Titration with alkaline solutions

Distinguishing these acidic oxides is possible by multibasic titration (Boehm et al., 1964), titration with alkaline solutions of different... 

The alkaline solution of thymol is made up to 100 or 200 c.c. as the case may require, using a 5 per cent, soda solution. To 10 c.c. of this solution in a graduated 500 c.c. flask is added a normal iodine solution in shgbt excess, whereupon the thymol is precipitated as a dark reddish-brown iodine compound. In order to ascertain whether a sufficient quantity of iodine has been added, a few drops are transferred into a test tube and a few drops of dilute hydrochloric acid are added. When enou iodine is present, the brown colour of the solution indicates the presence of io ne, otherwise the liquid appears milky by the separation of thymol. If an excess of iodine is present, the solution is slightly acidified with dilute hydrochloric acid and diluted to 500 c.c. From this 100 c.c. are filtered,off, and the excess of iodine determined by titration with normal solution of sodium thiosulphate. For calculation, the number of cubic centimetres required is deducted from the number of cubic centimetres of normal iodine solution added and the resultant figure multiplied by 5, which gives the number of cubia centimetres of iodine required by the thymol. 

For analysis by titration with Fehling s solution, the sample is treated with lead acetate to precipitate protein and fat, filtered, and the filtrate titrated with alkaline CuS04, while heating. The reactions involved are summarized in Figure 2.37. 

Some waters may naturally be acid due to lean nature (almost no dissolved alkaline solids) and presence of biological breakdown products (humic and fulvic acids, etc.) or free CO2. Measured by titration with caustic solution to pH 4.2 (methyl orange). 

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. 

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. 

The amount as weU as the strength of acidity can be determined by titrating with basic solutions of different alkalinity (Boehm, et al., 1964 VoU and Boehm, 1970 Bandosz, et al., 1993 Boehm, 1994 Contescu et al., 1997 Biniak et al., 1997 Boehm, 2001 Boehm, 2002). The three types of acid groups above can be neutralized by 0.05 N solutions of, respectively, NaOH, Na2C03, and NaHC03 (known as Boehm titration). The acidity of any functional group is influenced by its local chemical environment, that is, the size and shape of the polyaromatic... 

Titration with benzethonium chloride in acid solution measures the sulphonated ester plus the sulphonated carboxylic acid, only the sulphon-ate group of the latter being titrated. In alkaline solution the titration measures the sulphonated ester plus twice the sulphonated carboxylate, both the sulphonate and the carboxylate group being titrated. Alpha-sulphonated esters give poor potentiometric titration curves, and two-phase titration is strongly preferred. 

With a-sulphonated fatty ester. Acid hydrolysis (section 5.11.4). Then BEC titration in alkaline solution. The increase over the result in acid solution measures the sum of a-sulphonated fatty acid already present and the hydrolysed a-sulphonated fatty ester. 

Any sulphate with a-sulphonated fatty ester. BEC titration in alkaline solution after acid hydrolysis gives twice the a-sulphonated ester (approximately—see above) plus any sulphonated hydrocarbon, less the sulphate. Determine the sulphate separately by measuring any one of its decomposition products. 

Carboxylates with quats. SDS titration in acid solution BEC titration in alkaline solution potentiometric acid-base titration in ethanol or propan-2-ol. 

Mm (aq) has a barely discernible pale pink color. Mn04 (aq) is an intense purple color. At the end point of the titration reaction (23.24), the solution acquires a lasting light purple color with just one drop of excess Mn04 (aq) (recall Figure 5-19). Mn04 (aq) is less satisfactory for titrations in alkaline solutions because the insoluble reduction product, brown Mn02(s), obscures the end point. 

By the evolution of ammonia with Devarda s alloy in alkaline solution in absence of ammonium ions this is used quantitatively, the ammonia being absorbed in excess standard acid and the excess acid back-titrated. 

In water pollution studies, the oxygen content can be measured by making the water alkaline and shaking a measured volume with an oxygen-free solution containing Mn- (aq). The solution is acidified with sulphuric acid, potassium iodide added and the liberated iodine titrated with sodium thiosulphate. 

Probably the most extensively applied masking agent is cyanide ion. In alkaline solution, cyanide forms strong cyano complexes with the following ions and masks their action toward EDTA Ag, Cd, Co(ll), Cu(ll), Fe(ll), Hg(ll), Ni, Pd(ll), Pt(ll), Tl(lll), and Zn. The alkaline earths, Mn(ll), Pb, and the rare earths are virtually unaffected hence, these latter ions may be titrated with EDTA with the former ions masked by cyanide. Iron(lll) is also masked by cyanide. However, as the hexacy-anoferrate(lll) ion oxidizes many indicators, ascorbic acid is added to form hexacyanoferrate(ll) ion. Moreover, since the addition of cyanide to an acidic solution results in the formation of deadly... 

Cyanide is determined at concentrations greater than 1 ppm by making the sample alkaline with NaOH and titrating with a standard solution of AgN03, forming the soluble Ag(CN)2 complex. The end point is determined using p-dimethylaminobenzalrhodamine as a visual indicator, with the solution turning from yellow to a salmon color in the presence of excess Ag+. 

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. 

Sodium thiosulfate is determined by titration with standard iodine solution (37). Sulfate and sulfite are determined together by comparison of the turbidity produced when barium chloride is added after the iodine oxidation with the turbidity produced by a known quantity of sulfate iu the same volume of solution. The absence of sulfide is iadicated when the addition of alkaline lead acetate produces no color within one minute. 

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