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Question

What is the chemical formula for corrosion in copper and silver?


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Solution

Corrosion

  • Corrosion is a natural process that converts a refined metal to a more chemically stable state, such as oxide, hydroxide, or sulfide.
  • For example, when iron rusts, it loses its toughness, and the rusty iron crumbles readily.

Corrosion in copper

  • When copper metal is exposed to the environment, it combines with oxygen in the air to generate copper (I) oxide Cu2O, which appears red.
  • The reaction is as follows:

2Cus+12O2gCu2Os

  • Cu2O is oxidized further to produce black-colored copper (II) oxide CuO.
  • The reaction is as follows:

Cu2Os+12O2g2CuOs

  • CuO interacts with carbon dioxide CO2, sulfur trioxide SO3and water H2O in the environment to generate blue Cu2(OH)2(s) (Malachite) and green Cu4SO4(OH)6s (Brochantite).
  • This is why copper is turning bluish-green in color.

Corrosion in silver

  • Silver becomes silver sulfide (Ag2S) when it reacts with sulfur and sulfur compounds in the air.
  • Exposed silver interacts with Hydrogen Sulfide H2S in the atmosphere to generate Ag2S with the hydrogen gas H2.
  • The reaction is as follows:

2Ags+H2Sg+12O2gAg2Ss+H2g


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