Alkali titration determination

The reaction between equivalent amounts of acid and alcohol was studied at 166°C by Flory (JACS 6 1 3334, 1939] who followed the reaction by titration of weighed samples against standard alkali to determine the number of free carboxyl groups. Data of (t, f] are tabulated, where t is in minutes and f is the fraction of carboxyl groups esterifled. The order of the reaction is to be investigated. 

Carbon in soil and plant materials can be determined by wet- and dry-combustion methods [7, 8]. In both instances, soil and plant carbon is converted into carbon dioxide, absorbed in alkali and determined either by titration against a standard acid or by weighing. These methods involve large apparatus, are expensive and time consuming, and therefore cannot be adapted to the routine analysis of a large number of samples. 

Determination of Carboxylic Group Terminals. The carboxylic group terminals were determined by alkali titration (12.). After 200 mg of the sample was dissolved in T.5 ml of benzyl alcohol in a nitrogen atmosphere at 110 °C, the solution was titrated with 0.05N potasL- Vum hydroxide using phenolphthalein as an indicator. A blank test was carried out by the same method but omitting the sample. 

The alcoholic hydrogen chloride can be prepared by passing hydrogen chloride from a cylinder (use safety trap) into 200 ml. of absolute ethanol cooled by an ice bath. From time to time a sample may be withdrawn and titrated with standard alkali to determine the concentration. The exact amount is not critical, but a considerable excess of hydrogen chloride must be used. If several runs are to be made it is convenient to prepare a large quantity of alcoholic hydrogen chloride at one time. 

Permanent hardness can also be estimated by the alkalimetric method of Wartha and Pfeifer. A measured volume (200 e.e.) of the water is boiled with 50 c.e. of a mixture of decmormal solutions of sodium carbonate and hydroxide in equal amounts after restoring to the original volume and allowing the solution to settle, the residual alkali is determined by titration with standard acid. As the bicarbonates do not cause any consumption of alkali, there is a direct proportionality between the quantity of alkali which disappears and the total amount of sulphates and chlorides of calcium and magnesium. Sodium carbonate alone does not efficiently precipitate magnesium salts from solution, but precipitation as the hydroxide is complete if excess of sodium hydroxide is present it is for this reasoii that a mixture of sodium carbonate and hydroxide is applied 3 (see also p. 211). 

The titration of an acid solution with a standard solution of alkali will determine the amount of alkali which is equivalent to the amount of acid present (or vice versa). The point at which this occurs is called the equivalence point or end-point. For example, the titration of hydrochloric acid with sodium hydroxide can be expressed as follows ... 

The yield is 80-90%, determined as follows. A 5 or 10 mL aliquot of the solution is withdrawn by means of a pipet connected to a rubber suction bulb, and hydrolyzed by adding to distilled water (10 mL). This is titrated with standard acid to determine the total alkali, using phenolphthalein as indicator. A second 5 or 10 mL aliquot is withdrawn and run into a solution of anhydrous ether (10 mL) containing benzyl chloride (1 mL). The mixture is allowed to stand for 1 min after the addition and is then hydrolyzed with water (10 mL) and titrated with standard acid. Care must be taken not to overstep the end point since the aqueous layer becomes decolorized before the ether layer. To overcome this the mixture should be shaken vigorously near the end point. The second titration determines the alkali present in the form of compounds other than n-butyllithium. The difference between the two titration values represents the concentration of n-butyllithium. 

Halogen in organosilicon compounds may be either directly linked to silicon or may be part of a substituent group. Total halogen is usually determined by alkali fusion methods. Halogen attached directly to silicon is easily hydrolysable by aqueous alcohols and the halogen acid so produced can be estimated by direct alkali titration or by indirect procedures. 

An excess of hydrogen peroxide and of a solution of sodium hydroxide of known strength is added to the dilute solution of formalin. The excess of alkali is determined by titration with an acid, and from the amount of sodium hydroxide used in the reaction the weight of aldehyde can be calculated. 

Modern analytical instrumentation has been used in the last 23 years for determining commercially important characteristics of soluble silicates, and the nature of silicate species in silicate glasses and solutions. The classical wet methods for assay of silicate solutions are alkali titration and gravimetric determination of silica, which can also be determined, with lesser precision, by the alkali fluosilicate method. 

Silicate to soda ratios can also be determined rapidly for quality control purposes by an alkali titration and a measurement of either specific gravity or refractive index and viscosity which are correlated to Si02/Na20 ratios using control charts. The control charts are based on samples previously analyzed by the precise gravimetric method. The specific gravity method is more commonly used in commercial practice,... 

The use of an indicator in an acid-alkali titration is referred to in a monograph published in 1767 by William Lewis entitled Experiments and Observations on American Potashes with an Easy Method of determining their respective Qualities. He determined the point of saturation of the alkali by an acid by the change of colour produced in certain vegetable juices, or on a paper stained with them. Lewis advocated that the quantities of both solutions should be determined by weight. 

Her has carried out a hitherto unpublished investigation of the rates at which extremely small particles of colloidal silica depolymerize to monomer both directly in the molybdic acid reagent and in dilute alkali in which the monomer is determined on separate samples by reaction with molybdic acid. The size of the particles was estimated from the specific surface area, which was determined by the Sears alkali titration method corrected for monomer. The measurements were made as the particles grew in size at pH 8.5 and also as they became aggregated at pH 5.9. 

Determination of Fatty Acids in Cerebrospinal Fluid. II. Qualitative and Quantitative Studies by a Combination of Alkali Titration and Gas Chromatography Scand. J. Clin. Lab. Invest. 16(2) 139-144 (1964) CA 62 9605d... 

Unreacted sodium isethionate is the only other impurity likely to be present in significant amounts. It is determined by determining total anions by ion-exchange conversion to the corresponding acids and titration with alkali, then determining the active, soap and chloride contents and finding the isethionate by difference. 

Mixtures of mono- and diester and phosphoric acid can be determined by alkali titration. 

The phosphate esters are converted to the free acid form, if they are present as salts, and determined by alkali titration. Monoesters have one weakly acidic and one strongly acidic proton. Diesters are strongly acidic. 

Alkalinity, which is usually sodium carbonate, and may be somewhat considerable if the soap has been grained with caustic alkali, is determined after dilution with water by titrating with N/2 acid, using methyl orange as indicator. 

A commonly used method for determining acid content is alkali titration using an appropriate indicator [1-4], However, in this method, there is the possibility of error due to an inability to detect a subtle color change of the indicator in the transition range, especially in cases of colored samples. In addition, the titration method is not sufficiently sensitive to detect low acid content, and it requires large sample amounts and a great deal of time. Potentiometric titration is commonly recommended as an alternative method. 

If the ammonium salt being determined is fairly pure, an excess of N sodium hydroxide may be added to a known weight, the solution boiled until all ammonia is evolved and the excess of alkali titrated back with N acid to methyl orange. 1 ml N — 0 01703 g NH3. 

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. 

An ethanol/water solution of the sample is extracted with petroleum ether at pH 3 and the residue weighed. This fraction corresponds to the unsulfonated fatty acid and fatty acid ester. The extract is titrated with alkali to determine the fatty acid content, and the ester is determined by difference (120). 

Ammonia may be estimated by dissolving the gas in a known volume of standard acid and then back-titrating the excess acid. In a method widely used for the determination of basic nitrogen in organic substances (the Kjeldahl method), the nitrogenous material is converted into ammonium sulphate by heating with concentrated sulphuric acid. The ammonia is then driven off by the action of alkali and absorbed in standard acid. 

Although two isomeric esters are theoretically possible, the main product is the 2-ester (formulated above) traces of the isomeric l-ester are eliminated during purification. These derivatives possess a free carboxyl group their equivalent weights may therefore be determined by titration with standard alkali and thus serve as an additional check upon the identity of the compound. 

The saponiflcatlon equivalent or the equivalent weight of an ester is that weight in grams of the ester from which one equivalent weight of acid is obtainable by hydrolysis, or that quantity which reacts with one equivalent of alkali. The saponification equivalent is determined in practice by treating a known weight of the ester with a known quantity of caustic alkali used in excess. The residual alkali is then readily determined by titration of the reaction mixture with a standard acid. The amount of alkafi that has reacted with the ester is thus obtained the equivalent can then be readily calculated. 

These are crystalline compounds with sharp melting points, and possess the further advantage that their equivalent weights may be determined by dissolving in dilute alcohol and titrating with standard alkali. Nitro-phenols, however, give unsatisfactory derivatives. 

To determine the exact diazomethane content, allow an aliquot portion of the ethereal diazomethane solution to react with an accurately weighed amount (say, about 1 g.) of A. R. benzoic acid in 60 ml. of anhydrous ether. The solution should be completely decolourised, thus showing that the benzoic acid is present in excess. Dilute the solution with water and titrate the excess of benzoic acid with standard 0 IN alkali using phenolphthalein as indicator. 

Equivalent weight of an acid. Determine the equivalent weight of the acid (use about 0 2 g.) by titration with standard ca. 0- N alkali... 

The distillate is collected in a 500 c.c. Erlenmeyer flask having a mark upon it to indicate the level of 250 c.c. Phenolphthalein solution and a sufficient excess of deci-normal sodium hydroxide solution are added to the distillate and the excess of alkali determined by titration. 

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