Sodium hydroxide standard solution

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. 

A sample of oxalic acid, H2C204, is titrated with standard sodium hydroxide, NaOH, solution. A total of 45-20 mL of 0.1200 M NaOH is required to completely neutralize 20.00 mL of the acid. What is the concentration of the acid ... 

Sodium hydroxide stock solutions were prepared of three different concentrations, viz., 0.1, 1.0 and 10M. The 0.1 and 1.0M solutions were obtained by diluting Baker reagent grade Dilut-it standardized solutions. The 10M solution was prepared by dilution of 50% Baker Analyzed sodium hydroxide (18.86M). Carbonate free water was used for all dilutions and the solutions were protected from contact with air. 

Rezk et al. [74] developed and validated a reversed-phase HPLC assay method for the simultaneous quantitative determination of omeprazole and its three metabolites in human plasma. The method provides excellent chromatographic resolution and peak shape for the four components and the internal standard within a 17-min run time. The simple extraction method results in a clean baseline and relatively high extraction efficiency. The method was validated over the range of 2-2000 ng/ml. The resolution and analysis for the four analytes omeprazole, hydroxyome-prazole, omeprazole sulfone, and omeprazole sulfide and the internal standard utilized a Zorbax C18 (15 cm x 3 mm, 5 /im) with a Zorbax C18 (12.5 cm x 4.6 mm) guard column. The mobile phase consisted of two components. Mobile phase A was 22 mM phosphate monobasic, adjusted to a pH of 6 with diluted sodium hydroxide. This solution was filtered through a 0.45-/im membrane filter, then mixed as 900 ml buffer to 100 ml methanol. Mobile phase B was composed of 100 ml of the phosphate buffer as mobile phase A, mixed with 800 ml of acetonitrile, 100 ml of methanol, and 100 /A of trifluoroacetic acid with an initial flow-rate of 0.55 ml/min and detection at 302 nm. 

Standardized Sodium Thiosulfate Solution Dissolve about 8.7 g of sodium thiosulfate (Na2S203-5H20) and 67 mg of sodium carbonate in 1000 mL of freshly boiled and cooled water. Add 3 mL of 1.0 N sodium hydroxide. This solution contains 5.54 g of sodium thiosulfate. Standardize to 0.0333 N as directed for 0.1 N Sodium Thiosulfate (see Volumetric Solutions under Solutions and Indicators). Adjust the normality repeatedly, if necessary. 

The only experiment, which leads to a determination of the standard enthalpy of formation of sodium selenite, appears to be that of Thomsen [1882THO]. He measured the enthalpy of the reaction between one mole of selenious acid and two moles of sodium hydroxide in solution. The data are used to calculate the standard enthalpy of formation ofNaSeOsCcr) in Table A-1. 

Obtain in a clean, dry beaker about 50. mL of approximately 0.1 M sodium hydroxide, NaOH, solution from the reagent bench. Record the exact concentration of the base in TABLE 16.1C. Rinse your buret with about 10. mL of the standard base. Then add a few milliliters of the standard base to the buret, fill the buret tip completely by manipulating the stopcock or pinch clamp, check to be certain that there are no air bubbles in the buret tip, and add the rest of your standard base to the buret. 

The analysis of the copper-ammine complex for the ammonia, NH3, content will involve an acid-base "back titration." In this analysis, you will react the complex with an accurately measured volume of standardized hydrochloric acid, HCl, solution. The volume of HCl solution should be sufficient to react with all the ammonia and leave some excess HCl. The excess HCl will then be back reacted with standardized sodium hydroxide, NaOH, solution. The difference between the number of moles of HCl added and the number of moles of excess HCl will give the number of moles of ammonia in your measured quantity of copper-ammine complex. For your information, you cannot titrate the ammonia directly with HCl because of problems with seeing the color changes of the appropriate indicator in the presence of the colored copper-ammine complex. 

A solution of the strong base sodium hydroxide can be used as the standard solution in a titration, but it must first be standardized, because sodium hydroxide in solution reacts with carbon dioxide in the air, making its concentration unstable over time. We can standardize the sodium hydroxide solution by titrating it against an acid solution of accurately known concentration. The acid often chosen for this task is a monoprotic acid called potassium hydrogen phthalate (KHP), for which the molecular formula is KHCgH404. KHP is a white, soluble solid that is commercially available in highly pure form. The reaction between KHP and sodium hydroxide is... 

Extraction. Aliquots of the samples were transferred into test tubes containing small amounts of internal standard, then homogenized with 0.5 M sodium hydroxide / ethyl acetate (1/1), and centrifuged. The ethyl acetate layer was transferred to a new tube and back-extracted with 1 M hydrochloric acid. After aspiration of the ethyl acetate layer, the hydrochloric acid was alkalinized by the addition of 5 M sodium hydroxide. The solution was extracted with ethyl acetate. The ethyl acetate layer was transferred to a new tube, and then evaporated to dryness under a flow of nitrogen gas. The resultant residue was reconstituted in the mobile phase for injection into the HPLC. The lowest measurable concentration was 0.1 xg/ml (or p,g/g wet tissue). 

Alkaline Standard. Take 10 ml of the B.P. boric acid-potassium chloride-sodium hydroxide buffer solution at pH 8 7 and add 1 drop of 0 1 per cent solution of neutral red in 50 per cent ethanol and 3 drops of 01 per cent solution of phenolphthalein in 50 per cent ethanol. 

A calibration graph is plotted using aliquots of the boron standard solution (H), containing 0.25 to 3 pg of boron. These aliquots are transferred into platinum dishes containing 3 ml sodium hydroxide-glycerol solution (D). After evaporation to dryness on a boiling water bath, the procedure is continued as described above. A solution without boron addition is used as blank. 

The liberated iodine is titrated with standard sodium thiosulphate(Vr) solution after acidification to remove the hydroxide ions. 

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 . 

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. 

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. 

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). 

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). 

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) ... 

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