SILVER TARNISH

1
SILVER TARNISH

• A Redox Reaction

2
overview

• Tarnish, which appears as black or brown streaks
  and patches on silver ware, is silver sulfide, a
  compound formed when silver interacts with sulfur
  in the air.

3
chemical equation

• 4 Ag O2 2 H2S ? 2 Ag2S 2 H2O
• Ag 0--1 lose electron ,oxidized, reducing agent.
• O 0__-2 gain electrons, reduced, oxidizing agent.
• 2Al3Ag2S6H2O?6Ag2Al(OH)33H2S0
• Al 0_3 lose electron ,oxidized, reducing agent.
• Ag 1__0 gain electron ,reduced, oxidizing agent.

0
1
-2
0
0
1
3
0
4
Other equation about silver

• In one of the most famous reactions in chemistry,
  addition of colorless aqueous silver nitrate to
  an equally colorless solution of sodium chloride
  produces an opaque white precipitate of AgCl3
• Ag(aq) Cl-(aq) ? AgCl(s)
• This conversion is a common test for the presence
  of chloride in solution. Due to its
  conspicuousness it is easily used in titration.

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Rust Protection

• 1. Change the internal origination of the metal.
  Like adding chromium, nickel to common steel can
  make stainless steel
• 2. Cover mulch on the surface of metal.
• 3. Dispose with corrosive.
• 4. Connect metal with reactive metal, when
  electrochemical corrosion happens, the reactive
  metals go through oxidizing reaction and prevent
  metal from corrosion
• 5. Connect metal with negative electrode, and
  then connect a conductive inert material with
  positive electrode.

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reaction between silver and acid

• sequence of simple metal activity
• Cs? Rb? K?Ba ? Ca? Na ?Mg ?Mn? Zn? Cr ?Fe ?Co
  ?Ni? (H2)? Cu? Hg ?Ag? Rh ?Pd ?Pt ?Au
• 3Ag4HNO33AgNO3NO? 2H2O
• 2Ag 2H2SO4 (concentrated)Ag2SO4 SO2?
  2H2O

7
factors affecting silver tarnish

• It is recognized that more pure the silver is,
  the easier it is eroded.
• The silver often is alloy with copper or other
  metals. Their electric potential is different,
  under certain conditions it will act like a
  reaction occurs inside the battery and eroded
  copper and also silver.
• For other factors, such as the concentrate of
  sulfuret and radiations such as ultraviolet
  affect the tarnish.