Silver nitrate

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Silver nitrate (AgNO3) is a white solid silver salt that is very soluble in water. It is formed by dissolving silver in nitric acid.

Silver nitrate dissolved in water and with some nitric acid is the base of the electrolyte in silver cells.

WARNING!

Silver nitrate reacts with skin and nails and forms black spots that takes a long time to disappear. Longer contacts can be corrosive and cause blistering. Can cause blindness if splashed in the eye.

WARNING!

Dry silver nitrate reacts violently with magnesium and can be ignited by humidity.
YouTube video : Only a drop of water

WARNING!

Mixing silver nitrate with alcohol creates silver fulminate that is violently explosive when it dries.
YouTube video : Synthesis and explosive force.

Temperature stability

Silver nitrate can be reduced by heating, the breakdown is governed by the following equations:

2 AgNO3 = Ag2O + 2 NO2 + 1/2 O2    (1)
2 NO2 = 2 NO +O2                   (2)
2 AgNO3 = 2 Ag + 2 NO2 + O2        (3)
Ag2O = 2 Ag + 1/2 O2               (4)

Ag2O is quite unstable above 130° C so equation (1) and (4) will never reach equilibrium under normal atmospheric pressure. Qualitatively, decomposition is negligible in the solid state, but becomes appreciable 30-40° C above the melting point. Silver nitrate melts at 209.7 °C (409.5 °F; 482.8 K) so it starts to decompose around 250° C and totally decompose at 440° C.

Reduction back to silver

There are many methods to take silver nitrate back into silver, either directly or via an intermediate silver compound.

  • Reduction by formaldehyde or a number of ...
  • Reduction by sodium formate
  • Cementing with copper or other metal
  • Adding chloride ions to precitate silver chloride
  • Heating until decomposition

References

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