Acetic acid titrations

Procedure (iodometric method). Weigh out accurately about 5.0 g of the bleaching powder into a clean glass mortar. Add a little water, and rub the mixture to a smooth paste. Add a little more water, triturate with the pestle, allow the mixture to settle, and pour off the milky liquid into a 500 mL graduated flask. Grind the residue with a little more water, and repeat the operation until the whole of the sample has been transferred to the flask either in solution or in a state of very fine suspension, and the mortar washed quite clean. The flask is then filled to the mark with distilled water, well shaken, and 50.0 mL of the turbid liquid immediately withdrawn with a pipette. This is transferred to a 250 mL conical flask, 25 mL of water added, followed by 2 g of iodate-free potassium iodide (or 20 mL of a 10 per cent solution) and 10 mL of glacial acetic acid. Titrate the liberated iodine with standard 0.1M sodium thiosulphate. 

Would bromcresol green be an appropriate indicator for an acetic acid titration Explain. 

In aqueous solutions, whenever protonation equilibria are involved, the autoprotolysis of water needs to be incorporated into the model. Thus, for an acetic acid titration the model comprises two equilibria... 

Add 5 ml of an approximately 0.5 m ethereal solution of lithium aluminium hydride to 50 ml of a standardised approximately 0.2 m iodine solution in benzene. Shake the solution gently and allow to stand for 5 minutes, add 50ml of distilled water followed by about 2 ml of glacial acetic acid. Titrate the excess of iodine with a standardised 0.2 m solution of sodium thiosulphate using starch solution in the final stages to determine the end-point. 

Dissolve about 240 mg of sample, accurately weighed, in 75 ml of glacial acetic acid. Titrate with standardized 0.1 N perchloric acid in acetic acid to a potenticmetric endpoint using glass-calcmel electrodes. Each ml of 0.1N perchloric acid is equivalent to 25.234 mg of cimetidine. 

Assay Dissolve about 200 mg, accurately weighed, in 3 mL of formic acid and 50 mL of glacial acetic acid. Titrate with 0.1 A perchloric acid in glacial acetic acid, determining the endpoint potentiometrically. Perform a blank determination (see General Provisions), and make any necessary correction. Each mL of 0.1 Aperchloric acid is equivalent to 10.51 mg of C3H7NO3. 

The equivalent volume is readily determined in the laboratory by using an indicator that changes color near pH 8.7, the pH at the equivalence point of the acetic acid titration. A suitable choice would be phenolphthalein, which changes from colorless to red over a pH range from 8.2 to 10.0. The slope of pH versus volume of strong base is less steep near the equivalence point for a weak acid than it is for a strong acid, so determination of the equivalent volume—and of the unknown weak acid concentration—is somewhat less accurate. 

The titration curve for 100 mL of 0.1 M acetic acid titrated with 0.1 M sodium hydroxide is shown in Figure 8.5. The neutralization reaction is... 

N and (c) 0.0001 N (titrated with NaOH) and (d) 0.001 N acetic acid (titrated with NH OH or KOH). B Various moderately weak acids with NaOH. 

The reaction progress was followed by titrating the unreacted carboxyl groups in samples removed from the reaction mixture at different times of reaction, with a standard methanolic potassium hydroxide solution. The oxirane groups were also titrated in some of the samples, using the hydrogen bromide in glacial acetic acid titration technique (21). 

Dissolve a sample containing about 0.5 meq total base in 50 mL acetic anhydride. Titrate potentiometrically, using a glass combination electrode, with 0.1 M HCIO4 in acetic acid. Titrate to the second, weak break. This value corresponds to the sum of the ethoxylated amide, ethoxylated amine, and ethoxylated ester. Dissolve a second portion of the sample, about five times as much as titrated above, in glacial acetic acid. Titrate potentiometrically with 0.1 M HCIO4 in acetic acid. This titration gives the sum of the ethoxylated amine and ethoxylated ester. Calculation ... 

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