Science Buddies: "Ask an Expert"

My project is the the effect of the material of hardware on corrosion through acid rain. I bought four different types of metals/alloys in the form of either a nail or a screw (some of the metals/alloys aren't used to make nails so I had to buy screws or vice versa). For my project I'm going to make a solution of vinegar water, dip the hardware in the solution, and then leave the hardware out. After it is dry (6 hours), I'm going to take the mass of the nails and repeat 4 or 5 times.

I have 2 problems. I'm not sure whether this is the process of oxidation or corrosion, which is actually quite a big problem because it's the main concept of my experiment. I've had it explained to me by a cousin of mine and he said that oxidation is a broad topic and corrosion is a type of oxidation which is always destructive. Is this accurate? So my title could say oxidation, but corrosion is more specific? Just to clarify, I'm NOT using iron as a metal, which would change things, correct? Then everything would be corrosion except for that which would be rust, which IS a type of oxidation but NOT a type of corrosion?

Second, should the hardware be gaining or loosing mass? I'm almost sure it would be losing mass, but if for some reason the answer to my above question is oxidation and not corrosion, then I have no idea what it would be doing.

I was previously having a really difficult time understanding this because I was under the impression that oxidation and rust were synonymous, but now I know that rust just refers to when iron is oxidized (iron oxide) and that there are different types of oxidation. Basically, I think I understand everything now but I just want to make sure that everything I think is actually correct.

Please answer, I have less than a week until my project is due!

And thanks in advance!

reignbough - There is a tricky conundrum here. All oxidation can be considered corrosion, but not all corrosion is, in fact, oxidation. I think you should do more research on oxidation (oxygen is involved) and it's cousin corrosion (something is combining and degrading your base material, but it is not oxygen). Once you have this well understood, I think you will have a much easier task of understanding how to prepare your experiment, what you will be looking for in your measurement and analysis, and how you present your conclusion.

Rick Marz

rmarz wrote:reignbough - There is a tricky conundrum here. All oxidation can be considered corrosion, but not all corrosion is, in fact, oxidation. I think you should do more research on oxidation (oxygen is involved) and it's cousin corrosion (something is combining and degrading your base material, but it is not oxygen). Once you have this well understood, I think you will have a much easier task of understanding how to prepare your experiment, what you will be looking for in your measurement and analysis, and how you present your conclusion.

Rick Marz

I have done some more research and now it makes more sense to me. So my previous statement just needs to be reversed: oxidation is a type of corrosion, not the other way around. My experiment would have two types of corrosion: uniform corrosion because of the acid, and oxidation because of the oxygen. What I'm still not understanding is whether this would be a mass gain or mass loss. I can't find any credible answers to this: all I find are yahoo answer links that only deal with rusting, not corrosion in general, and even with this, half the people say mass gain and half say mass loss. Do you have any credible links that would help me research this answer or do you have any background information that could help me?

Thanks.

reignbough - In corrosion or oxidation, mass can increase or decrease depending on what happened to the product of the chemical reaction. For example, suppose you took an iron spike weighing 1 ounce, and subjected it to an environment that caused heavy oxidation (or rust) to form. If you weighed the spike, it would have increased mass (over 1 ounce) due to the quantity of oxygen that is now surrounding the spike in the form of iron oxide. If you carefully removed the oxidation with a wire brush the remaining iron spike would be less than 1 ounce because you removed some of the iron atoms that are now part of the iron oxide. Similar situations apply to the process of corrosion. Where did the product of corrosion or oxidation go? The attached link discusses an interesting application for what is called a 'sacrificial anode' a material that will protect items from the process of galvanic corrosion by introducing a more active material that will sacrifice itself to protect a pipeline, underground tank, ship hull or similar metal object.


http://chemwiki.ucdavis.edu/Analytical_ ... cial_Anode

Rick Marz