Sodium hydroxide standardization

Sodium Hydroxide, Standard Solutions (0.03 M)— Prepare by mixing 7 parts of water with 3 parts of standtud 0.1 A/sodium hydroxide (NaOH) solution. Concentrate 400 mL of 0.03 Af NaOH solution by evaporating to 30 mL, and determine any sulfate present in accordance with Appendix Al, Turbidimetric Procedure for Sulfate of Test Method D 1266. If sulfate is found, corrections must be made for any sulfur introduced by the reagent in the alkali titration following combustion. 

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 . 

Standards for dmg chemicals are pubUshed ia USP—NE. Dmg substances are chemicals that have therapeutic or diagnostic uses, whereas pharmaceutical iagredients provide preservative action, fiavoiing, or hilfillment of a function ia the formulation of dosage-form dmgs. Examples of dmg substances are acetaminophen [103-90-2] ampicillin [69-53-4] aspirin [50-78-2] powdered ipecac, riboflavin [83-88-5] staimous fluoride [7783-47-3] and thyroid. Examples of pharmaceutical iagredients are ethylparaben [120-47-8] lactose [63-42-3] magnesium stearate [557-04-0] sodium hydroxide [1310-73-2] starch [9005-25-8] and vanillin [121-33-5],... 

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 reactor effluent, containing 1—2% hydrazine, ammonia, sodium chloride, and water, is preheated and sent to the ammonia recovery system, which consists of two columns. In the first column, ammonia goes overhead under pressure and recycles to the anhydrous ammonia storage tank. In the second column, some water and final traces of ammonia are removed overhead. The bottoms from this column, consisting of water, sodium chloride, and hydrazine, are sent to an evaporating crystallizer where sodium chloride (and the slight excess of sodium hydroxide) is removed from the system as a soHd. Vapors from the crystallizer flow to the hydrate column where water is removed overhead. The bottom stream from this column is close to the hydrazine—water azeotrope composition. Standard materials of constmction may be used for handling chlorine, caustic, and sodium hypochlorite. For all surfaces in contact with hydrazine, however, the preferred material of constmction is 304 L stainless steel. 

Oxidation. The oxidation reactions of organoboranes have been reviewed (5,7,215). Hydroboration—oxidation is an anti-Markovnikov cis-hydration of carbon—carbon multiple bonds. The standard oxidation procedure employs 30% hydrogen peroxide and 3 M sodium hydroxide. The reaction proceeds with retention of configuration (216). 

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. 

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. 

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). 

Occupational Safety and Health. OSHA has set no specific limits for sodium and potassium sibcates (88). A pmdent industrial exposure standard could range from the permissible exposure limit (PEL) for inert or nuisance particulates to the PEL for sodium hydroxide, depending on the rate of dissolution and the concentration of airborne material. Material safety data sheets issued by siUcate producers should be consulted for specific handling precautions, recommended personal protective equipment, and other important safety information. 

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). 

The side-chain chlorine contents of benzyl chloride, benzal chloride, and benzotrichlorides are determined by hydrolysis with methanolic sodium hydroxide followed by titration with silver nitrate. Total chlorine determination, including ring chlorine, is made by standard combustion methods (55). Several procedures for the gas chromatographic analysis of chlorotoluene mixtures have been described (56,57). Proton and nuclear magnetic resonance shifts, characteristic iafrared absorption bands, and principal mass spectral peaks have been summarized including sources of reference spectra (58). Procedures for measuring trace benzyl chloride ia air (59) and ia water (60) have been described. 

Wet-Chemical Determinations. Both water-soluble and prepared insoluble samples must be treated to ensure that all the chromium is present as Cr(VI). For water-soluble Cr(III) compounds, the oxidation is easily accompHshed using dilute sodium hydroxide, dilute hydrogen peroxide, and heat. Any excess peroxide can be destroyed by adding a catalyst and boiling the alkaline solution for a short time (101). Appropriate ahquot portions of the samples are acidified and chromium is found by titration either using a standard ferrous solution or a standard thiosulfate solution after addition of potassium iodide to generate an iodine equivalent. The ferrous endpoint is found either potentiometricaHy or by visual indicators, such as ferroin, a complex of iron(II) and o-phenanthroline, and the thiosulfate endpoint is ascertained using starch as an indicator. 

The sodium carbonate content may be deterrnined on the same sample after a slight excess of silver nitrate has been added. An excess of barium chloride solution is added and, after the barium carbonate has setded, it is filtered, washed, and decomposed by boiling with an excess of standard hydrochloric acid. The excess of acid is then titrated with standard sodium hydroxide solution, using methyl red as indicator, and the sodium carbonate content is calculated. 

The preparation of cyclohexylmagnesium bromide is described on p. 22. The solution may be standardized by titrating against 0.5 N hydrochloric acid, and exactly one mole equivalent is used in the preparation. Five cubic centimeters of cyclohexylmagnesium bromide solution is slowly added to 20 cc. of water, an excess of the standard acid is added, and the excess acid titrated with sodium hydroxide. If 85 g. (3.5 moles) of magnesium, one liter of dry ether, and 571 g. of cyclohexyl bromide (3.5 moles) are used, a solution results which is about 2 molar. 

FIGURE 7.15 Long-term stability of Fractogel EMD BioSEC (S) after long-term treatment with sodium hydroxide. The chromatography of standard proteins (for conditions, see Fig. 7.2A) was carried out after various times of exposure to I M sodium hydroxide solution and reequilibration of the column with the buffer. 

An alcohol-free solution of diazomethane in ether is prepared as in Chapter 17, Section III. This solution is approximately 0.5 M in diazomethane and may be standardized by titration as follows benzoic acid (0.6 g, approx. 0.005 mole) is weighed accurately into an Erlenmeyer flask and suspended in 5 ml of ether. The diazomethane solution (approx. 5 ml) is added from a buret with swirling, care being taken that an excess of unreacted benzoic acid remains (the yellow color of the diazomethane should be completely discharged). The excess benzoic acid is now titrated with standard 0.2 N sodium hydroxide solution, and the concentration of diazomethane is calculated. 

A second major use of sulfuric acid of commerce is in reactions with bases. In laboratory use it is diluted to a much lower concentration and can be used as a standard acid. A typical problem would be the titration of a base solution of unknown concentration using a sulfuric acid solution of known concentration. For example, What is the concentration of a sodium hydroxide solution if 25.43 ml of the NaOH solution just reacts with 18.51 ml of 0.1250 M HiSOt (to produce a neutral solution) ... 

Standard retrosynthetic manipulation of PGA2 (1) converts it to 5 (see Scheme 2). A conspicuous feature of the five-membered ring of intermediate 5 is the /(-keto ester moiety. Retrosynthetic cleavage of the indicated bond in 5 furnishes triester 6 as a potential precursor. Under basic conditions and in the synthetic direction, a Dieck-mann condensation4 could accomplish the formation of a bond between carbon atoms 9 and 10 in 6 to give intermediate 5. The action of sodium hydroxide on intermediate 5 could then accomplish saponification of both methyl esters, decarboxylation, and epi-merization adjacent to the ketone carbonyl to establish the necessary, and thermodynamically most stable, trans relationship between the two unsaturated side-chain appendages. 

The biogenetic scheme for endiandric acids also predicts the plausible existence in nature of endiandric acids E (5), F (6), and G (7). Even though they are still undiscovered, their synthesis has been achieved (Scheme 6). For endiandric acids E and F, key intermediate 24 is converted, by conventional means, to aldehyde 35 via intermediate 34. Oxidation of 35 with silver oxide in the presence of sodium hydroxide results in the formation of endiandric acid E (5) in 90 % yield, whereas elaboration of the exo side chain by standard olefination (85 % yield) and alkaline hydrolysis (90 % yield) furnishes endiandric acid F (6). The construction of the remaining compound, endiandric acid G (7), commences with the methyl ester of endiandric acid D (36) and proceeds by partial reduction to the corresponding aldehyde, followed by olefination and hydrolysis with aqueous base as shown in Scheme 6. 

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