Thiosulphates

The test is not applicable in the presence of sulphides and/or thiosulphates. These can be removed by the addition of mercury(II) chloride which reacts forming the acid-stable mercury(II) sulphide  

Place a drop of the test solution and 2 drops of saturated mercury(II) chloride solution in the same apparatus (Fig. 11.53) and, after a minute, acidify with 2m hydrochloric or m sulphuric acid, and proceed as above. 20 pg Na2S03 can be detected in the presence of 900 pg Na2S203 and 1,500 pg of Na2S. 

Distinction between sulphites and hydrogen sulphites The solution of normal alkali sulphites shows an alkaline reaction against litmus paper, because of hydrolysis  

SO2- + H202 - SO4- +H20 with hydrogen sulphites the same test yields hydrogen ions  

5 THIOSULPHATES, S2Of Solubility Most of the thiosulphates that have been prepared are soluble in water those of lead, silver, and barium are very sparingly soluble. Many of them dissolve in excess sodium thiosulphate solution forming complex salts. 

With hydrogen sulphites, the same test yields hydrogen ions  

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Sodium sulphide, NajS, formed by reduction Na2S04 with CO or H2- Aqueous solutions are oxidized to sodium thiosulphate. 

The liberated iodine is titrated with standard sodium thiosulphate(Vr) solution after acidification to remove the hydroxide ions. 

Colloidal sulphur is produced by careful addition of acid to sodium thiosulphate solution. 

However, the sulphide ion can attach to itself further atoms of sulphur to give polysulphide ions, for example Sj , Sj , and so these are found in solution also. Further, the sulphite ion can add on a sulphur atom to give the thiosulphate ion, S203 which is also found in the reaction mixture. 

Sodium thiosulphate is an important reducing agent used in volumetric analysis for the estimation of iodine ... 

In what way does a solution of hydrogen peroxide react with (a) chlorine water, (b) potassium permanganate solution, (c) potassium dichromate solution, (d) hydrogen sulphide 50 cm of an aqueous solution of hydrogen peroxide were treated with an excess of potassium iodide and dilute sulphuric acid the liberated iodine was titrated with 0.1 M sodium thiosulphate solution and 20.0 cm were required. Calculate the concentration of the hydrogen peroxide solution in g 1" ... 

The oxidation of the thiosulphate ion SjOj to tetrathionate ion, is used to estimate iodine. 

The ability of the solid chlorates(V) to provide oxygen led to their use in matches and fireworks. Bromates(V) and iodates(V) are used in quantitative volumetric analysis. Potassium hydrogen diiodate(V), KHflOjlj, is used to standardise solutions of sodium thiosulphate(Vf) since in the presence of excess potassium iodide and acid, the reaction... 

Alternatively, a known weight of the pyrolusite may be heated with concentrated hydrochloric acid and the chlorine evolved passed into potassium iodide solution. The iodine liberated is titrated with sodium thiosulphate ... 

In water pollution studies, the oxygen content can be measured by making the water alkaline and shaking a measured volume with an oxygen-free solution containing Mn- (aq). The solution is acidified with sulphuric acid, potassium iodide added and the liberated iodine titrated with sodium thiosulphate. 

Silver chloride is readily soluble in ammonia, the bromide less readily and the iodide only slightly, forming the complex cation [Ag(NH3)2]. These halides also dissolve in potassium cyanide, forming the linear complex anion [AglCN) ] and in sodium thiosulphate forming another complex anion, [Ag(S203)2] ... 

It was known in the sixteenth century that silver salts were photosensitive, but it was not until the beginning of the nineteenth century, when Herschel found that silver chloride was soluble in sodium thiosulphate, that photography became possible. 

The film is now fixed by washing in sodium thiosulphate ( hypo ) solution when the unchanged bromide is dissolved to form the complex ion... 

Required Ethanol, 30 ml. sodium, 14 g. iodine, 7 7 g. ethyl malonate, 9 ml. sodium thiosulphate solution. 

Now cork the flask securely, and shake it vigorously for about 5 minutes the solution should now have only a faint brown colour due to unchanged iodine. Cool the mixture in ice-water, pour it into a separating-funnel, and extract it twice with water to remove sodium iodide and most of the ethanol. Then shake the residual ethereal solution with a dilute aqueoussolution of sodium thiosulphate the excess of iodine is thus removed and the... 

Transfer 25 ml. of this dilute solution by means of a pipette to a conical flask, and add similarly 50 ml. of Ml 10 iodine solution. Now-add 10% sodium hydroxide solution until the liquid becomes pale yeilow in colour, and allow the solution to stand, with occasional shaking, at room temperature for at least 10 minutes. Then acidify with dilute hydrochloric acid (free from chlorine) in order to liberate the remaining iodine. Titrate the latter w ith Mho sodium thiosulphate solution, using starch as an indicator in the usual way. 

I he methyl iodide is transferred quantitatively (by means of a stream of a carrier gas such as carbon dioxide) to an absorption vessel where it either reacts with alcoholic silver nitrate solution and is finally estimated gravimetrically as Agl, or it is absorbed in an acetic acid solution containing bromine. In the latter case, iodine monobromide is first formed, further oxidation yielding iodic acid, which on subsequent treatment with acid KI solution liberates iodine which is finally estimated with thiosulphate (c/. p. 501). The advantage of this latter method is that six times the original quantity of iodine is finally liberated. 

Dibromobutane (from 1 4-butanediol). Use 45 g. of redistilled 1 4-butanediol, 6-84 g. of purified red phosphorus and 80 g. (26 ml.) of bromine. Heat the glycol - phosphorus mixture to 100-150° and add the bromine slowly use the apparatus of Fig. Ill, 37, 1. Continue heating at 100-150° for 1 hour after all the bromine has been introduced. Allow to cool, dilute with water, add 100 ml. of ether, and remove the excess of red phosphorus by filtration. Separate the ethereal solution of the dibromide, wash it successively with 10 per cent, sodium thiosulphate solution and water, then dry over anhydrous potassium carbonate. Remove the ether on a water bath and distil the residue under diminished pressure. Collect the 1 4-dibromobutane at 83-84°/12 mm. the yield 3 73 g. 

In a 500 ml. three-necked flask, equipped with a thermometer, a sealed Hershberg stirrer and a reflux condenser, place 32-5 g. of phosphoric oxide and add 115-5 g. (67-5 ml.) of 85 per cent, orthophosphoric acid (1). When the stirred mixture has cooled to room temperature, introduce 166 g. of potassium iodide and 22-5 g. of redistilled 1 4-butanediol (b.p. 228-230° or 133-135°/18 mm.). Heat the mixture with stirring at 100-120° for 4 hours. Cool the stirred mixture to room temperature and add 75 ml. of water and 125 ml. of ether. Separate the ethereal layer, decolourise it by shaking with 25 ml. of 10 per cent, sodium thiosulphate solution, wash with 100 ml. of cold, saturated sodium chloride solution, and dry with anhydrous magnesium sulphate. Remove the ether by flash distillation (Section 11,13 compare Fig. II, 13, 4) on a steam bath and distil the residue from a Claisen flask with fractionating side arm under diminished pressure. Collect the 1 4-diiodobutane at 110°/6 mm. the yield is 65 g. 

To determine the exact peroxide content of benzoyl peroxide (and of other organic peroxides) the following procedure may be employed. Place about 0 05 g. of the sample of peroxide in a glass-stoppered conical flask add 5-10 ml. of acetic anhydride (A.R. or other pure grade) and 1 g. of powdered sodium iodide. Swirl the mixture to dissolve the sodium iodide and allow the solution to stand for 5-20 minutes. Add 50-75 ml. of water, shake the mixture vigorously for about 30 seconds, and titrate the liberated iodine with standard sodium thiosulphate solution using starch as indicator. 

To determine the exact perbenzoic acid content of the solution, proceed as follows. Dissolve 1 -5 g. of sodium iodide in 50 ml. of water in a 250 ml. reagent bottle and add about 5 ml. of glacial acetic acid and 5 ml. of chloroform. Introduce a known weight or volume of the chloroform solution of perbenzoic acid and shake vigorously. Titrate the liberated iodine with standard O lA sodium thiosulphate solution in the usual manner. 

The m.p. is not always a safe criterion of purity. Benzoyl peroxide may be analysed as follows -. Dissolve about 0-6 g., accurately weighed, of benzoyl peroxide in Is ml. of chloroform in a 350 ml. conical flask. Cool to — 5°, and add 25 ml. of 0- IN sodium methoxide solution at once with cooling and shaking. After 5 minutes at — 5°, add 100 ml. of iced water, 5 ml. of 10 per cent, sulphuric acid, and 2 g. of potassium iodide in 20 ml. of 10 per cent, sulphuric acid in the order mentioned with vigorous stirring. Titrate the liberated iodine with standard 0-lN sodium thiosulphate solution. 

To determine the per-acid content, add 30 ml. of 20 per cent, po assium iodide solution to 2-0 ml. of the solution and, after 10 minutes, titrate the liberated iodine with standard 0-05N sodium thiosulphate solution (compare Perbemoic Acid, Section IV,198, Note 1). 

In order to prepare an acid, a dioxan solution of the diazo ketone is added slowly to a suspension of silver oxide in a dilute solution of sodium thiosulphate Iftheco)iversion to the acid yields unsatisfactory results, it is usually advisable to prepare the ester or amide, which are generally obtained in good yields hydrolysis of the derivative gives the free acid. 

Introduce a solution of 15 g. of the diazo ketone in 100 ml. of dioxan dropwise and with stirring into a mixture of 2 g. of silver oxide (1), 3 g. of sodium thiosulphate and 5 g. of anhydrous sodium carbonate in 200 ml. of water at 50-60°. When the addition is complete, continue the stirring for 1 hour and raise the temperature of the mixture gradually to 90-100°. Cool the reaction mixture, dilute with water and acidify with dilute nitric acid. Filter off the a-naphthylacetic acid which separates and recrys-talhse it from water. The yield is 12 g., m.p. 130°. 

Add, with stirring, a solution of 6 8 g. of the fiis-diazo ketone in 100 ml. of warm dioxan to a suspension of 7 0 g. of freshly precipitated silver oxide in 250 ml. of water containing 11 g. of sodium thiosulphate at 75°. A brisk evolution of nitrogen occurs after 1 5 hours at 75°, filter the liquid from the black silver residue. Acidify the almost colourless filtrate with nitric acid and extract the gelatinous precipitate with ether. Evaporate the dried ethereal extract the residue of crude decane-1 10-dicarboxylic acid weighs 4 -5 g. and melts at 116-117°. RecrystaUisation from 20 per cent, aqueous acetic acid raises the m.p. to 127-128°. 

HC5N (cyanodiacetylene) interstellar, 120 rotational spectrum, 110 Na2S203 (sodium thiosulphate)... 

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