Silver chloride thiocyanate

Add a known volume ofo oaM.AgNOj solution (in excess) and boil the solution until the silver chloride has coagulated. Filter through a conical 5 cm. funnel, ensuring that the filter-paper does not protrude above the r m of the funnel. Wash the silver chloride and the filter-paper several times with a fine jet of distilled water. To the united filtrate and washings add i ml. of saturated ferric alum solution. The solution should be almost colourless if it is more than faintly coloured, add a few drops of concentrated nitric acid. Then titrate with 0 02M-ammonium thiocyanate solution until the permanent colour of ferric thiocyanate is just perceptible. (Alternatively the chloride may be determined potentiometrically.)... 

When the excess of silver has reacted, the thiocyanate may react with the silver chloride, since silver thiocyanate is the less soluble salt, until the ratio [C1 ]/[SCN ] in the solution is 169 ... 

This will take place before reaction occurs with the iron(III) ions in the solution, and there will consequently be a considerable titration error. It is therefore absolutely necessary to prevent the reaction between the thiocyanate and the silver chloride. This may be effected in several ways, of which the first is probably the most reliable ... 

Discussion. The chloride solution is treated with excess of standard silver nitrate solution, and the residual silver nitrate determined by titration with standard thiocyanate solution. Now silver chloride is more soluble than silver thiocyanate, and would react with the thiocyanate thus ... 

The precipitate is curdy (compare silver chloride) and is readily coagulated by boiling. It is washed with dilute ammonium thiocyanate solution a little sulphurous acid or ammonium hydrogensulphite is added to the wash solution to prevent any oxidation of the copper)I) salt. 

Exposure of the silver chloride or bromide to light results in an increase in the nitrogen yield. This is to be expected, because the action of the light supplies nuclei for the catalyzed reaction. On the other hand, exposure of silver thiocyanate, which is relatively insensitive to the action of light, has little or no effect on the amount of nitrogen obtained on subsequent reduction with hydroxylamine. 

Nitrosyl chloride in carbon tetrachloride reacts with silver thiocyanate to form silver chloride and nitrosyl thiocyanate ... 

The purity of the crystallized product, determined volu-metrically by Volhard s method, exceeds 98%. In this procedure, 10 ml. of a 1% solution of methylisourea hydrochloride is acidified with a few drops of nitric acid and treated with 20 ml. of 0.1 N silver nitrate. After removal of the silver chloride by filtration, the excess of the silver nitrate is estimated with 0.1 TV thiocyanate solution, using ferric alum as indicator. Alternatively, 10-ml. portions of 0.1 N silver nitrate, acidified with nitric acid, may be titrated directly with the 1% methylisourea hydrochloride solution in the presence of tartrazine. 

Chloride is analyzed by some form of reaction with silver to form insoluble silver chloride. Direct titration of milk with silver nitrate yields erroneously high and variable results, and pre-ashing cannot be used because chloride is lost by volatilization. Satisfactory procedures involve adding an excess of standardized AgN03 directly to milk and back titrating with potassium thiocyanate (KSCN), using a soluble ferric salt as the indicator (Sanders 1939). 

Thiourea is tbimed by heating ammonium thiocyanate at 170°C. After about an hour, 25% conversion is achieved. With HQ, thiourea forms thiourea hydrochloride with mercuric oxide, thiourea forms a salt and with silver chloride, it forms a complex salt. 

Transfer 50 mL of filtrate to a 250-mL flask. Add 2 mL of 6 N nitric acid, 5 mL of nitrobenzene, and 10 mL of standardized 0.1 N silver nitrate solution. Shake the flask until the silver chloride coagulates. Prepare a saturated solution of ferric ammonium sulfate, and add just enough concentrated nitric acid to discharge the red color add 1 mL of this solution to the 250-mL flask to serve as the indicator. Titrate with 0.1 N ammonium thiocyanate solution that has been standardized against the silver nitrate solution until the color persists after shaking for 1 min. Calculate the weight percent of sodium chloride, P, by the equation... 

In practice this determination is carried out by adding to a weighed quantity of the chloropicrin in a small flask fitted with a condenser, an excess of an aqueous-alcoholic solution of sodium sulphite, prepared by dissolving 10 gm. sodium sulphite in 250 ml. water and diluting with an equal volume of ethyl alcohol. The liquid in the flask is then carefully heated so as to distil off all but about 10 ml. This is then diluted with water to 100 ml. and 10 ml. of nitric acid and an excess of a standardised solution of silver nitrate are added. The solution is then warmed to drive off the nitrous gases and to coagulate the silver chloride, and then cooled and the excess silver nitrate titrated with a solution of ammonium thiocyanate (ferric alum indicator). 

Silver chloride is more soluble than silver thiocyanate. As a consequence, in chloride determinations by the Volhard method, the reaction... 

Small amounts of chloride can be separated from many other elements by precipitation, as silver chloride, from dilute HNO3 [1]. Bromide, iodide, and thiocyanate are also precipitated. Chloride has been separated as PbCb with lead phosphate as a collector [2]. 

Precipitation of silver azide from acetate solution and gravimetric determination of the silver as silver azide or silver chloride, or volumetrically by addition of an excess of standard silver nitrate solution and back-titration with standard ammonium thiocyanate using ferric alum as internal indicator. 

Light yellow, odorless powder slowly darkened by light. Crystals are hexagonal Or cubic, d 5.67 mp 552. Practically insol in water (0.03 mg/l) in acid (except coned HI in which it dissolves readily on heating) in ammonium carbonate. Freely sol in solns of alkali cyanides or iedides 35 mg dissolve in a liter of 10% ammouia appreciably sol in coned solns of alkali bromides, chlorides, thiocyanates, thiosulfates, mercuric and silver nitrates. It is slowly attacked by boiling coned acids, but not affected by hot solns of alkali hydroxides. 

This method of silver recovery can be applied to any silver precipitates from quantitative analysis, such as silver chloride, bromide, or thiocyanate. First wash the residues well with water by decantation and on the Buchner funnel, then spread out on paper to dry. A little nitrobenzene absorbed on the precipitate from the Volhard titration will not do any harm the greater part of the nitrobenzene will be removed by washing, in any case. 

Silver(I) bromide Silver(I) carbonate Silver(I) chloride Silver(I) chromate Silver(I) cyanide Silver(I) fluoride Silver(I) iodide Silver(I) nitrate Silver(I) nitrite Silver(I) oxide Silver(I) phosphate Silver(I) sulfate Silver(I) thiocyanate Silver(II) oxide Sodium Sodium acetate Sodium bromate Sodium bromide Sodium carbonate Sodium chlorate Sodium chloride Sodium dichromate Sodium fluoride Sodium hydrogen phosphate Sodium hydroxide (aq) Sodium iodate Sodium iodide Sodium nitote Sodium nihite Sodium oxide Sodium peroxide Sodium sulfate Sodium sulfate decahydrate Sodium sulfide Sodium teh aborate Strontiimi Sh ontiimi bromide Sh ontiimi bromide hexahych ate Sh ontiimi carbonate Sh ontiimi chlorate Sh ontiimi chloride Sh ontiimi chloride hexahych ate Sh ontiimi chromate Sh ontiimi fluoride Sh ontiimi hydroxide Sh ontiimi iodate Sh ontiimi iodide Sh ontiimi nitote... 

Potassium acid oxalate Potassium alum dodecahydrate Potassium bromide Potassium carbonate Potassium manganate Potassium perchlorate Potassium permanganate Potassium persulfate Potassium thiocyanate PVP Pyrogallol Quinone Resorcinol Silver Silver chloride... 

Chloride, Titrimetric (the lower limit of determination is 0.001 g as chloride) The sample is diluted, acidified, and treated with a small excess of standard silver nitrate solution. The precipitated silver chloride is removed by filtration and the excess silver nitrate is titrated with. standard ammonium thiocyanate solution using ferric ammonium sulfate indicator. 

Silver chloride Cuprous iodide Cuprous thiocyanate Lead chloride Cuprous chloride... 

Cathode Silver chloride Lead chloride Cuprous iodide Cuprous thiocyanate Cuprous chloride"... 

For our purposes, let s recall that silver forms poorly soluble compounds in water, except for silver nitrate, perchlorate, fluoride, acetate, and chlorate. It forms very insoluble compounds such as silver chloride (Ks = 10 - ), bromide (K = 10 X iodide (.K s = 10 - ), and thiocyanate (/fs = 10 " ). It also forms very insoluble derivatives with the cyanide ion CN, i.e., AgCN (Ks = 10 " ), and silver dicyanosilverate(I), silver argentocyanide (Ks = 10 ). It gives weakly soluble salts with some anions such as arsenite, phosphate, and chromate anions. Argentometry encompasses four great titration methods ... 

In order to determine chloride ions, it is necessary to remove the silver chloride precipitate, for example, by filtration or by centrifugation, before carrying out the back titration with thiocyanate ions. The reason is the following after the addition of an excess of silver ions, the precipitation of chloride ions as silver chloride may be considered complete because of the common ion effect. During the second stage of the determination, the excess of silver ions disappears with the addition of thiocyanate ions. Close to the equivalence point of the back titration, when both precipitates coexist, the following solubility products are satisfied simultaneously ... 

Fig. 37.1 Error made in the determination of chloride ions by Charpentier-Volhard s method when the silver chloride precipitate is not removed before the addition of thiocyanate ions...

Hence, we see that if we do not remove the silver chloride precipitate, an excess of thiocyanate ions is added and the chloride ions determination is endowed with a... 

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