Titration with alkaline solutions method

Ewins s Method o-i-o-2 gm. of the substance is mixed in a 300 ml. Kjeldahl flask with 10 gm. potassium sulphate, o>2-o-3 gm. starch and 20 ml. concentrated sulphuric acid. This mixture is then heated by means of a Bunsen burner, first moderately for 10-15 minutes, then more vigorously for about 4 hours, until decomposition is complete. The liquid is cooled, transferred to a 350 ml. flask and made alkaline to litmus paper with sodium hydroxide. It is then cooled to 30° to 40° and sulphuric acid added drop by drop until the solution is faintly acid. A saturated solution of sodium bicarbonate is then added until the solution is again alkaline, 5-10 ml. being added in excess. The arsenious acid formed is then titrated with iodine solution using starch as indicator. 

Puschel and Stefanac ° use alkaline hydrogen peroxide in the oxygen flask method to oxidize arsenic to arsenate. The arsenate is titrated directly with standard lead nitrate solution with 4-(2-pyridylazo) resorcinol or 8-hydroxy-7-(4-sulpho-l-naphthylazo) quino-line-5-sulphonic acid as indicator. Phosphorus interferes in this method. The precision at the 99% confidence limit is within 0.67% for a 3-mg sample. In another variation, Stefanac used sodium acetate as the absorbing liquid, and arsenite and arsenate are precipitated with silver nitrate. The precipitate is dissolved in potassium nickel cyanide (K2Ni(CN)4) solution and the displaced nickel is titrated with EDTA solution, with murexide as indicator. The average error is within + 0.19% for a 3-mg sample. Halogens and phosphate interfere in the procedure. 

Hydrolysis is a standard procedure for determining carboxamides. Alkaline hydrolysis yields ammonia or an amine which can usually be distilled out and easily detected or determined, e.g. by titration with acid. This method can be applied to sulphonamides, usually under rather more vigorous conditions359,360. Acid hydrolysis is also possible the solution can then be made alkaline and the ammonia or amine distilled and determined as after alkaline hydrolysis361. In another published work, the sulphonic acid product was isolated, e.g. by using an ion exchanger, and titrated with alkali362. 

Alicino l described an iodometric method for the determination of penicillins. Only after alkaline or penicillinase hydrolysis the penicillins consume iodine. The difference in consumption of iodine before and after hydrolysis is proportional to the quantity of the antibiotic. Russo-Alesi used the iodometric titration for estimation of ampicillin in formulations. Ampicillin solutions were hydrolyzed with sodium hydroxide for 30 minutes. After acidification the iodine solution was added. After an additional 30 minutes, the excess of iodine was titrated with thiosulfate solution. A blank consisted of unhydrolyzed ampicillin. The ampicillin standard was treated in exactly the same manner and used in calculations. The hydrolysis of ampicillin with penicillinase instead with sodium hydroxide makes the method more selective. 

In this experiment you will prepare temporarily hard water study some of the chemical properties of soft, temporarily hard, and permanently hard water and study various processes available for softening hard water. The hardness of different water samples will be tested quantitatively by determining the volume of soap solution that must be added to a given volume of water in order to obtain a lather. Moreover, hard water will be treated by several methods designed to soften it, and the treated water will be titrated with soap solution to test the effectiveness of the methods. A study of the hardness of water, the action of soaps, and methods for softening water will illustrate characteristic chemical reactions and important differences in solubilities of some compounds of alkali metals and the alkaline earth metals. In addition, you will become familiar with a laboratory preparation for and properties of carbon dioxide gas. 

For many years fluorine has been deterrnined by the Willard-Winters method in which finely ground ore, after removal of organic matter, is distilled with 72% perchloric acid in glass apparatus. The distillate, a dilute solution of fluorosiUcic acid, is made alkaline to release fluoride ion, adjusted with monochloroacetic acid at pH 3.4, and titrated with thorium nitrate, using sodium a1i2arine sulfonate as indicator. 

Devarda s Method. Nitrogen in nitrates or nitric acid also may be deterrnined by the Kjeldahl method or by Devarda s method. The latter is both convenient and accurate when no organic nitrogen is present. The nitrate is reduced by Devarda s alloy to ammonia in an alkaline solution. The ammonia is distilled and titrated with standard acid. 

A similar procedure may also be used for the determination of antimony(V), whilst antimony (III) may be determined like arsenic(III) by direct titration with standard iodine solution (Section 10.113), but in the antimony titration it is necessary to include some tartaric acid in the solution this acts as complexing agent and prevents precipitation of antimony as hydroxide or as basic salt in alkaline solution. On the whole, however, the most satisfactory method for determining antimony is by titration with potassium bromate (Section 10.133). 

Various workers have discussed the determination of total alkalinity and carbonate [ 10-12], and the carbonate bicarbonate ratio [ 12] in seawater. A typical method utilises an autoanalyser. Total alkalinity (T milliequivelents per litre) is found by adding a known (excess) amount of hydrochloric acid and back titrating with sodium hydroxide solution a pH meter records directly and after differentiation is used to indicate the end-point. Total carbon dioxide (C milliequivelents per litre of HCO3 per litre) is determined by mixing the sample with dilute sulfuric acid and segmenting it with carbon dioxide-free air, so that the carbon dioxide in the sample is expelled into the air segments. The air... 

Soliman and Belal investigated argentimetric (67,68) and mercurimetric (69) methods. Hydralazine precipitates silver from ammoniacal silver nitrate solution. The silver is dissolved with hot nitric acid and titrated with ammonium thiocyanate solution. Alternatively, mercury is precipitated from alkaline potassium mercuric iodide solution. The precipitated mercury is dissolved by adding excess standard iodine solution. The excess iodine is back-titrated with sodium thiosulfate solution after acidifying with acetic acid. 

Singhal et al. [78, 79] have described a titrimetric method for the determination of low levels of Oxamyl residues in soils. Their investigations revealed that after hydrolysis Oxamyl gave a brown precipitate with carbon disulphide and an alkaline solution of copper(II) sulphate. This reaction suggested a procedure for the determination of Oxamyl by titration with ethylene diamine tetracetic acid of the copper remaining unreacted to the 1-(2 pyridylazo)-2-naphthol end-point indicator). The following stoichiometric reaction appeared to occur between Oxamyl and the reagents ... 

The complexometric method for determination of Ca(II) and Mg(II) is based on two titrations with EDTA in alkaline solution, one where both ions are determined together and the second after one of them has been masked with a specific complexing agent. The effect of interfering heavy metals such as Cu, Fe, Mn or Zn can be avoided by adding cyanide. The AOAC Official Method 964.01 for determination of acid-soluble... 

Mg in fertilizers is based on such proceedings thereof has been applied on multiple occasions. In milk fermentation, where the samples were dried, calcined in a furnace at 600 °C, the ash was dissolved in 0.03 M HCl, the solution was centrifuged and the supernatant was thus analyzed . The complexometric method for determination of Ca(II) and Mg(II) can be carried out in a single titration with EDTA in alkaline solution, using a Ca-ISE for potentiometric determination of two endpoints. This is accomplished on digitally plotting pCa values measured by the ISE as a function of the volume V of titrant added to the aliquot of analyte the first and second inflection points of the curve mark the Ca(II) and Mg(n) equivalences, respectively. ... 

An accurate electrometric method applicable to soluble sulphides consists in precipitating as silver sulphide in alkaline solution by titration with standard ammoniacal silver solution.6 The change of E.M.F. at the end-point is considerable. The method is satisfactory in the presence of sulphite, sulphate, thiosulphate, polysulphide or chloride. 

Some of the volumetric methods described above may also be adapted to the electrometric determination of arsenic. Such methods have been described for titration of arsenites with ceric sulphate,9 iodine in the presence of sodium bicarbonate,10 chloramine (p-toluene-sulphone chloramide),11 alkaline potassium ferricyanide solution,12 potassium bromate13 or potassium iodate14 in the presence of hydrochloric acid, silver nitrate15 (by applying a secondary titration with 01N alkali to maintain the desired low H+-ion concentration), and with... 

Other important tests are for acid and alkalinity number and for water content (266), because water content and alkalinity of the polyether glycol can influence the reaction with isocyanates. The standard ASTM test for acid and alkalinity number, ASTM D4662 (267), is not sensitive enough for the low acidity and alkalinity numbers of PTMEG, and special methods have been developed. A useful alkalinity number (AN) has been defined as milliequivalents KOH per 30 kg of PTMEG, as titrated in methanol solution with 0.005 N HC1 (268). Other useful nonstandard tests are for heavy metals, sulfated ash, and peroxide. The peroxides formed initially in oxidations are quickly transformed into carbonyl groups, which are detectable by infrared spectroscopy. On oxidation, a small C—O peak develops at 1726 cm-1 and can be detected in thick (0.5-mm) films. A relative ratio of this peak against an internal standard peak at 2075 C—O is sometimes defined as the carbonyl ratio. 

The first of these, utilized by Yoder, McCalip and Seibert,34 and by Balch, Broeg and Ambler,37 provides for the extraction of the aconitic acid from the sample being investigated, usually with diethyl ether, and the subsequent isolation of the acid from the solvent. In dealing with solid samples, e.g. alkaline earth aconitates, evaporator scale, etc., the prescribed procedure is to dissolve the material in aqueous mineral acid and to extract the acid solution exhaustively with ether. The ether extract is then evaporated under reduced pressure, the dried residue titrated with standard alkali and the titratable acid calculated as aconitic acid. In dealing with such solid samples it is often necessary to make an additional determination for oxalic acid which otherwise would be assumed to be aconitic acid.37 The aconitic acid in liquid samples is usually precipitated as the insoluble lead salt which is separated and treated as any other solid sample. In some cases this procedure is unnecessary and the liquid samples are merely acidified with a mineral acid and then extracted with ether.37 This method for the determination of aconitic acid, however, requires a considerable amount of time and is further complicated by the interference of ether-soluble waxes and non-volatile acids. 

Estimation of Atmospheric Carbon Dioxide.—A convenient method is that of Pettenkofer,4 which consists in introducing a standard solution of barium hydroxide into a large bottle containing several litres of the air to be examined. The bottle is shaken from time to time to keep the sides moistened wit-h the solution, and after 5 or 6 hours the absorption of carbon dioxide may be regarded as complete. The baryta solution is decanted into a small stoppered bottle and allowed to stand until any suspended barium carbonate has settled. A portion of the clear liquid is then removed and titrated with dilute sulphuric acid, using phenol-phthalein as indicator. The diminution in alkalinity due to combination with carbonic acid is thus measured, and from the data obtained the percentage of carbon dioxide m the atmosphere may easily be calculated. 

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