Cementation and Prevention of it by Deposition from the Complex Salt Solutions

1 Cementation and Prevention of it by Deposition from the Complex Salt Solutions 

If zinc is immersed in a copper sulfate solution, the reaction 

In a cyanide-containing bath, the copper potential is sufficiently negative so cementation does not occur and copper can be successfully deposited onto zinc. This is due to the fact that the cyanide complexes of copper are very strong so the potential of copper in such a solution is much more negative than in simple salt solutions. On the other hand, the zinc cyanide complex is relatively weak and the potentials of two metals become comparable so an external power supply is required to deposit copper on the zinc from cyanide. 

---