Titrations concordant results

A rough titration is usually carried out, followed by more accurate titrations until concordant results are obtained. Concordant results are within either 0-1 or 0-2 cm of each other, depending on the accuracy required. The mean or average value of the concordant results is used in the calculations. 

In an experiment to determine the percentage of nickel In hydrated nlckel(ll) sulfate, 2-63 g of the nlckel(ll) sulfate were weighed accurately, dissolved In water and diluted to 100 cm in a standard flask. A 20-0 cm volume of this solution was pipetted Into a conical flask along with an indicator solution. This solution was titrated against a 0-100 mol fi EDTA solution until the end-point was observed. The titrations were repeated until concordant results were obtained. 

A 1-50 g mass of aspirin was hydrolysed with 25-0 cm of 1-00 mol NaOH solution. After the hydrolysis was complete, the reaction mixture was transferred, with rinsings, to a 250 cm standard flask and made up to the graduation mark with distilled water. The solution was mixed thoroughly and 25-0 cm was pipetted Into a conical flask, along with a few drops of phenolphthalein Indicator. This was titrated with 0-0500 mol sulfuric add solution until the end-point of the titration was Indicated by the colour change from pink to colourless. The titrations were repeated until concordant results were obtained. 

The titration is then repeated, all but 2 c.cs. of the volume of glucose solution used in the first determination being run in at once, and the remainder in drops until the blue colour just vanishes. The end point is more easily observed when the dish is slightly tilted. Several determinations are made until concordant results are obtained. If the end point is indistinct, a dilute acetic acid solution of potassium ferrocyanide spotted on a white plate may be used as external indicator. A brown coloration is observed so long as copper is present in solution. 

ASCARIDOLE. The B,P.C. method for the determination of ascaridole is that of Cocking and Hymas based upon the oxidising action of the peroxide radical present in the molecule on a strongly acidified solution of potassium iodide and titration of the iodine liberated, under specified conditions. It was found necessary to resort to an empirical method based on the titration of pure ascaridole (standardised by titanous chloride—a method inapplicable to general determination as it has to be carried out in an inert atmosphere) as the reaction which takes place is complex and not yet fully understood. The conditions adopted result in the maximum liberation by a normal peroxide. Obviously, to obtain accurate and concordant results, it is essential to adhere strictly to the conditions laid down. 

Pipette 25.00 cm of standard 0.10 M calcium salt solution into a 250 cm conical flask. Dilute to about 100 cm and add 2 cm of the magnesium complexonate suspension (shake before use), 5 cm of the buffer solution (pH = 10) and 2-3 drops of Erochrome Black T indicator. Titrate with the approximately 0.1 M EDTA solution to a steel blue end point. Repeat to obtain concordant results. Calculate, from the average titre, the concentration of EDTA as mol dmAlternatively use accurately weighed 0.2 g purest calcium carbonate dried at 105 C, add water and dil. HCl to dissolve. Boil to expel carbon dioxide dilute to 100 cm and continue as above. 

Weigh out accurately about 0.8 g of the purest acid and make up to 250 cm with water in a volumetric flask. Pipette 25.0 cm of the solution into a conical flask, dilute to 50 cm with water, add a few drops of phenolphthalein and 3.0 g mannitol. Titrate with standard O.I M NaOH until the first pale red colour is detected. Repeat to obtain concordant results and calculate from the average titre the concentration of the acid in mol dm ... 

Titration of a mixture of carbonate and bicarbonate Prepare a solution which is 0.1 M in sodium carbonate and 0.05 M in sodium bicarbonate. Pipette 25.0 cm of the solution, add a few drops of thymol blue indicator and titrate with 0.2 M HCl as in Sec.5.3.2. Repeat to obtain concordant results. Repeat... 

Weigh out accurately about 0.4 g of purest potassium antimonate(V), add 30 cm cone. HCl then add a large excess of K1 solution in a distilling flask connected to 2 U tubes containing dilute KI. Heat to boiling until all the iodine passes to the U tubes. Combine their contents and rinsings in a conical flask. Titrate with standard 0.05 M thiosulphate solution until the solution is straw yellow. Add 2 cm of fresh starch solution and continue titration until the blue colour disappears for 1 minute. Repeat to obtain concordant results and calculate from the average titre, [Sb(V)] in mol dm. ... 

Because of the uncertainty in the exact water content of the purest sodium thiosulphate and because of the instability of its solutions due to traces of carbon dioxide in distilled water etc., it is essential to standardise solutions before use. Any turbidity in solutions due to the deposition of sulphur necessitates discarding the solution. The purest potassium iodate is >99.9% pure and can be dried at 120 C to remove any moisture. Weigh accurately about 3.5g of dried purest iodate, dissolve in water and make up to 1 dm in a volumetric flask. Pipette 25.0 cm of the solution into a conical flzisk, add 2 g of purest KI and shake well before adding 5 cm IM sulphuric acid solution. Titrate the liberated iodine with the thiosulphate solution as in Sec.7.3.1. Repeat to obtain concordant results and calculate the molar concentration of the thiosulphate solution. 

Using purest potassium or ammonium persulphate prepare 0.03 M solution. Pipette 25.0 cm of the solution into a 250 cm conical flask, add 3 cm of H3PO4 (syrupy), 10 cm dil. H2SO4 and 25.0 cm of 0.100 mol dm of iron(II) solution. After 5 minutes, titrate the excess Fe(II) with 0.02M KMn04 solution to the first permanent faint pink colour. Repeat to obtain concordant results. 

Prepare a 0.1 M silver nitrate solution and a solution which is O.OS M in NaCl and O.OS M in Nal. Pipette 25.0 cm of the mixed halide solution into a conical flask, add 10 drops of fluorescein indicator. Titrate with the silver nitrate solution while rotating the flask in diffuse daylight until the silver halides coagulate and a pink colour develops locally on the addition of the silver solution. Continue the titration until the precipitate suddenly assumes a permanent pink colour. Repeat to obtain concordant results. The titre gives the total halide concentration. Repeat the titration using diiododimethyl-fluorescein as indicator, when the precipitated compound assumes a permanent blue red colour. Repeat to obtain concordant results. The average titre in this case is equivalent to the iodide alone. Work out the difference between the titres using the two indicators, which corresponds to the chloride. Calculate [NaCl] and [Nal] in mol dm. ... 

Pipette 25.0 cm of the commercial NaOCl solution (Freshly supplied) into a 250 cm conical flask and add 50 cm water and 2 g KI, acidify with 10 cm glacial acetic acid and titrate the liberated iodine with standardised 0.05 M thiosulphate solution using starch indicator (Sec.7.3.1). Repeat to obtain concordant results. Calculate, from the average titre, [OCf] in mol dm" . 

Prepare 0.025 M L ascorbic acid solution by weighing accurately about 1.1 g of the purest solid, dissolving it and making up the solution in a 250 cm volumetric flask using boiled-out distilled deionised water. Pipette 10 cm of the solution into a conical flask, acidify with dilute sulphuric acid and add a few drops of N-phenylanthranilic acid indicator. Titrate with standardised freshly prepared Mn(lll) sulphate solution (as above) until the colour changes sharply to violet. Repeat to obtain concordant results and calculate, from the average titre, the ascorbic acid Mn(llI) molar ratio. 

Pipette 25.00 cm of the 0.1 M iron (II) solution, add 5 cm of 1 1 H3PO4 solution and 0.5 cm of diphenylamine sulphonate indicator solution. Titrate with standard M/60 dichromate solution until the colour changes sharply from green to dark violet. Repeat to obtain concordant results and calculate from the average titre the concentration of Fe(II) in g dm of solution. 

Pipette 25.00 cm of the Fe(ll) solution, previously prepared as described above, into a conical flask. Add 20 cm dil. H2SO4, 15 cm H2O and 2 drops ferroin indicator. Titrate with the standardised 6(804)2 solution until the colour changes sharply from orange red to a pale blue. Repeat the titration to obtain concordant results. Calculate, from the average titre, the concentration of Fe in g dm. ... 

Pipette 25.00 cm of the iron solution, add 5 cm of orfliophosphoric acid, 50 cm of water and a few drops of sodium N-methyIdiphenylamine sulphonate indicator solution and titrate with the dichromate solution until the end-point is marked by the appearance of a blue-violet colour. Repeat to obtain concordant results. 

Weigh out accurately 8.2 g purest K3[Fe(CN)6] into a beaker, dissolve in water and transfer quantitatively to a volumetric flask and make up to 250 cm. Pipette 25.0 cm of the solution into a 250 cm conical flask. Add 2 g K1 dissolved in 20 cm water and 15 cm of a solution containing 2 g ZnS04.7H20. Note the liberation of iodine. Titrate immediately with standardised 0.05 M diiosulphate solution until the colour is pale yellow. Then add 2 cm of freshly prepared starch solution and continue titration until the blue colour has just disappeared. Repeat to obtain concordant results. Calculate from the average litre the concentration of hexacyanoferrate(III) in mol dm. ... 

Weigh out accurately about 0.1 g of your preparation, dissolve in 30 cm of 0.1 M nitric acid. Heat until the solution changes colour to pink and no further colour change is observed. Add 1 cm of diphenylcarbazone/bromophenol blue indicator and titrate with 0.01 M mercuiy(Il) nitrate solution until the first tinge of blue purple does not disappear. Repeat to get concordant results. Calculate from the average results the % chloride and hence the percentage purity of your sample. (The chloride corresponds to the ionisable chloride + the chloride replaced by water on aquation (see below). 

Repeat the titration to obtain concordant results and calculate die concentration of Zn ions in the original solution in mol. dm and in g dm. ... 

Weigh out accurately about 0.25 g of your preparation into a conical flask. Add 50.0 cm of 0.1 M HCl from a burette followed by a few drops of methyl red indicator. Titrate with standard 0.1 M NaOH until the colour changes to yellow. Repeat to obtain concordant results. Calculate the average % purity of your preparation. 

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