Complex silver ammonia

Qualitative. The classic method for the quaUtative determination of silver ia solution is precipitation as silver chloride with dilute nitric acid and chloride ion. The silver chloride can be differentiated from lead or mercurous chlorides, which also may precipitate, by the fact that lead chloride is soluble ia hot water but not ia ammonium hydroxide, whereas mercurous chloride turns black ia ammonium hydroxide. Silver chloride dissolves ia ammonium hydroxide because of the formation of soluble silver—ammonia complexes. A number of selective spot tests (24) iaclude reactions with /)-dimethy1amino-henz1idenerhodanine, ceric ammonium nitrate, or bromopyrogaHol red [16574-43-9]. Silver is detected by x-ray fluorescence and arc-emission spectrometry. Two sensitive arc-emission lines for silver occur at 328.1 and 338.3 nm. 

In a linear complex, the coordination number is 2, corresponding to one group on each side of the central atom. The silver-ammonia complex, which generally forms when a very slightly soluble silver salt such as silver chloride dissolves in aqueous ammonia, is an example, as shown in Figure 22-6. Another example of a linear com-... 

Metal cations in aqueous solution often form chemical bonds to anions or neutral molecules that have lone pairs of electrons. A silver cation, for example, can associate with two ammonia molecules to form a silver-ammonia complex ... 

Notice that square brackets are used in a new way for the silver-ammonia complex in the chemical reaction. Chemists use square brackets to identify a complex ion such as [Ag (NH3)2, because the species involved in... 

The stoichiometiy of a metal complex is described by its chemical formula. For example, each cation of the silver-ammonia complex contains one Ag cation bound to two neutral NH3 ligands and carries a net charge of -i-l, as shown in Figure 18-11. The formula of a complex ion is enclosed in square brackets, as in [ Ag (NH3)2. The... 

Because the two equilibrium constant expressions have similar magnitudes, a solution of the silver-ammonia complex generally has a significant concentration of each of the species that participate in the equilibria. The details of such calculations are beyond the scope of general chemistry. When the solution contains a large excess of ligand, however, each step in the complexation process proceeds nearly to completion. Under these conditions we can apply the standard seven-step approach to a single expression that describes the formation reaction of the complete complex. 

Although 6 Is most prevalent, a coordination number of 4 Is also common, and several important complexes have a coordination number of 2. In addition, a few complexes display coordination numbers of 3, 5, and 7. Examples of coordination number 2 include the silver-ammonia complex and the gold-cyanide complex, both described in Chapter 18. To minimize ligand-ligand repulsions, a complex with a coordination number of 2 is invariably linear, as Figure 20-6 shows. 

E—Aqueous ammonia contains NH3. The reaction produces the silver-ammonia complex, [Ag(NH3)2]+. 

The silver chloride (AgCl) is dissolved as the stable silver-ammonia-complex ion [Ag(NH3) 2+] is formed. Meanwhile, the mercury II chloride (HgCl2) is undergoing oxidation and reduction at the same time Mercury metal (Hg) and mercury II amidochloride (HgNH2Cl) are formed and appear, respectively, black and gray in color ... 

The mercury substances are filtered, and silver ions (Ag+) are detected in the filtrate by adding hydrochloric acid (HC1), which releases the silver ions from the silver-ammonia-complex ion [Ag(NH3) 2+], allowing the silver ions to combine with chloride ions (Cl") to form silver chloride precipitate (AgCl) ... 

Both the ions of Ag+ and Cif are easily complexed by ammonia (amine) and the corresponding complexes are very stable [204]. In the system of silver-ammonia complex ions the oxidation-reduction standard electrode potential of silver is expressed by... 

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. 

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)... 

A test for reducing sugars, employing the same silver-ammonia complex used as a test for aldehydes. A positive test gives a silver precipitate, often in the form of a silver mirror. Tollens reagent is basic, and it promotes enediol rearrangements that interconvert ketoses and aldoses. Therefore, both aldoses and ketoses give positive Tollens tests if they are in their hemiacetal forms, in equilibrium with open-chain carbonyl structures, (p. 1118)... 

The silver ammonia complex, Ag(NH8)2, is sufficiently stable for ammonium hydroxide to dissolve precipitated silver chloride by re-ducing the concentration of silver ion, [Ag+], below the value required for precipitation by the solubility product of AgCl. A satisfactory test for silver ion is the formation with chloride ion of a precipitate which is soluble in ammonium hydroxide. 

Ores of silver native silver, argentite, cerargyrite (horn silver). Metallurgy of silver cyanide process, amalgamation process, Parkes process. O mpoimds of silver silver oxide, silver chloride, silver bromide, silver iodide, silver ammonia complex, silver cyanide complex, silver thiosulfate complex, silver nitrate. 

Tollen s test. Glucose and other aldoses are oxidized by an aqueous solution of a silver-ammonia complex. What are the reaction products ... 

EXAMPLE 7-6 Calculate the solubility of silver iodide in 0.01 M ammonia, if the solubility product of silver iodide is 9 x 10 and the logarithms of the successive formation constants of the silver-ammonia complexes are 3.2 and 3.8. 

When silver ions are dissolved in an aqueous ammonia solution, doubly coordinated silver-ammonia complexes, shown in Figure 16.13, form in two stepwise reactions ... 

A closely related second method to achieve an even denser metallic layer involves the introduction of tin ions instead of silver followed by a spray of water-based silver-ammonia complex, freshly mixed with reducer. The tin catalyzes the deposition of silver, resulting in the formation of colloidal metallic silver. Upon drying, a very regular, shiny metallic silver layer with a thickness ranging from 10 to 600 atoms is produced as indicated formally below ... 

The unknown is fairly soluble in water and produces a silver mirror when treated with the silver ammonia complex. A red precipitate appears when it is treated with the Benedict s reagent. Which of the compounds is the correct structure for the unknown Explain your reasoning. 

III The aldehyde D is oxidised to an acid by the silver/ammonia complex ions. 

Aldehydes selectively react in a solution of silver-ammonia complex called Tollen s reagent. A sample reaction is given below. 

One of the fundamental problems of using chemistry such as this one, is the thermodynamic instability of the solution. In other words, if both the silver-ammonia complex and the reducing agent are present in solution the reaction may proceed irreversibly. In practical terms this means that the mixed solution is unstable and the details of the procedures do matter. In fact, one of the roles of the ammonia is to stabilize the silver ions, as unprotected silver nitrate solutions will be reduced by formaldehyde spontaneously under a wide range of conditions. 

Aldehydes are also oxidized to carboxylic acids by silver ion. One common laboratory procedure uses Tollens reagent, prepared by dissolving AgN03 in water, adding sodium hydroxide to precipitate silver ion as AggO, and then adding aqueous ammonia to redissolve silver ion as the silver-ammonia complex ion ... 

A laboratory test that distinguishes aldehydes from ketones takes advantage of their different ease of oxidation. In the Tollens silver mirror test, the silver-ammonia complex ion is reduced by aldehydes (but not by ketones) to metallic silver. The equation for the reaction may be written as follows ... 

Setting Up In a 10-mL Erlenmeyer flask, prepare a solution of silver ammonia complex from 2.5 mL of 0.1 A/f silver nitrate solution by adding ammonium hydroxide solution dropwise. Brown silver oxide forms first add just enough ammonium hydroxide to dissolve the silver oxide. Dilute the solution by adding 1.5 mL of water. 

Dilute the remaining silver ammonia complex test solution with water and flush it down the drain with water. Destroy all solid silver acetylide salt by treatment with hydrochloric acid. Collect the silver chloride and put it in a container for heavy metals, and then flush the filtrate down the drain. 

Another method for distinguishing between aldehydes and ketones is Tollens s test. A positive test indicates the presence of an aldehyde function, whereas no reaction occurs with ketones. Tollens s reagent consists of silver-ammonia complex, Ag(NH3)2, in an ammonia solution. This reagent oxidizes both aliphatic and aromatic aldehydes to the corresponding carboxylic acids silver ion is reduced to elemental silver, which is deposited as a silver mirror on the glass wall of a clean test tube. Thus, the formation of the silver mirror or of a precipitate is considered a positive test. Equation 25.12 shows the reaction that occurs. 

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