Silver Nitrate — Sodium Hydroxide Reagent

Note cautiously the characteristic odour of acetaldehyde which this solution possesses. Then with the solution carry out the following general tests for aldehydes described on p. 341 Test No. I (SchiflF s reagent). No. 3 (Action of sodium hydroxide). No. 4 (Reduction of ammoniacal silver nitrate). Finally perform the two special tests for acetaldehyde given on p. 344 (Nitroprusside test and the Iodoform reaction). 

It is preferable to use Tollen s ammoniacal silver nitrate reagent, which is prepared as follows Dissolve 3 g. of silver nitrate in 30 ml. of water (solution A) and 3 g. of sodium hydroxide in 30 ml. of water (solution B). When the reagent is requir, mix equal volumes (say, 1 ml.) of solutions A and JB in a clean test-tube, and add dilute ammonia solution drop by drop until the silver oxide is just dissolved. Great care must be taken in the preparation and use of this reagent, which must not be heated. Only a small volume should be prepared just before use, any residue washed down the sink with a large quantity of water, and the test-tubes rinsed with dilute nitric acid. 

Aromatic aldehydes react with the dimedone reagent (Section 111,70,2). All aromatic aldehydes (i) reduce ammoniacal silver nitrate solution and (ii) restore the colour of SchifiF s reagent many react with sodium bisulphite solution. They do not, in general, reduce Fehling s solution or Benedict s solution. Unlike aliphatic aldehydes, they usually undergo the Cannizzaro reaction (see Section IV,123) under the influence of sodium hydroxide solution. For full experimental details of the above tests, see under Ali-phalic Aldehydes, Section 111,70. They are easily oxidised by dilute alkaline permanganate solution at the ordinary temperature after removal of the manganese dioxide by sulphur dioxide or by sodium bisulphite, the acid can be obtained by acidification of the solution. 

Note Rhodamine B is a universal reagent that can be used on silica gel, talc, starch [5] and cellulose layers, just as on urea [1] or silver nitrate-impregnated [7] phases. Liquid paraffin-impregnated silica gel and RP layers are less suitable, since the background to the chromatographic zones is also intensely colored. It is often possible to increase the detection sensitivity by placing the plate in an atmosphere of ammonia after it has been sprayed or dipped, alternatively it can be oversprayed with sodium or potassium hydroxide solution. 

During preparation of an oxidising agent on a larger scale than described [1], addition of warm sodium hydroxide solution to warm ammoniacal silver nitrate with stirring caused immediate precipitation of black silver nitride which exploded [2], Similar incidents had been reported previously [3], including one where explosion appeared to be initiated by addition of Devarda s alloy (Al—Cu—Zn) [4], The explosive species separates at pH values above 12.9, only produced when alkali is added to ammoniacal silver solutions, or when silver oxide is dissolved with ammonia [5], The Sommer Market reagent mixture used to identify cellulose derivatives led to a severe explosion [6],... 

Transfer 150 ml of the silver nitrate reagent to each of two 250-ml glass-stoppered Erlenmeyer flasks. Place the flasks in a suitable ice bath until, die temperature of the contents Is 32°to 39.2 F (0° to 4°C). Add 7 to 9 drops of the mixed indicator to each flask and, if necessary, neutralize to a gray-green color with 0.02N sodium hydroxide if. acid or with 0.02N nitric acid if alkaline. Reserve one of the flasks for the blank and into the second flask pour 0 ml of propellant. Compare the color of the sample with that of the blank. A purple color in the sample solution indicates... 

Preparation of an Ammonia Solution of Silver. Dissolve 0.25 g of silver nitrate in 4 ml of water, and carefully, dropwise, add a concentrated ammonia solution until the precipitate dissolves (what iff its composition ). Add 9 ml of a 3% sodium hydroxide solution, and then more ammonia solution until the turbidity vanishes. Pour the solution into a measuring cylinder and add water up to a volume of 20 ml. Store the reagent in the dark. Why ... 

Miscellaneous class reactions. (Section 9.3.) Determine the effect of the following class reagents upon small portions of the original mixture (i) bromine in dichloro-methane solution (ii) potassium permanganate solution (iii) alcoholic silver nitrate solution (iv) 2,4-dinitrophenylhydrazine reagent (v) SchifFs reagent (vi) acetyl chloride (vii) benzoyl chloride (in the presence of aqueous sodium hydroxide) (viii) sodium (only if water is absent) (ix) iron(m) chloride solution and (x) bromine water. 

Ammonium, NH4 Sodium hydroxide Potassium tetraiodomercurate (Messier s reagent) Tannic acid-silver nitrate p-Nitrobenzene-diazonium chloride Evolution of ammonia gas upon heating Brown-yellow color or brown precipitate of mercury (II) amidoiodide high sensitivity all other metals (except Na and K) interfere Precipitate of black elemental silver, from neutral solution very sensitive Red-colored solution results in the presence of sodium hydroxide sensitivity, 0.7 pg of NH4+... 

The usual sugar-reagents do not serve to detect cyclitol spots (except those of inososes). Ammoniacal silver nitrate has been widely used, but the best results90 are obtained with separate solutions of silver nitrate in acetone and sodium hydroxide in ethanol.91 The Scherer test has been adapted for use on paper chromatograms,91 and other reagents are useful in certain instances.89-90... 

Chemically deposited films on frosted glass slides provide a more facile and reproducible approach to SERS substrates. One such approach [31], which has proven to be very successful, involves the initial preparation of Tollen s reagent. The reagent is prepared by adding about 10 drops of fresh 5% sodium hydroxide solution to 10 mL of 2 to 3% silver nitrate solution, whereupon a dark-brown AgOH precipitate is formed. This step is followed by the dropwise addition of concentrated NH4OH, at which point the... 

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