Ferric alum indicator solution

A 0.5-g. sample is dissolved in 50 ml. of 3 M aqueous ammonia, and the solution is made slightly acidic to litmus paper with 6 M nitric acid. Fifty milliliters of standard 0.1 M silver nitrate, 3 ml. of nitrobenzene, and 10 drops of ferric alum indicator are added, and the excess Ag+ is titrated with 0.1 M potassium thiocyanate to a brownish-red end point. 

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). 

Primary standard AgNOs is used to standardize a 0.1 M KSCN solution, using a ferric alum indicator. The unknown silver alloy is analyzed by titrating with the standardized KSCN solution. 

Provided. Primary standard AgN03, ferric alum indicator [KFe(S04)2 12 H2O, saturated solution], 6 M HNO3 (free of oxides of nitrogen). Nitric acid free from lower oxides of nitrogen should be colorless and can be prepared, if necessary, by boiling 1 1 HNO3 until NO2 is expelled. 

Transfer with a pipet two samples, 50 mL each, into 250-mL Erlenmeyer flasks, add 2 mL ferric alum indicator, and titrate with standard 0.1 M KSCN solution to the appearance of a faint reddish-brown color, which is permanent even after strong agitation. The two titrations should agree within... 

Five grams of precursor are refluxed for 1 h in about 200 cm distilled water, cooled, filtered and made up to volume in a 250 cm standard flask. An indicator is prepared by dissolving 500 g of ferric ammonium sulphate crystals in 700 cm distilled water. Now take 200 cm of this concentrated solution, add 400 cm concentrated HNO3 and making up to 1 litre with distilled water. Take a 10 cm aliquot and add 1 cm ferric alum indicator, measure the optical density in a spectrophotometer at 510 pm against a blank of 10 cm distilled water and 1 cm ferric alum indicator. The ppm level of NaSCN can be determined from a calibration graph. 

Pipet out 20 ml of standard N/20 AgN03 solution into a titration flask and add 5 ml of dilute HNO3 and 1 ml of ferric alum indicator. Titrate against KSCN solution until a permanent faint reddish-brown colour appears. Repeat to get concordant readings. 

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. 

Yolumetrically, thiocyanate is estimated by Volhard s method, which involves titration with standard silver nitrate solution containing nitric acid, ferric alum being used as indicator. Cuprous thiocyanate dissolved in ammonium hydroxide solution and acidified with dilute sulphuric acid may be titrated with permanganate.6 An iodometrie method has also been described.7... 

This energetic reducing agent can be maintained at constant strength in aqueous hydrochloric acid solution for a reasonable period. It is advisable, however, to re-standardise it after 24 hours standing. It serves for the reduction of aromatic nitro compounds, some nitroso bodies, many azo dyes, and of nearly all the dyes which yield leuco-compounds. It is easily standardised against a ferric salt—say ferric alum—using potassium thiocyanate as indicator. From the equations —... 

Volumetric estimation4 in neutral solution can be effected by titration with standard sodium chloride, potassium chromate being employed as indicator and in nitric-acid solution with thiocyanate, using ferric alum as indicator, or with sodium chloride without any external indicator. 

Argentometric titration method has been applied to the determination of sulfonamide mixtures. The sulfonamides are quantitatively precipitated by the addition of excess standard silver nitrate solution, the precipitated silver salts removed by filtration, and the excess silver nitrate titrated with standard ammonium thiocyanate using ferric alum as indicator (32). 

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. 

Indicator solution. Dissolve 40 g of ammonium iron(III) sulphate dodecahydrate (ferric alum) in a mixture of 20 cm of nitric acid water (3 5 v.v) and 80 cm of water. Heat to boiling and dilute with 3 volumes of water. 

To a mixture of 50 ml of water, 3 ml of dilute ammonia solution and 6 ml of 10 per cent ammonium nitrate solution add 0 8 g of sample, warm on a water-bath for fiye minutes and add 25 ml of 01N silver nitrate. Warm for fifteen minutes, shaking frequently, cool, dilute to 200 ml with water and allow to stand for sixteen hours. Filter, wash the residue with water, neutralise the combined filtrate and w-ashings to litmus paper with concentrated nitric acid and add 3 ml of the acid in excess. Titrate the excess silyer nitrate with 0-1N ammonium thiocyanate using ferric alum as indicator. 1 ml 0 1N silyer nitrate = 0 02146 g C H OaN Cl. 

To a solution in ethanol, containing approximately 0 01 g of glyceryl trinitrate and through which is passing a current of carbon dioxide to expel air, add 25 ml of approximately 0-05N titanous chloride. Set aside for ten minutes, then boil for ten minutes and finally cool in ice for ten minutes. Titrate the excess of titanous chloride with 0 05N ferric alum using 5 ml of 5 per cent ammonium thiocyanate solution as indicator. Carry out a blank experiment simultaneously. 1 ml 0 05N = 0 000631 g of nitroglycerin. 

For back-titration the method of Volhard is used and is probably the most widely employed technique for determination of halide ions. The halide is precipitated from a nitric acid solution by addition of excess silver nitrate and the excess is back-titrated with ammonium thiocyanate using ferric alum as indicator at the end-point the blood-red ferric thiocyanate is formed. Since silver thiocyanate is much less soluble than silver chloride, ammonium thiocyanate will attack the silver chloride precipitate and so cause erroneous results. For this reason the silver chloride must be removed or protected before titration of the excess silver nitrate is begun. This is best obtained by filtering off the precipitate before back-titration, but this step is time-consuming. As an alternative, some organic solvent may be added which will form a protective coating around the silver chloride and for this purpose nitrobenzene appears to be the most satisfactory. It should be remembered, however, that nitrobenzene is a powerful... 

To about 0-5 g add 25 ml of O IN silver nitrate. After the addition of 10 ml of dilute nitric acid and heating on a water-bath for thirty minutes the salt is completely decomposed and the silver iodide precipitated. Titrate the excess of silver nitrate with 0 1 N potassium thiocyanate solution, using ferric alum as indicator. 1 ml O IN = 0 01269 g I. 

Procedure for titrating mercury—Amounts of mercury greater than 50 mg— Wash the receiver free from tarry matter by adding acetone through the B14 socket, and then wash several times with water to remove acetone. Detach the glass-wool trap, and transfer the receiver to a wide-necked 500-ml conical flask. Add 15 ml of water and then 15 ml of concentrated nitric acid, slowly at first, until most of the zinc dissolves. Warm on a water-bath to dissolve the mercury, and then boil to remove nitrous fumes. Add 5 per cent potassium permanganate solution, dropwise, until a permanent pink colour is obtained, cool and decolorise with a trace of ferrous sulphate. Dilute with water to about 120 ml, cool to below 15°, and titrate with 0 1 N ammonium thiocyanate using ferric alum as indicator. 1 ml 0-lN = 0 01003 g Hg. 

Weigh 0-5 g into a 100-ml Kjeldahl flask, add 5 ml of concentrated sulphuric acid and heat gently until charred. Continue to heat and add strong hydrogen peroxide solution, dropwise, until colourless. Dilute, evaporate until slight fuming occurs, dilute to 10 ml with water and titrate with 01N ammonium thiocyanate using ferric alum as indicator. 1 ml 0-lN = 0 02024 g. 

Silver ions in a solution containing free nitric acid can be titrated with a standard solution of KSCN or NH4SCN using a solution of ferric alum or ferric nitrate as indicator (Volhard method). When thiocyanate solution is added, a white precipitate of silver thiocyanate results ... 

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