[Kaleyrvt]

a)    What metal might you fasten to the hull of an aluminum boat to give it
cathodic protection in the sea water?

Zinc would be a good choice in metal to fasten to the hull of an aluminum boat to give it cathodic protection in sea water since it is anodic,and oxidation occurs at the anodic side, and would be corroded itself, rather than the aluminum.

b)   Name two metals you would not use. Explain your choices.
   
Bronze and copper would not be a good selection of metals to use. This is due to the fact that they are far apart on the galvanic scale, and are cathodic themselves, thus would not be corroded first, but would allow the aluminum to be corroded.

Those are my answers--Am I even close??? Our text goes over what to use in a steel boat not an aluminum one--So I have no idea if this is correct. PLEASE *delete me*

[Yggdrasil]

Is zinc above or below aluminum in the activity series?  For a metal to provide cathodic protection, should it be above or below your metal in the activity series?

Also bronze might not be as good of a choice for your second answer because it is an alloy composed primarily of copper.  So you pretty much have the same answer as both of your examples.

[Kaleyrvt]

zinc is below aluminum in the activity series.....So not a good choice???Li+,K+ ,Ca2+ ,Na+ ,Mg2+ are all above Al3+....So it would be one of those then???

So then I could pick copper and gold for my second answer as they are below Al3+

[DevaDevil]

So then I could pick copper and gold for my second answer as they are below Al3+

For example, even though gold is not wanted for other reasons as well I imagine


In my opinion the question of cathodic protection of aluminium has no real practial value, sorry. Aluminium has an oxide layer in practice which protects it. But let's assume for the sake of argument that the hull is made of solid Aluminium:

Then you are right, you need a metal (not an ion!) with an even lower reduction potential (easier oxidised than Al)

[Kaleyrvt]

Thank you---so then is my first answer correct...A metal such a magnesium(whoch is above Al3+ would be good to give it cathodic protection? and the other 2 (gold and coopper) are bad choices???I am just not sure if you were changing my answer or if my final answers were ok???

[DevaDevil]

your final answers were ok in the line of the question as stated.

I was just mentioning practical factors in stead of theoretical ones. (like, of course no-one will use Gold as cathodic protection to prevent rust; not only would it not work, it would last only until it got stolen )

[Kaleyrvt]

That's what I thought, just wanted to be sure--- thanks a bunch