Silver mirrors, deposition

Silver ion, Ag, oxidizes aldehydes selectively in a convenient functional-group test for aldehydes. The Tollens test involves adding a solution of silver-ammonia complex (the Tollens reagent) to the unknown compound. If an aldehyde is present, its oxidation reduces silver ion to metallic silver in the form of a black suspension or a silver mirror deposited on the inside of the container. Simple hydrocarbons, ethers, ketones, and even alcohols do not react with the Tollens reagent. 

Some carbohydrates give a silver mirror deposit with ammoniacal silver nitrate solution as aldehydes do. What does this tell you about the structure of these carbohydrates ... 

Tollens reagent An ammoniacal solution of silver oxide which is used as a lest for aldehydes, which, unlike ketones, cause the deposition of a silver mirror. 

Readions. — i. Adda few chops of the acid solution or solution of the calcium salt to a few c.c. of ammonia-silver nitrate and warm in hot water. A silver mirror is deposited. 

Although it is obviously of no practical synthetic significance, mention may be made of Linnemann e observation1087 that sealing propylene oxide in the dark for 4 years in the presence of silver oxide caused deposition of a silver mirrOr and formation of silver acetate (Eq. 430). Formio arid underwent oomplete oxidation to carbon dioxide and water. 

It has been known for some time that silver(I) porphyrins are generally unstable toward disproportionation to the silver(II) complex, sometimes with deposition of a silver mirror.551... 

AgN03, white precipitate—Ag2C4H406, soluble in HN03, and ammonia. Precipitate dissolved in minimum quantity of ammonia, with addition of crystal of AgN03, deposits silver mirror on gently heating. 

Tollen s test The reagent should be freshly prepared by mixing two solutions (A and B). Solution A is a 10% aqueous AgNOs solution and solution B is a 10% aqueous NaOH solution. When the test is required, 1 ml of solution A and 1 ml of solution B are mixed, and the silver oxide thus formed is dissolved by dropwise addition of 10% aqueous NH4OH. To the clear solution, 10 drops of the compound to be tested are added. A silver mirror is indicative of the presence of an aldehyde. The reagent mixture (A + B) is to be prepared immediately prior to use otherwise, explosive silver fulminate will form. The silver mirror is usually deposited on the walls of the test tube either immediately or after a short warming period in a hot water bath. This is to be disposed of immediately with diluted HN03 (detection limit, 50 mg compounds tested, Q to C6). 

A test for aldehydes. The Tollens reagent is a silver-ammonia complex Ag(NH3)2 OH]. Tollens reagent oxidizes an aldehyde to a carboxylate salt and deposits a silver mirror on the inside of a glass container, (p. 862)... 

The system which is the nearest approximation to an ideally flat surface, from which reflection of light is exclusively mirror reflection, is the surface of a silver mirror or of mercury. For that reason, reflection and structural characteristics of a silver mirror surface were firstly examined in order to define the reference standard for the comparison of reflection and structural characteristics of different metal surfaces.7,8 Silver mirror surface is obtained by chemical deposition of silver onto a glass by the silver mirror reaction. 

Automatic and quantitative microscopes tend to give erroneous results for transparent particles. To overcome this problem Amor and Block [49] a silver staining technique to make the particles opaque. The particles are dry-mounted on to a thin film of tacky colloidon on a microscope slide. Silver is then deposited from solution using the silver mirror reaction. Preliminary sensitizing the crystalline surface ensures that much more silver is deposited on the particles than on the colloidon. A method of staining particles in aqueous solution prior to deposition on a membrane filter for analysis is also given. 

Before the advent of nmr and ir spectroscopy the chemist was often called upon to identify aldehydes and ketones by purely chemical means. Aldehydes can be distinguished chemically from ketones by their ease of oxidation to carboxylic acids. The oxidizing agent, an ammoniacal solution of silver nitrate, Tollens reagent, is reduced to metallic silver, which is deposited on the inside of a test tube as a silver mirror. 

Tollens Test. Follow the procedure on page 311, Chapter 30. A positive test, deposition of a silver mirror, is given by most aldehydes, but not by ketones. 

Tollen s reagent, a solution of silver nitrate in ammonia, oxidises aldehydes to carboxylic acids, and the silver ions are reduced to a deposit of silver metal which often collects as a thin silver mirror on the inside of the test tube ... 

If the remaining liquids are tested for a reducing agent with ammoniacal silver nitrate solution, the aldehyde should give a deposit of a silver mirror on the inside of the test tube the other, the ketone, gives no deposit. 

A few mL of 0.1 mol/L AgN03 solution are placed in the flask, w hich must be completely free of grease. Aqueous aiiimoiua is added until the white precipitate of Ag2() formed initially just rcdissolves. A large dash of saturated hydrazinium sulfate solution is added the flask is swirled rapidly and at the same time heated a little in the gas flame. The silver mirror is deposited on the inner wall of the flask (colored figure 4). 

Tollens reagent reacts with some aldehydes in cold conditions and some aldehydes in hot conditions. Metallic silver, produced in the reaction, is deposited on the walls of the vessel (silver mirror) or it precipitates. This reaction is used to detect the presence of an aldehyde or to distinguish between aldehydes and ketones. 

The silver precipitate produced by the Tollens reaction is deposited on glass. Silver mirrors are made In a similar process. 

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