If two plates of Monel (70Ni-30Cu) are joined by a Cd screw and this assembly is
ID: 1010495 • Letter: I
Question
If two plates of Monel (70Ni-30Cu) are joined by a Cd screw and this assembly is placed in sea water: Monel and Cd will form a glass with H^+ ions from water Cd will corrode there will be no corrosion Monel (70Ni-30Cu) will corrode both will corrode If two plates of Ti are joined by a silver screw and this assembly is placed in sea water: Ti will corrode Ag will corrode there will be no corrosion both will corrode Ti-Ag will form a glass with H^+ ions in water Pure Co is more susceptible to corrosion than pure: Cu Zn Mg Na K CrExplanation / Answer
Solution:- All these are dependent on the standard reduction potentials. The metal with more negative value of standard reduction potential get's oxidized and does reduction of another metal or element.
If we take a look at the electrochemical series than standard reduction potential of Cd(-0.403 V) is more negative than Ni (-0.25 V) and Cu(+0.337 V). In corrosion, Metal get's oxidized. Since the standard reduction potential of Cd is greater than Ni and Cu, it's corrosion will take place. So, the correct choice would be second one, "Cd will corrode."
(3) Standard reduction potential value for Ti is negative where as it's positive for Ag. So, Ti will corrode.
(4) let's take a look at the standard reduction potential for all these metals.
Co+2 + 2e- -----> Co E0 = -0.277 V
Cu+2 + 2e- -------> Cu E0 = +0.337 V
Zn+2 + 2e- ------> Zn E0 = -0.76 V
Mg+2 + 2e- -----> Mg E0 = -2.37 V
Na+1 + 1e- --------> Na E0 = -2.71 V
K+1 + 1e- -------> K E0 = -2.9 V
Cr+3 + 3e- ------> Cr E0 = -0.74 V
pure Co would be more susceptible to corrosion than the pure metal that has less negative value of standard reduction potential than Co. From the potential values it is only Cu that has positive value means less negative than Co. So, the correct choice is Cu.