Answer to Question #161564 in General Chemistry for mike

Question #161564

The black tarnish on silverware is silver sulfide. One way to clean the silverware is to wrap it in aluminium foil and submerge it (without air bubbles) in a solution of baking soda, NaHCO3. Depending on the degree of tarnishing, the silverware will be clean within one to five hours.

a) The half-reaction occurring on the surface of the silver is :

Ag2S(s)   +   2e-    →     2Ag(s)   +   S2-(aq)

Is this an oxidation or reduction process? Explain.

b) Explain why the aluminium foil is required and write a balanced equation for the overall reaction                                                                                                                                        

c) Give a reason why this method for cleaning silverware is better than polishing with a cloth.                                                                                                                                

Expert's answer

(i) reduction , because of gain of electron.

(ii) Aluminium has a stronger affinity for sulphur than silver, so in this reaction the aluminium simply displaces the silver from the silver sulphide compound, to free the silver metal and form the aluminium sulphide compound.

overall reaction is.

3Ag2S +2 Al "\\rightarrow" 6Ag + Al2S3

(iii) This silver sulphide tarnish can be quite easily removed using polishes that contain abrasives to rub off the silver sulphide, but these have the disadvantage of also removing small amounts of silver

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