Silver nitrate, solution preparation

An interesting extension of the above experiment is the titration of a mixture of halides (chloride/iodide) with silver nitrate solution. Prepare a solution (100 mL) containing both potassium chloride and potassium iodide weigh each substance accurately and arrange for the solution to be about 0.025 M with respect to each salt. A silver nitrate solution of known concentration (about 0.05 M) will also be required. 

Since the silver salts of the carboxylic acids are usually soluble in dilute nitric acid, they must be prepared by treating an aqueous solution of a neutral salt of the acid (and not the free acid itself) with silver nitrate solution. It is not practicable to attempt to neutralise the acid with sodium or potassium hydroxide solution, because the least excess of alkali would subsequently cause the white silver salt to be contaminated with brown silver oxide. The general method used therefore to obtain a neutral solution j to dissolve the acid in a small excess of ammonia solution, and then to boil the solution until all free... 

Ammoniacal Silver Nitr. te. Add 1 drop of 10% aqueous NaOH solution to about 5 ml. of silver nitrate solution in a test-tube then add dilute NHg drop by drop with shaking until only a trace of undissolved Ag O remains. A number of reductions require the presence of Ag " ions. It is often advisable, therefore, after adding the ammonia to add silver nitrate solution until a faint but permanent precipitate is obtained. The solution should always be prepared in small quantities immediately before use, and any unexpended solution thrown away afterwards. If the solution is kept for some time, it may form explosive by-products. 

Do not heat the silver solution or allow it to stand even for a few hours, since explosive silver fulminate may be formed. The ammoniacal solution of silver nitrate is prepared by treating 3 ml. of 0-lN silver nitrate solution with very dilute ammonia solution dropwise until the precipitate which is first formed just redissolves. 

Prepare the silver oxide by adding a dilute solution of sodium hydroxide to 10 per cent, silver nitrate solution until precipitation is just complete, avoiding an excess of edkali. Wash the precipitate several times by decantation finally, Ster at the pump and wash well with water. 

Reagents. Silver nitrate solution, 10 4M. Prepare by dilution of a standard 0.1 M silver nitrate solutioa... 

Pipette 25.0 mL of the bromide ion solution (0.01-0.02M) into a 400 mL beaker, add excess of dilute silver nitrate solution, filter off the precipitated silver bromide on a sintered glass filtering crucible, and wash it with cold water. Dissolve the precipitate in a warm solution prepared from 15 mL of concentrated ammonia solution, 15 mL of 1M ammonium chloride, and 0.3 g of potassium tetracyanonickelate. Dilute to 100-200 mL, add three drops of murexide indicator, and titrate with standard EDTA (0.01 M) (slowly near the end point) until the colour changes from yellow to violet. 

Method B. Prepare the solution and transfer 25 mL of it to a 250 mL conical flask as detailed under Method A. Add two to three drops of diphenylcarbazide indicator and titrate with standard 0.1M silver nitrate solution until a permanent violet colour is just produced. 

Procedure. Acidify the iodate solution (lOOmL containing ca 0.3 g of I03) (see Note) with sulphuric acid, and pass in sulphur dioxide (or add a freshly prepared saturated solution of sulphurous acid) until the solution, which at first becomes yellow, on account of the separation of iodine, is again colourless. Boil off the excess of sulphur dioxide, and precipitate the iodide with dilute silver nitrate solution as described in Section 11.64. Weigh as Agl. 

The indicator electrode must be reversible to one or the other of the ions which is being precipitated. Thus in the titration of a potassium iodide solution with standard silver nitrate solution, the electrode must be either a silver electrode or a platinum electrode in the presence of a little iodine (best introduced by adding a little of a freshly prepared alcoholic solution of iodine), i.e. an iodine electrode (reversible to I-). The exercise recommended is the standardisation of silver nitrate solution with pure sodium chloride. 

Prepare an approximately 0.1 M silver nitrate solution. Place 0.1169 g of dry sodium chloride in the beaker, add 100 mL of water, and stir until dissolved. Use a silver wire electrode (or a silver-plated platinum wire), and a silver-silver chloride or a saturated calomel reference electrode separated from the solution by a potassium nitrate-agar bridge (see below). Titrate the sodium chloride solution with the silver nitrate solution following the general procedure described in Experiment 1 it is important to have efficient stirring and to wait long enough after each addition of titrant for the e.m.f. to become steady. Continue the titration 5 mL beyond the end point. Determine the end point and thence the molarity of the silver nitrate solution. 

Silver nitrate is prepared by dissolving silver metal in dilute nitric acid. The solution is evaporated and residue is heated to dull red heat with concentrated nitric acid to decompose impurities such as copper nitrate. Residue then is dissolved in water, filtered, and recrystallized to obtain pure silver nitrate. 

Excess of Potassium Chloride. < >n adding a few drops of potassium chromate solution to It) ee. of the aqueous solution, prepared from h gm. of potassium bromide, dried at 100° (1., and dissolved in 100 ee. of water, the solution should not require more than 25.4 ee. of de.oinormal silver nitrate solution to produce a permanent rod color. 

Calcium Chlorides. —20 cc. of the 1 20 aqueous solution prepared by the aid of heat should not be affected by ammonium oxalate solution and it should develop at most a slight opalescence on the addition of silver nitrate solution. 

Silver nitrate solution is prepared by dissolving 85.20 g of pure AgN03 and diluting to 500.0 ml. 

A yellow to brown or black stain is produced,4 which is compared with a set of standard strips prepared under similar conditions. The chief difficulty encountered is to obtain a reliable and permanent set of standards especially is this the case with silver nitrate, the stains of which do not keep. The most satisfactory method5 of preparing such stains is to soak the filter paper in gum tragaeanth, dry it, soak it in silver nitrate solution, again dry it, expose to arsine under the requisite conditions and fix the stain by repeated soaking in very dilute ammonia and coating with paraffin. By the use of 66 per cent, silver nitrate solution, OT x 10-6 g, of As may be detected.6... 

Salts therefore, are prepared (1) from solutions of acids and bases by neutralization and separation by evaporation and crystallization (2) from solutions of two salts by precipitation where the solubility of the salt formed is slight (e.g., silver nitrate solution plus sodium chloride solution yields silver chloride precipitate [almost all as sulid], and sodium nitrate present in solution as sodium cations and nitrate anions [recoverable as sodium nitrate, solid by separation of silver chlondc and subsequent evaporation of the solution]) (3) from fusion of a basic oxide (or its suitable compound—sodium carbonate above) and an acidic oxide (or its suitable compound—ammonium phosphate), since ammonium and hydroxyl are volatilized as ammonia and water. Thus, sodium ammonium hydrogen phosphate... 

Extent of Salting.—In ordinary wines the chlorides present should not correspond with more than 1 gram of sodium chloride per litre. To ascertain if this limit has been exceeded a silver nitrate solution is prepared capable of precipitating this amount of chlorides from a given quantity of wine. 

Prepare the silver oxide by adding dilute sodium hydroxide solution gradually to a stirred 10 per cent aqueous silver nitrate solution - until precipitation is just complete. Wash the product thoroughly with distilled water. 

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