Silver(I,III) oxide

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Silver(I,III) oxide
Identifiers
CAS number 1301-96-8 YesY
Properties
Molecular formula AgO

Ag2O.Ag2O3

Molar mass 123.87 g/mol
Appearance grey-black powder
diamagnetic
Density 7.48 g/cm3
Melting point >100 °C, decomposition
Solubility in water .0027 g/100 mL
Solubility soluble in alkalis
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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Infobox references

Silver(I,III) oxide is the inorganic compound with the formula Ag4O4. It is a component of silver oxide-zinc alkaline batteries. It can be prepared by the slow addition of a silver(I) salt to a persulfate solution e.g. AgNO3 to a Na2S2O8 solution.[1] It adopts an unusual structure, being a mixed-valence compound.[2] It is a dark brown solid that decomposes with evolution of O2 in water. It dissolves in concentrated nitric acid to give brown solutions containing the Ag2+ ion.[3]

Structure[edit]

Although its empirical formula, AgO, suggests that silver is in the +2 oxidation state in this compound, AgO is in fact diamagnetic. X-ray diffraction studies show that the silver atoms adopt two different coordination environments, one having two collinear oxide neighbours and the other four coplanar oxide neighbours.[1] AgO is therefore formulated as AgIAgIIIO2[4] or Ag2O·Ag2O3. It is being a 1:1 molar mixture of silver(I) oxide, Ag2O, and silver(III) oxide, Ag2O3. It has previously been called silver peroxide, which is incorrect since does not contain the peroxide ion, O22-.

Preparation[edit]

US patent 4003757 (Lux and Chobanov) describes one method for preparing this oxide (then called Ag(II)-oxide) in a form suitable for batteries and gives the following example:

In 1.5 liters of aqueous solution containing 150 grams of sodium hydroxide, 65 grams of silver powder are suspended with continuous stirring. The silver powder has a density of approximately 1.6 grams per cubic centimeter. Its grain size distribution is: 52% under 10 microns; 33% 10 microns to 30 microns, 15% above 30 microns.

The liquid is then heated to about 85° C. Upon reaching this temperature, a total of 200 grams of potassium peroxidisulfate (K2 S2 O8) in portions of about 40 grams each is added at intervals of, for example, 1 hour. After addition of the final portion of oxidant, stirring is continued for 3 hours. The product is then filtered, washed to free it of alkali substances, dried at a temperature of approximately 80° C and reduced to particle form.

The foregoing yields approximately 73 grams of silver-(I,III)-oxide with more than 95% content of pure silver-(I,III)-oxide. The silver oxide produced is characterized by high thermodynamic stability, low internal discharge and consequent long shelf life. The rate of gas evolution of there products in 18% NaOH is below 1 microliter per gram-hour at room temperature. This stability is attributable to the fact that the process embodying the invention produces single cyrstals of exceptionally regular shape and monoclinic form.


References[edit]

  1. ^ a b Wells A.F. (1984) Structural Inorganic Chemistry 5th edition Oxford Science Publications ISBN 0-19-855370-6
  2. ^ David Tudela "Silver(II) Oxide or Silver(I,III) Oxide?" J. Chem. Educ., 2008, volume 85, p 863. doi: 10.1021/ed085p863
  3. ^ Peter Fischer, Martin Jansen "Electrochemical Syntheses of Binary Silver Oxides" 1995, vol. 30, pp. 50–55. doi:10.1002/9780470132616.ch11
  4. ^ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 0080379419.  p. 1181.