dilution, using the lipase activity of the USP Pancreatin Reference Standard stated on the label. 

To check the mass balance of the reaction, the reaction products were analyzed after each run by a thorium nitrate method for fluoride and by a sodium hydroxide titration for hydrogen ions. 

Lisinoprii can be determined by potentiometric titration with aqueous sodium hydroxide and non-aqueous perchioric acid. The sodium hydroxide titration is carried out by titrating the iisinoprii potentiometrically with carbonate free 0.1 N NaOH to one endpoint using a combination eiectrode. Lisinoprii can aiso be determined by titration potentiometricaiiy with 0.1 N perchloric acid in acetic acid to one endpoint. The electrode system consists of a glass electrode (such as a Metrohm Model EA 107 vs. a silver/silver chloride reference electrode such as a Metrohm Model EA 432 filled with 0.1 N lithium perchlorate in glacial acetic acid. 

E. Assay of Commercial Aspirin by Sodium Hydroxide Titration... 

Add by pipette 25 ml 0.5 M sodium hydroxide. Titrate to phenolphtha-lein with the same solution. 

Dibasic acids such as fumaric and succinic would be included in the determination of the acid. If other acids are present, the sodium hydroxide titration would probably indicate their presence and would also serve as a check for the anhydride content. 

To 10 ml of an approximately 5 per cent solution of phenazone add 90 ml of approximately 0 05N picric acid. Shake the mixture, leave overnight, filter and titrate 50 ml of the filtrate with 0-1N sodium hydroxide. Titrate 90 ml of the original picric acid solution with 0-1N sodium hydroxide, then subtract twice the former titration from this... 

Dissolve 0-3 g in about 75 ml of water in a separator and add 0-4 ml of bromophenol blue test solution (0-1 g of bromophenol blue dissolved in 3 ml of 0 05N sodium hydroxide and diluted to 200 ml with water), 10 ml of chloroform and 1 ml of N sodium hydroxide. Titrate with 0-02M sodium tetraphenylboron to the disappearance of the blue colour from the chloroform layer, adding the titrant dropwise towards the end of the titration and shaking vigorously after each addition. 1 ml 0 02M = 0-008962 g C27H42O2NCI. 

When a saturated solution of sulphur dioxide is titrated against approximately 2 M sodium hydroxide solution the following pH curve is obtained Figure 10.4) ... 

Larger fragments of porcelain would absorb appreciable quantities of the sodium hydroxide, which would be only slowiy extracted by the acid during the subsequent titration hence finely dh ided carborundum may well be used (P. 8). 

Transfer 25 ml. of this dilute solution by means of a pipette to a conical flask, and add similarly 50 ml. of Ml 10 iodine solution. Now-add 10% sodium hydroxide solution until the liquid becomes pale yeilow in colour, and allow the solution to stand, with occasional shaking, at room temperature for at least 10 minutes. Then acidify with dilute hydrochloric acid (free from chlorine) in order to liberate the remaining iodine. Titrate the latter w ith Mho sodium thiosulphate solution, using starch as an indicator in the usual way. 

Weigh out accurately about 2 g. of glycine, transfer to a 250 ml. graduated flask, dissolve in distilled water, make up to the mark, and mix well. Transfer 25 ml. of the solution to a conical flask, add 2 drops of phenolphthalein, and then again add dilute sodium hydroxide very carefully until the solution is just faintly pink. No v add about 10 ml. (/. ., an excess) of the neutralised formaldehyde solution the pink colour of the phenolphthalein disappears immediately and the solution becomes markedly acid. Titrate with AI io sodium hydroxide solution until the pink colour is just restored. Repeat the process with at least two further quantities of 25 ml. of the glycine solution in order to obtain consistent readings. 

The most common strong base for titrating acidic analytes in aqueous solutions is NaOH. Sodium hydroxide is available both as a solid and as an approximately 50% w/v solution. Solutions of NaOH may be standardized against any of the primary weak acid standards listed in Table 9.7. The standardization of NaOH, however, is complicated by potential contamination from the following reaction between CO2 and OH . 

The most popular device for fluoride analysis is the ion-selective electrode (see Electro analytical techniques). Analysis usiag the electrode is rapid and this is especially useful for dilute solutions and water analysis. Because the electrode responds only to free fluoride ion, care must be taken to convert complexed fluoride ions to free fluoride to obtain the total fluoride value (8). The fluoride electrode also can be used as an end poiat detector ia titration of fluoride usiag lanthanum nitrate [10099-59-9]. Often volumetric analysis by titration with thorium nitrate [13823-29-5] or lanthanum nitrate is the method of choice. The fluoride is preferably steam distilled from perchloric or sulfuric acid to prevent iaterference (9,10). Fusion with a sodium carbonate—sodium hydroxide mixture or sodium maybe required if the samples are covalent or iasoluble. 

Procedures for determining the quaUty of formaldehyde solutions ate outlined by ASTM (120). Analytical methods relevant to Table 5 foUow formaldehyde by the sodium sulfite method (D2194) methanol by specific gravity (D2380) acidity as formic acid by titration with sodium hydroxide (D2379) iron by colorimetry (D2087) and color (APHA) by comparison to platinum—cobalt color standards (D1209). 

The concentration of aqueous solutions of the acid can be deterrnined by titration with sodium hydroxide, and the concentration of formate ion by oxidation with permanganate and back titration. Volatile impurities can be estimated by gas—Hquid chromatography. Standard analytical methods are detailed in References 37 and 38. 

The fermentation-derived food-grade product is sold in 50, 80, and 88% concentrations the other grades are available in 50 and 88% concentrations. The food-grade product meets the Vood Chemicals Codex III and the pharmaceutical grade meets the FCC and the United States Pharmacopoeia XK specifications (7). Other lactic acid derivatives such as salts and esters are also available in weU-estabhshed product specifications. Standard analytical methods such as titration and Hquid chromatography can be used to determine lactic acid, and other gravimetric and specific tests are used to detect impurities for the product specifications. A standard titration method neutralizes the acid with sodium hydroxide and then back-titrates the acid. An older standard quantitative method for determination of lactic acid was based on oxidation by potassium permanganate to acetaldehyde, which is absorbed in sodium bisulfite and titrated iodometricaHy. 

Aqueous titration with IN sodium hydroxide is the usual malic acid assay. Maleic and fumaric acid are deterrnined by a polarographic method. Analytical methods have been described (40). 

Functional Group Analysis. The total hydroxyl content of lignin is determined by acetylation with an acetic anhydride—pyridine reagent followed by saponification of the acetate, and followed by titration of the resulting acetic acid with a standard 0.05 W sodium hydroxide solution. Either the Kuhn-Roth (35) or the modified Bethge-Liadstrom (36) procedure may be used to determine the total hydroxyl content. The aUphatic hydroxyl content is determined by the difference between the total and phenoHc hydroxyl contents. 

Analytical and Test Methods. Potentiometric titration with sodium hydroxide [1310-73-2] is employed. Both equivalent points are... 

The titration curve of phosphoric acid in the presence of sodium hydroxide is shown in Figure 1. Three steps, corresponding to consecutive replacement of the three acidic hydrogens, and two inflection points, near pH = 4.5 and 9.0, are evident. Dissociation constants are = 7.1 x 10 = 6.3 x 10 ... 

Fig. 1. Titration curve of orthophosphoric acid in the presence of sodium hydroxide.

Commercial Hquid sodium alumiaates are normally analyzed for total alumiaa and for sodium oxide by titration with ethylene diaminetetraacetic acid [60-00-4] (EDTA) or hydrochloric acid. Further analysis iacludes the determiaation of soluble alumiaa, soluble siHca, total iasoluble material, sodium oxide content, and carbon dioxide. Aluminum and sodium can also be determiaed by emission spectroscopy. The total iasoluble material is determiaed by weighing the ignited residue after extraction of the soluble material with sodium hydroxide. The sodium oxide content is determiaed ia a flame photometer by comparison to proper standards. Carbon dioxide is usually determiaed by the amount evolved, as ia the Underwood method. 

A number of simple, standard methods have been developed for the analysis of ammonium compounds, several of which have been adapted to automated or instmmental methods. Ammonium content is most easily deterrnined by adding excess sodium hydroxide to a solution of the salt. Liberated ammonia is then distilled into standard sulfuric acid and the excess acid titrated. Other methods include colorimetry (2) and the use of a specific ion electrode (3). 

The sodium hydroxide is titrated with HCl. In a thermometric titration (92), the sibcate solution is treated first with hydrochloric acid to measure Na20 and then with hydrofluoric acid to determine precipitated Si02. Lower sibca concentrations are measured with the sibcomolybdate colorimetric method or instmmental techniques. X-ray fluorescence, atomic absorption and plasma emission spectroscopies, ion-selective electrodes, and ion chromatography are utilized to detect principal components as weU as trace cationic and anionic impurities. Eourier transform infrared, ft-nmr, laser Raman, and x-ray... 

For crystal sulfamic acid assay, a simplified procedure of neutralization titration with sodium hydroxide solution may be used. At the end point, Bromothymol Blue (BTB) indicator changes color from yellow to yellowish green. A 1-mL solution of l/2NNaOH is equivalent to 0.0485 g of sulfamic acid. 

Analytical Methods. A classical and stiU widely employed analytical method is iodimetric titration. This is suitable for determination of sodium sulfite, for example, in boiler water. Standard potassium iodate—potassium iodide solution is commonly used as the titrant with a starch or starch-substitute indicator. Sodium bisulfite occurring as an impurity in sodium sulfite can be determined by addition of hydrogen peroxide to oxidize the bisulfite to bisulfate, followed by titration with standard sodium hydroxide (279). 

Assay of beryUium metal and beryUium compounds is usuaUy accompHshed by titration. The sample is dissolved in sulfuric acid. Solution pH is adjusted to 8.5 using sodium hydroxide. The beryUium hydroxide precipitate is redissolved by addition of excess sodium fluoride. Liberated hydroxide is titrated with sulfuric acid. The beryUium content of the sample is calculated from the titration volume. Standards containing known beryUium concentrations must be analyzed along with the samples, as complexation of beryUium by fluoride is not quantitative. Titration rate and hold times ate critical therefore use of an automatic titrator is recommended. Other fluotide-complexing elements such as aluminum, sUicon, zirconium, hafnium, uranium, thorium, and rate earth elements must be absent, or must be corrected for if present in smaU amounts. Copper-beryUium and nickel—beryUium aUoys can be analyzed by titration if the beryUium is first separated from copper, nickel, and cobalt by ammonium hydroxide precipitation (15,16). 

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