Phenolphthalein as indicator

It is essential to standardise the alcoholic potassium hydroxide solution immediately before use by titration with standard 0-5N or 0-25N hydrochloric or sulphuric acid using phenolphthalein as indicator. 

If crude anthranilic acid is employed, it should be titrated against standard alkali with phenolphthalein as indicator, and the weight adjusted in accordance with the purity. 

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. 

C HsCOOH 122.125 Pure benzoic acid is available from NIST (National Institute for Science and Technology). Dissolve 0.5 g in 20 mL of neutral ethanol (run a blank), excluding CO2, add 20-50 mL, and titrate using phenolphthalein as indicator. 

Fill a 250 mL separatory funnel with ca 0.25M sodium sulphate solution. Allow this solution to drip into the column at a rate of about 2 mL per minute, and collect the effluent in a 500 mL conical flask. When all the solution has passed through the column, titrate the effluent with standard 0.1 M sodium hydroxide using phenolphthalein as indicator. 

Benzoic acid is sparingly soluble in water (which is a disadvantage) and must therefore be dissolved in 95 per cent ethanol. The mode of use is similar to that already described for potassium hydrogenphthalate (Section 10.27, Procedure B). For a 0.1 M solution, of, say, sodium hydroxide, weigh out accurately 0.4 g portions of the acid into a 250 mL conical flask, add 10- 20 mL of ethanol, shake until dissolved, and then titrate the solution with the strong alkali using phenolphthalein as indicator. A blank test should be made with the same volume of ethanol and the indicator deduct, if necessary, the volume of the alkali solution consumed in the blank test. 

Procedure. To determine the purity of a sample of boric acid, weigh accurately about 0.8 g of the acid, transfer quantitatively to a 250 mL graduated flask and make up to the mark. Pipette 25 mL of the solution into a 250 mL conical flask, add an equal volume of distilled water, 2.5-3 g of mannitol or sorbitol, and titrate with standard 0.1 M sodium hydroxide solution using phenolphthalein as indicator. It is advisable to check whether any blank correction must be made dissolve a similar weight of mannitol (sorbitol) in 50 mL of distilled water, add phenolphthalein, and ascertain how much sodium hydroxide solution must be added to produce the characteristic end point colour. 

Either the Mohr titration or the adsorption indicator method may be used for the determination of chlorides in neutral solution by titration with standard 0.1M silver nitrate. If the solution is acid, neutralisation may be effected with chloride-free calcium carbonate, sodium tetraborate, or sodium hydrogencarbonate. Mineral acid may also be removed by neutralising most ofthe acid with ammonia solution and then adding an excess of ammonium acetate. Titration of the neutral solution, prepared with calcium carbonate, by the adsorption indicator method is rendered easier by the addition of 5 mL of 2 per cent dextrin solution this offsets the coagulating effect of the calcium ion. If the solution is basic, it may be neutralised with chloride-free nitric acid, using phenolphthalein as indicator. 

When performing the two-phase titration with benzethonium chloride in alkaline medium and in the presence of phenolphthalein as indicator, not only the monosulfonates but also the di- and polysulfonates are determined [19]. The content of di- and polysulfonates is the difference between two titration results giving the amounts of total sulfonates and monosulfonates. Identifying the endpoint requires some experience. 

For each condition change, product samples were collected in regular (usually 1 hour) intervals at the output of the pressure regulator. Sampling time was adjusted to obtain about 10 g of the reaction mixture. After weighing, the sample was diluted with 50 ml iPrOH to achieve a homogeneous clear liquid. Acid content was determined by titration with NaOH solution in iPrOH using phenolphthalein as indicator. 

Since one of the product is acetic acid, the progress of reaction may be studied by titrating a known volume of reaction mixture against a standard alkali solution using phenolphthalein as indicator. Let V0, Vt and V, be the volumes of alkali required for titrating 10 ml of reaction mixture at zero time, at any time t and at the completion of the reaction, respectively. 

The substance is hydrolysed by boiling under reflux with 50 per cent sulphuric acid and the acetic acid or benzoic acid produced is distilled in steam and titrated with sodium hydroxide solution, using phenolphthalein as indicator. 

When the hydrolysis is complete carefully wash out the condenser with 10-12 c.c. of water. Then distil up to 5 c.c. of liquid into a small conical quartz flask. Use the condenser in the downward position and if necessary add a few boiling capillaries to the liquid in the flask. Repeat the distillation three more times, each time adding 7 c.c. of water. Test the distillate (volume about 20 c.c.) with some barium chloride for sulphuric acid (none should be present), boil for seven to eight seconds and titrate at once with 0-033 N sodium hydroxide solution 1 from a micro-burette having 0-02 c.c. scale-divisions. Use phenolphthalein as indicator and continue the titration until the colour becomes just pink and remains so for a few seconds. For the second titration distil 2 x 7 or 3 x 7 c.c. and for the third and fourth titrations only about 7 c.c. on each occasion. 

To determine the saponification value 1 of a fat 0-5-1-0 g. is boiled under reflux condenser for half an hour with 10 c.c. of 0-5 A-alcoholic KOH solution and the excess of alkali is then titrated with 0-5 2V-HCI, and phenolphthalein as indicator. 

Method of Willstatter and Waldschmidt-Leitz. Direct titration in alcoholic solution with 0-1 A-alkali using phenolphthalein as indicator. 

Busulphan is first hydrolyzed by refluxing it with water and two moles methanesulphonic acid (from one mole of Busulphan) thus generated, titrated with 0.1 N sodium hydroxide employing phenolphthalein as indicator. Hence, the equivalent weight of busulphan is 123.145 g. Therefore, each millilitre of 0.1 N sodium hydroxide is equivalent to 0.01232 g of busulphan. 

Each of the above liquid residues was tritrated against standard sodium hydroxide, using phenolphthalein as indicator. Identical titer values were obtained the same titer value was also given by the original solid residue of unreacted TBTA (0-1). Such an observation of identical titer Values should be expected if the conversion of TBTA, by reaction with sodium chloride, is solj.ly to TBTCl. However, any side reaction leading to TBT hydroxide or TBTO will result in lower titer values since these tin compounds, unlike TBTA or TBTCl cannot be titrated like weak acids. Clearly, the side reactions are not noticeable in these experiments. Hydrolysis is not competitive under the conditions of this study, probably because chloride concentration never drops below 10-1 whereas hydroxide concentration is always below 10 s. (It was noticed that the pH of the aqueous layer in each case had risen from 6.5 to 9.0.)... 

The detection and determination ot the perchlorates.—The perchlorates give no precipitates with silver nitrate or barium chloride soln. cone. soln. give a white crystalline precipitate with potassium chloride. Unlike all the other oxy-acids of chlorine, a soln. of indigo is not decolorized by perchloric acid, even after the addition of hydrochloric acid and they do not give the explosive chlorine dioxide when warmed with sulphuric acid unlike the chlorates, the perchlorates are not reduced by the copper-zinc couple, or sulphur dioxide. Perchloric acid can be titrated with —iV-alkali, using phenolphthalein as indicator. The perchlorates can be converted into chlorides by heat and the chlorides determined volumetrically or gravimetrically they can be reduced to chloride by titanous sulphate 28 and titration of the excess of titanous sulphate with standard permanganate they can be fused with zinc chloride and the amount of chlorine liberated can be measured in terms of the iodine set free from a soln. of potassium iodide and they can be... 

Next, 1.5 kg of sodium azide is added as a 2.7-3.0% aqueous solution. The solution should be alkaline (50 cm3 Gf solution should require 8-10 cm3 1.0 N H2S04 for neutralization using phenolphthalein as indicator). If the alkalinity is too low, a calculated amount of NaOH should be added to the solution. The above-mentioned quantity of sodium azide is poured into the reactor for 1 hr, maintaining a temperature of 50°C. 

Hydrogen chloride, passed through a Sicapent (E. Merck) drying tube, was fed into 500 mL of methanol (Note 10) over a period of 15 min at 0°C. The titer of the solution (7.5 N) was determined by titration with 1.0 N sodium hydroxide, Titriplex Merck-Schuchardt, Hohenbrunn, Germany against phenolphthalein as indicator. 

---