Silver Oxide

Silver (I) oxide is a chemical compound with the formula Ag 2 O. It is a fine black or dark brown powder used to prepare other silver compounds.

preparation

Silver(I) oxide is produced by reacting lithium hydroxide with a very dilute silver nitrate solution.

Silver oxide can be prepared by mixing an aqueous solution of silver nitrate and an alkali hydroxide. [7] [8] This reaction does not carry a sufficient amount of silver hydroxide because of the favorable energy for the following reaction:

2 AgOH → Ag 2 O + H 2 O ( p K = 2.875)

With suitably controlled conditions, this reaction can be used to prepare Ag2O powder with properties suitable for many uses, including as a fine-grained conductive paste filler.

Structure and Properties

Ag 2 O has linear, two-coordinate Ag centers attached to tetrahedral oxides. It is isostructural with Cu 2 O, It “dissolves” in solvents which degrade it. It is slightly soluble in water due to the formation of the ion Ag(OH) .-
2and possibly related hydrolysis products. [12] It is soluble in ammonia solutions, producing the active compound of Tollens’ reagent. A solution of Ag 2 O is readily attacked by acid :

Ag 2 O + 2 Hx → 2 AgX + H 2 O

where HX = HF, HCl, HBr, HI, or CF 3 COOH. It will also react with a solution of alkali chloride to precipitate silver chloride, leaving a solution of the corresponding alkali hydroxide. [12] [13]

Like many silver compounds, silver oxide is photosynthetic. It also decomposes at temperatures above 280 °C. 

Application

This oxide is used in silver-oxide batteries. In organic chemistry, silver oxide is used as a mild oxidizing agent. For example, it oxidizes aldehydes to carboxylic acids. Such reactions often work best when silver oxide is prepared from silver nitrate and alkali hydroxide .

Silver Oxide (Ag2O): Structure, Properties, Nomenclature and Uses

Silver oxide is an inorganic compound with the chemical formula Ag 2 O. The force that holds its atoms together is purely ionic in nature; Therefore, it consists of an ionic solid, where the ratio of the two Ag cations + electrostatic interactions with the O anion is 2- .The oxide ion, O 

2 , occurs as a result of the interaction of surface silver atoms with oxygen from the environment; In a similar way to iron and many other metals. A silver piece or jewelry, instead of turning red and breaking into rust, turns black, characteristic of silver oxide.

For example, in the image above you can see a Rusty Silver Cup. Note its black surface, although it still retains some decorative luster; This is the reason why rusty silver objects can be considered quite attractive even for decorative use.

The properties of silver oxide are such that they do not corrode, at first glance, the surface of the parent metal. It is formed at room temperature by simple contact with oxygen in the air; And even more interesting, it can decompose at high temperatures (above 200 ° C).This means that if the glass of the image was held, and the heat of an intense flame was applied, it would recover its silvery luster. Therefore, its formation is a thermodynamically reversible process.

Silver oxide has other properties as well and, beyond its simple Ag formula 2 OR, it encompasses a rich variety of complex structural organizations and solids. However, A.G. 2 or it is probably, next to Ag 2 O 3 , the most representative of silver oxides.

Structure of Silver Oxide

How is its structure? As mentioned in the beginning: it is an ionic solid. For this reason, it cannot contain covalent bonds Ag – O nor Ag = O in its structure; Since, if there were, the properties of this oxide would change drastically. It then has Ag ions + and O 2- in the ratio of 2:1 and experiences electrostatic attraction.

The structure of silver oxide is determined as a result of the way ionic forces settle in space + and O 2 – .

In the upper image, for example, you have a unit cell for a cubic crystalline system: Ag cations + silver are the blue sphere, and O 2- is the red sphere.If you count the number of shells, you will find that at first glance, there are nine silver blue and four red. However, only the fragments of the sphere contained within the cube are taken into account; Because of the different counts of the total areas, a 2:1 ratio must be met for Ag 2 O.

Repeating the structural unit of the AgO tetrahedron surrounds 4 to form four other Ag + , all-black solids (reducing the gaps or irregularities in these crystal arrangements).

Valencia’s numbers change with

Now ignoring the azo tetrahedron 4 but in line AgOAg (inspect the corner of the upper cube), it would be that the silver oxides are solids, from another point of view, arranged linearly of many ion layers ( however willing). This is all a result of the “molecular” geometry around Ag + .The above has been confirmed by numerous studies of its ionic structure.

Silver mainly works with valence +1, because after losing one electron its electronic configuration is [Kr] 4d 10 , which is very stable. Other valences, such as ag. 2+ and Ag 3+  They are less stable because they almost completely fill electrons from orbitals.

The Ag ion 3+ , however, is relatively less volatile than Ag 2+ . In fact, it can coexist in the company of AG + chemically enriching the composition.Its electronic configuration is [Kr] 4d 8 , with unpaired electrons in a way that gives it some stability.

In contrast to the linear geometries around Ag ions + , it is found that the Ag ions of 3+ are squarely flat. Therefore, a silver oxide with Ag ions will consist of 3+ layers composed of AgO classes 4 (not tetrahedra) connected electrostatically by AgOAg lines; Such is the case of Ag 4 O 4 or Ag 2 O Ag 2 O 3 with monoclinic structure.

physical and chemical properties

If you scratch the surface of the main image’s silver cup, you’ll find a solid one, which is not only black, but also has brown or gray tones (top image). The following are some of its physical and chemical properties, as explained by moments:

molecular weight

231,735 g/mol

appearance

Solid dark brown in powder form (note that despite being an ionic solid, it lacks a crystalline appearance). It is odorless and when mixed with water gives it a metallic taste.

density

7.14 g / ml.

Melting point

277-300 °C. Sure enough, it melts into solid silver; That is, it probably breaks down before forming the liquid oxide.

kps

1.52 10 -8 in water at 20 °C It is therefore a compound hardly soluble in water.

solubility

If you look carefully at the image of its structure, you will find that A.G. 2+ and O2- they almost do not disagree in size. As a result, only small molecules can penetrate the interior of the crystalline lattice, making it insoluble in almost all solvents; except those where it reacts, such as bases and acids.

covalent character

Although it has been repeatedly stated that silver oxide is an ionic compound, some properties, such as its low melting point, contradict this statement.

Of course, the idea of ​​covalent character does not break down what is explained for its structure, it would be enough to add it to the structure of Ag 2 or a model of spheres and bars to indicate covalent bonds.

In addition, tetrahedra and square plane a.g.o. Along with the 4 , AgOAg lines, they will be linked by covalent (or covalent ionic) bonds.Keeping this in mind, A.G. 2 or it will actually be a polymer. However, it is recommended to consider it as an ionic solid with a covalent character (the nature of which is still a challenge).

rot

First it was mentioned that its formation is thermodynamically reversible, so it absorbs heat to return to its metallic state. All this can be expressed by two chemical equations for such reactions:

where Q represents the heat in the equation. This explains why the fire that burns the surface of a rusty silver cup returns its dazzling luster.

Therefore, it is difficult to assume that Ag is 2O (L) since it will decompose immediately by heat; Unless, the pressure is too high to get a brownish black liquid.

Glossary

When the possibility of Ag ions was introduced 2+ and Ag 3+ the common and dominant Ag. The term ‘silver oxide’ appears to be insufficient to refer to + , Ag 2 O.

This is because the Ag ion + is more abundant than the others, so Ag is taken 2 or only as the oxide; Which isn’t quite right.

If you ag 2+ As practically no one has given their volatility, then only ions with values ​​+1 and +3 would exist; That is, Ag(I) and Ag(III).

Valencias I and III

Ag(I) being the least valence, it is named after adding the suffix -so to Argentum . So, A.G. 2 or it is: argentoso oxide or, according to systematic nomenclature, diplo monoxide.

If Ag(III) is completely ignored, it must have the traditional nomenclature: silver oxide instead of argentine oxide.

On the other hand, Ag(III) is suffixed to its name due to its greater valence. So, A.G. 2 O 3 is: silver oxide (2 Ag ions 3+ with three O 2- ). Also, according to the systematic nomenclature it will be named: Diplotrioxide.If the composition of Ag is observed 2 O 3 , it can be assumed that it is a product of oxidation by ozone, or 3 , instead of oxygen. Therefore, its covalent character should be high as it is a covalent compound with Ag-OOO-Ag or Ag-O bond. 3 -ag.

Systematic nomenclature for complex silver oxide

AgO, also written as Ag 4 O 4 or Ag 2 O Ag 2 O 3 , is silver oxide (I, III), because it has both the values ​​+1 and +3. According to the systematic nomenclature it will be named: tetraplate tetraoxide.

This nomenclature helps a lot when it comes to other stoichiometrically more complex silver oxides. For example, suppose there are two solids 2Ag 2 O Ag 2 O 3 and Ag 2 O g 3Ag 2 O 3 .The first one would have to be written in a more appropriate way: Ag 6 O 5 (counting and adding the atoms of Ag and O). Its name would then be Hexaplate Pentoxide. Note that this oxide has a silver composition less rich than Ag 2 O (6: 5) < 2:1).

When writing the second solid, it would be: Ag 8 O 10 . Its name would be octaplate dicooxide (with a 8:10 or 4:5 ratio). This hypothetical silver oxide would be “very oxidised”.

Applications

Studies exploring new and sophisticated uses of silver oxide are still being conducted today. Some of its uses are listed below:It dissolves in ammonia, ammonium nitrate and water to form Tollens’ reagent. This reagent is a useful tool in qualitative analysis within organic chemistry laboratories. This allows the presence of aldehydes in a sample to be determined, with a positive reaction occurring in the form of the formation of a “silver mirror” in the test tube.

Together with the metal zinc, it forms a primary battery of silver zinc-oxide. This is probably one of its most common and homelike uses.

-It acts as a gas purifier, for example absorbs CO 2 . When heated, it releases trapped gases and can be reused many times.Due to the antimicrobial properties of silver, its oxide is useful in bioanalysis and soil purification studies.

It is a mild oxidizing agent capable of oxidizing aldehydes to carboxylic acids. It is also used in the Hoffmann reaction (tertiary amine) and participates in other organic reactions, either as a reagent or a catalyst.