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 lose electron ,oxidized, reducing agent.
O 0__-2 gain electrons, reduced, oxidizing agent.
2Al+3Ag2S+6H2O→6Ag+2Al(OH)3+3H2S0
Al 0_+3 lose electron ,oxidized, reducing agent.
Ag 1__0 gain electron ,reduced, oxidizing agent. +1 -2 1 3

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 AgCl:[3]
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.

5. 1. Change the internal origination of the metal
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.
Rust Protection

6. 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
3Ag+4HNO3=3AgNO3+NO↑+ 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.