The Effects of Acid on different kinds of metal

Hi, Jake. Your school or town librarian should be able to help find books for you on interesting science projects and on acid attack on metal. I think that is the first step.

If your library trip doesn't pique your curiosity about some specific aspect of this that you'd like to address, maybe the teacher will let you change the project to something you would enjoy more? Enthusiasm is key to a worthwhile project -- you have to be interested in learning the results.

For a "routine" project, pick some dilute common acids hopefully available in your high school lab like hydrochloric, sulfuric, phosphoric, acetic, and nitric; and pick some common metals like steel, zinc, copper, and aluminum. Conduct tests under the supervision of the chemistry teacher or lab assistant. Obviously these acids can be hazardous and this part of the project must be done in the lab; unfortunately, you can't put the acid on display on project night, but you can certainly display the corroded metal.

Later you can flesh this out the subject by searching the internet for hits containing both the acid name and the metal name. Good luck!

Jake,

What Ted says makes sense. But YOU have to chose WHICH acid you want to write about.

Why? Because some acids attack some metals and others don't. And mixtures of acids can be very aggressive!

So start with, say, Hydrochloric (sometimes called Muriatic) or sulfuric.

Go to GOOGLE and try to get data on corrosion resistance of metals on the acid of your choice. OK?

And to prove to your teacher wotta good pupil you are, mention Aqua Regia (King of Waters) which dissolves gold. What is it? Look it up, Jake !

Hi, Brandy.

You didn't mention what grade your child is in, but a good starting point might be a high school chemistry text. It will explain in detail exactly what acids are, how they work, and why. Most acids quickly dissolve active, light, metals like aluminum, magnesium, and zinc by putting the metal into solution as an ion. They will act more slowly on iron (steel). Most acids will remove tarnish from more noble metals like copper, by dissolving the oxides into ions, while not having the power to oxidize and dissolve the metal itself. Most acids will have no effect on gold (aqua regia, a mixture of hydrochloric and nitric acid, being the exception). Nitric acid is an oxidizing acid (both an oxidizer and an acid) and its effects are stranger--it will dissolve metals like copper, which simple acids won't; but it will not dissolve aluminum, which simple acids will.

For younger students, I personally don't see value in rote memorization of the effects of various acids on various metals -- they haven't yet had chemistry so they will not gain any insight. What the younger students should be learning (in my opinion, but who am I) is the "method" of doing science experiments and projects. And this is about forming a hypothesis, distinguishing between observation, guesses, and conclusions, keeping a lab book and writing everything down, never erasing a single word, and how to do research. For me or anyone to simply respond that such & such an acid will do so & so to such & such a metal doesn't seem to me to get to the heart of the desired learning experience.

If a science project would benefit from input by people involved in metal finishing, our readers usually leap cheerfully to help, and you'll see hundreds of examples on these pages! But it isn't within our power to clarify a homework assignment, to make up for a poor selection of books in the school library, or to answer homework questions for millions of students around the world. Further, teachers are constantly imploring us to: "Just tell the students to do their own homework!"

Good luck.

Ted,

I couldn't agree with you more about the fact that kids try to take the easy way of finding answers. However, I have been to my local library for research questions only to find that the resources are out of date or do not go in depth enough. Then I was directed to go on line for answers. My son thought he hit a gold mine when he found all those responses and left them for me to read. I told him he had a wealth of info and to come read! He was looking for the effects of phosphoric acid on metals. His science project though stemmed from Coca-cola and the effects it had on various materials. So possibly the boy who originally asked the question might have had a broader topic. My son's teacher told him to look up acids and the effects they have on metals. That is how we got to this site.

Hi, David. Your question isn't tightly enough framed yet, because you haven't defined what you mean by "effect" (discolor? remove tarnish? corrode holes through? rust?) and you haven't yet specified the particular metals (for example, none of these will have any effect at all on gold).

But in general, vinegar or lemon juice will remove tarnish from copper, remove rust from steel, and corrode zinc. I don't know about orange juice.

Cut some post-1982 pennies into tiny pieces to expose the zinc core and leave them in these three materials for a week and see what effect you discover. Good luck.

Regards,

Hi, Sharon. Science is different than spelling or arithmetic; the object is not for your son to get the "right" answer like in spelling or arithmetic. The object is to learn how to form a hypothesis and to develop a test procedure that tends to confirm or disprove the hypothesis. You set up a test procedure, you honestly and accurately record your observations, and then you can try to understand and explain those observations. But your observations are non negotiable! You never ever change them even if the teacher and every other student got contrary results.

It is actually better if he doesn't know the results to expect, because then he won't be tempted to discount what he has seen, or repeat things until it turns out "right" due to some random event. If he feels pressure to get the "right" answer, he will be tempted to practice "junk science".

It really is important for him to understand the critical difference between things he has observed and his possible explanations for what he sees. Get a composition book .
and number the pages, give him a pen and have him record in ink the date and time and what he saw each time he removed the metals. If he starts writing, "there is some blue discoloration on the copper in the low pH . . ." let him continue because that would be a valid observation whether the other students got a blue discoloration or not. If you have a digital camera so that pictures are free, there is nothing wrong with taking pictures as the project proceeds.

If he starts writing "... because the copper metal is being converted to copper sulphate", stop him -- because he didn't observe that, he is presuming that. He should save explanations of why until after the experiment is complete.

If he learns to clearly differentiate between what he has actually observed vs. people's theories for why it happened, the project has been a huge success. If he learns to fudge his observations just a little bit so it's easier to arrive at the popular conclusions, the project was a disaster. Best of luck!

Regards,