Compounds of Ag

The initial compound to obtain practically any other compound of silver is AgNO₃ that, in turn, is produced by dissolution of metallic silver in НNO₃.

Compounds Ag(I). The brown precipitate of silver oxide is formed at the action of alkalis on solutions of Ag(I):

2AgNO₃ + 2NаOН = Ag₂O + Н₂О + 2NаNO₃

AgOH exists in very diluted solutions, otherwise it decomposes.

Ag₂О is slightly soluble in water (~ 0,02 g/L at 20°). It reacts reversibly with water that is attended by the relatively strong base AgOH formation:

1/2Ag₂О + 1/2Н₂О AgОН Ag⁺ + ОН^-

The values of equilibrium constants К₁ and К₂ are 1,8×10^-6 і 2×10^-2, respectively. Therefore, saturated solutions of Ag₂O have a pH more than 7.

Ag₂О has predominately basic properties. It reacts with strong acids:

Ag₂О + 2HNO₃ = 2AgNO₃ + H₂О,

though it can be dissolved in concentrated solutions of alkalis forming dihydroxoargentate anion:

Ag₂О + H₂О + 2NaOH Na[Ag(OH)₂]

It can be decomposed at 160 ^oC:

2Ag₂О 4Ag + О₂

Salts. Soluble salts of Ag(I) with acid residues of strong acids don’t hydrolyse (AgNO₃, AgClO₄ etc.) since AgОН is a relatively strong base.

The solubility of silver halides is decreased in the series AgF to AgI. Insoluble halides AgCl (white), AgBr (yellowish), AgI (yellow) can be obtained by double replacement reactions:

AgNO₃ + KCl = AgCl↓ + KNO₃

SP in this series is also decreased gradually: AgCl 1,6×10^-10, AgBr - 8×10^-13, AgI -1,5×10^-16.

Ammonia forms with Ag(I) the cationic complex [Ag(NH₃)₂]⁺_. The dissolution of slightly soluble AgCl causes donor-acceptor interaction with NH₃:

AgCl↓ + 2NH₃ =[Ag(NH₃)₂]Cl

This reaction is reversible and the equilibrium is shifted to the formation of complex at the conditions of excess of ammonia. The equilibrium of the reaction in case of other halides is gradiually displaced to the reverse direction and AgI virtually inactive to NH₃.

Complexes. Coordination compounds of Ag(I) (Tollens' reagent) with ammonia can be reduced by aldehydes, glucose or some other reducing agents. A “silver mirror” forms in a clean glass reaction vessel. This feature is used as a test for aldehydes, which are oxidized to carboxylic acids.

2[Ag(NH₃)₂]Cl + R-COH + H₂O = 2Ag↓ + RCOOH + 2NH₄Cl + 2NH₃

This reaction is applied worldwide to produce mirrors and as a qualitative test on aldehydes.

The most stable complexes of Ag(I) are coordination compounds with thiosulfate anion. Therefore, all halides of silver are soluble in Na₂S₂O₃:

AgBr + 2Na₂S₂O₃ = Na₃[Ag(S₂O₃)₂] + NaBr

This reaction is used in black-and-white photography to remove AgBr after development (fixing solution). Ag(I) forms coordination compounds with alkynes and alkenes (for instance Ag-C≡C-Ag) alkyl and aryl derivatives of phosphines.

Compounds of Ag(II) and Ag(III). Many compounds of Ag(ІІ) are known but they are very unstable:

Ag + F₂ = AgF₂

Ag₂O + (NH₄)₂S₂O₈ + H₂O = 2AgO + (NH₄)₂SO₄ + H₂SO₄

AgO is a very strong oxidant:

4AgO + 2H₂SO₄ = 2Ag₂SO₄ + O₂ + 2H₂O

Ag₂O₃. It can be obtained by the anode electrodeposition of Ag(І) in alkali solutions.

Fluorine can oxidize halides of silver and fluorocomplexes can be obtained:

KCl + AgCl + 2F₂ = K[AgF₄] + Cl₂

Дата добавления: 2015-07-25