Textbook Problem 6N.23

[Madilyn Schindler 3E]

6N.23 (a) Suggest two metals that could be used for the cathodic protection of a titanium pipeline. (b) What factors other than relative positions in the electrochemical series need to be considered in practice? (c) Often copper piping is connected to iron pipes in household plumbing systems. What is a possible effect of the copper on the iron pipes?

Would someone mind explaining this problem, specifically (a) and (c)? Thanks!

[Emily Ding 1J]

In order to determine cathodic protection, or that Ti won't be oxidized/act as the anode, we need to find metals that have smaller reduction potentials. With a smaller reduction potential, this metal would act as the anode and get oxidized (so that our Ecell is still +) while Ti would be protected. Any metal works as long as it's below Ti in the electrochemical series, such as Al or Mg.

For part C, the reduction potentials for Cu+2 and Cu+ are 0.34 and 0.52 V respectively, while those of Fe+3 and Fe+2 are -0.04 and -0.44 V. In the case of matching these two metals up in a redox cell, we can see that Fe would act as the anode because its reduction potentials are much smaller and would result in a +Ecell, so Fe would be oxidized. So the effect of copper on iron pipes would be that the iron pipes would be oxidized/rust.