There is a peice of a copper wire in an aqueous solution. Upon closer expection, you realize the copper has a hard, metallic, substance coating it. Propose what might have happened. Include an example of a possible chemical reaction.
It sounds like the copper was placed in an solution of an ionic compound with a metal less reactive than copper. A displacement reaction occurs, the copper replaces the metal in the solution, and the other metal forms an insoluble precipitate around the copper.
A popular demonstration of this exact type of reaction is to place copper in a Silver Nitrate solution. 2AgNO3(aq) + Cu(s) ------>Cu(NO3)2(aq) + 2Ag(s) The Silver precipitates out slowly forming flakes around the Copper and the solution turns blue as it is now a Copper (II) Nitrate solution. I did this in High School.