Direct titration with sodium hydroxide solution

1 Direct titration with sodium hydroxide solution 

The method is based on the conversion of carbon dioxide with sodium hydroxide solution to sodium hydrogen carbonate  

Following complete conversion, the pH of the sodium hydrogen carbonate 

The method is suitable for the determination of CO2 concentrations up to 200 mg/1 in natural waters. If concentrations are higher, CO2 losses may occur during titration. Waters of this type should be analyzed using the 

In waters with sizeable concentrations of Ca(HC03)2, interference may be caused by the precipitation of calcium carbonate. This may be prevented by adding 30 % Seignette salt solution which has been set to pH 8.3. 

---

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... 

The structural formula reveals that this polymer contains two different types of carboxyl group which have different dissociation constants. While the first dissociation step is characterized by a pK value of 3.4, the pK value of the second step is about 7.4. Both pK values were determined via titration of the prepolymer with sodium hydroxide solution. The exchange capacity of the finished stationary phase is directly proportional to its polymer content. It may be calculated in advance, since, owing to the chemical composition, the concentration of the exchange groups in the prepolymer is known. 

Direct titration of CO2 with sodium hydroxide solution and conversion to sodium hydrogen carbonate has proved suitable as a determining process on site. The end-point of titration is at pH 8.3 and can either be determined electrometrically with the aid of a glass electrode and a pH meter or visually by using phenolphthalein. The process is suitable for direct... 

Free Fatty Acids (as oleic acid) Determine as directed under Free Fatty Acids, Appendix VII, using 28.2 as the equivalence factor (e) in the calculation for oleic acid. Titrate with the appropriate normality of sodium hydroxide solution, shaking vigorously, to the first permanent pink color of the same intensity as that of the neutralized alcohol (if the sample color interferes, titrate to a pH of 8.5, determined with a suitable instrument). 

When the interferents cannot be easily masked, or eliminated, then bromide can be removed from the sample as BrCN by distillation and quantitatively absorbed in sodium hydroxide solution. BrCN can be decomposed by sulfuric acid and the bromide content measured by titration with silver nitrate reagent, or by direct potentiometry. Chloride or iodide content of the sample does not interfere with the determination. 

A convenient method for quantitation of free fatty acids in plasma, incubation mixtures, tissue homogenates etc. was introduced by Dole (1956), according to which the free fatty acids are extracted directly with an isopropanol-heptane mixture from acidified samples. Further addition of heptane and water results in formation of a two-phase system. Aliquots of the upper heptane phase containing the free fatty acids are titrated with a dilute solution of aqueous sodium hydroxide. 

At the end of the transformation, acetic anhydride in excess is hydrolyzed in acetic acid, which is directly titrated in the reaction medium with a sodium hydroxide solution in the presence of phenolphthalein. The same operations are realized with a blank in which there is no hydroxylated derivative, all the other experimental conditions being the same as in the assay. The difference between both volumes added gives the number of moles of acetic acid used for the esterification. The in pyridine acetylation index is of great interest in the analysis of essential vegetable oils, fats, and numerous pharmaceutical compounds, including, for instance, the determinations of cetylic and benzylic alcohols. The propionyl index is based on the same principle, but all of the operations are performed in a nonaqueous medium. 

Sodium antimonylgluconate is a trivalent antimony derivative. The total antimony is determined after wet combustion by reduction with potassium iodide in the presence of tartaric acid, boiling off the iodine completely, making alkaline with sodium hydroxide, then just acid with dilute sulphuric acid, and titrating in bicarbonate solution with 0-05N iodine. 1 ml = 0 003044 g Sb. Trivalent antimony can be determined polarographically as described above directly on the material. 

Dextromethorphan hydrobromide, CigH250N,HBr,H20, Mol. Wt. 370-3, is assayed in the B,P,C, by extracting about 0-3 g with chloroform from sodium hydroxide solution and titrating the extracts directly with 0-02N perchloric acid using methyl red as indicator, 1 ml 0-02N = 0-007047g of Ci8H250N,HBr. 

In the direct method, a solution of the ammonium salt is treated with a solution of a strong base (e.g. sodium hydroxide) and the mixture distilled. Ammonia is quantitatively expelled, and is absorbed in an excess of standard acid. The excess of acid is back-titrated in the presence of methyl red (or methyl orange, methyl orange-indigo carmine, bromophenol blue, or bromocresol green). Each millilitre of 1M monoprotic acid consumed in the reaction is equivalent to 0.017032 g NH3 ... 

If it is desired to base the standardisation directly upon arsenic(III) oxide, proceed as follows. Weigh out accurately about 0.20 g of pure arsenic(III) oxide into a conical flask, dissolve it in 10 mL of 1M sodium hydroxide, and add a small excess of dilute sulphuric acid (say, 12-15 mL of 0.5M acid). Mix thoroughly and cautiously. Then add carefully a solution of 2 g of sodium hydrogencarbonate in 50 mL of water, followed by 2 mL of starch solution. Titrate slowly with the iodine solution to the first blue colour. Repeat with two other similar quantities of the oxide. 

In essence, aqueous titration of surface acidity is an ion-exchange process in which hydrated surface protons are replaced by other hydrated cations (e.g., Na+, NIV") during the course of the titration. The procedure is straightforward. It usually consists of the direct titration of an aqueous suspension of the sample of powdered solid with a dilute base (e.g., sodium hydroxide) to a neutral endpoint. Another commonly used procedure consists of noting the pH of an appropriate salt solution (e.g., ammonium acetate), adding the sample, and measuring the amount of di-... 

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). 

Assay Dissolve about 1 g of sample, accurately weighed, in 50 mL of water, add 50.0 mL of 0.05 M disodium EDTA and 20 mL of pH 4.5 buffer solution (77.1 g of ammonium acetate and 57 mL of glacial acetic acid in 1000 mL of aqueous solution), and boil gently for 5 min. Cool, and add 50 mL of alcohol and 2 mL of dithizone TS. Back titrate with 0.05 M zinc sulfate to a bright rose-pink color. Perform a blank determination (see General Provisions), and make any necessary correction. The milliliters of 0.05 M disodium EDTA consumed is equivalent to 50 minus the milliliters of 0.05 M zinc sulfate used. Each milliliter of 0.05 M disodium EDTA is equivalent to 23.72 mg of A1K(S04)2T2H20. Ammonium Salts Add 1 g of sample to 10 mL of 1 N sodium hydroxide in a small beaker, and heat on a steam bath for 1 min. The odor of ammonia is not perceptible. Fluoride Determine as directed in Method V under Fluoride Limit Test, Appendix IIIB. 

---