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Why does copper sulphate induce a kind of rust on a nail?

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Q. Hello.

I'm doing a project and I was wondering if anybody could tell me what the chemical for copper sulphate is, and why it (induces) rust so quickly, if any one knows the answers to these questions, please feel free to tell me here! :) Thank you.

Oh yes, this is semi-urgent so if you have an answer please tell me now. ;)

Courtney S deleted
- Trenton Ontario, Canada


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A. Hi, Courtney. Actually, the chemical for copper sulfateamazoninfo is usually, it is found as blue copper sulphate pentahydrate crystals (sometimes available in pool supply stores), and the chemical formula for that is CuSO4.5H2O. Those crystals can be dissolved in water and then it will make a blue solution of copper sulphate.

To my knowledge it does not cause a nail to rust, but copper metal does plate out onto the nail, and copper is sort of an orange-ish color that could perhaps be mistaken for rust. If you tell us what grade you are in we can try a grade-appropriate answer (by which I mean that if you are a high school senior, we do no favor to your education by talking babytalk; but there may be little point in esoteric chemistry terminology if you are in grade school, years away from studying chemistry nomenclature). Good luck!

pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


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Copper sulphate rusts really quickly because when oxygen is interfered sulfate it causes a chemical reaction. This chemical reaction causes anything to rust in minutes or even hours. Copper's sulphate chemical properties are that it reacts to oxygen and once the oxygen reacts it eats away the copper sulphate metal.

Sincerely,

Yevgeny Shnaper
- Toronto, Ontario, Canada


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Congratulations to Mr Mooney on his patience when answering these questions - I'd just like to add a less misleading answer to this question than that provided by Mr Shnaper.

A. The "rust" on the nail is probably a powdery coating of metallic copper (which looks a rusty reddish brown), the copper ions come out of solution, oxidising the metallic iron atoms to make them into iron ions which dissolve. The "oxidising" here means a transfer of electrons (the copper ions are "reduced" at the same time). Copper II sulphate doesn't react too easily with oxygen as stated, it's already so "oxidised" that it can in fact "oxidise" the iron metal.
I use this resource occasionally to clear up queries on metal finishing chemistry and generally trust what I read here, so I guess most people would, and hate to think of them being so misled.

Ray Hicks
- Cambridge, U.K.



What do electrons have to do with it?

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Q. I'm a student in eighth grade working on a school science project in immersion copper plating and need to find out what is happening when the copper moves to the nail. My teacher said I need to describe it through a chemical equation. I am completely at a loss of how to find this out. Could you help me?

Peterdeleted
student eighth grade - Hillsborough, California


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A. Hi Peter. The copper is dissolved in the watery solution as copper ions, which are blue, and they plate out onto the nail as copper metal, which is sort of orange. I'm surprised that an 8th-grader has the chemistry vocabulary to be able to understand such a reaction as a chemical formula, but it would be approximately like this:

Fe0 + Cu++SO4-- => Cu0 + Fe++SO4- -

Copper (Cu) is more electrochemically noble than iron (Fe) so it will displace iron from the surface, i.e., cause iron metal to dissolve into the solution so it (copper) can come out as a metal. Another way to look at this is that when metals have enough electrons they appear as the familiar metallic form, but when they don't have enough electrons they appear as soluble positively charged ions dissolved in solution. When iron and copper fight over the necessary electrons to balance their positive charges, and be reduced to metal rather than being ions, copper always wins. Copper exerts this more powerful pull on electrons due to nuclear physics principles that I can't quite explain because it is beyond my grade level. Good luck!

pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey

February 22, 2009appended

Q. I have to write a lab report on this experiment...how the copper in the copper sulfate solution transfers to the iron ... why does it do this? (anything to do with electrons ... I'm in high school so a more in depth answer is fine)

Campbell Fdeleted
student - New York, New York


February 28, 2009

A. Hi, Campbell. The paper clip is zinc plated steel. Just as salt or sugar will dissolve into solution up to an equilibrium point, metals will dissolve as well. So ionized copper will be in solution from the copper sulphate, and ionized zinc will go into solution from the coating on the paper clip.

Copper is more noble than zinc, meaning that when the two metals are available in this way, the copper has a stronger affinity for becoming/staying in metallic form (i.e., to grab or hold onto its electrons so it is not oxidized). So zinc will dissolve into the solution and copper will deposit out as metal on the paper clip until the paper clip is completely covered with copper. Once it is covered with copper metal and no more zinc is exposed, the reaction is finished. To learn more, read up on the "galvanic series" and the "seawater series". Best of luck.

Regards,

pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


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Q. I am in fourth grade and I am doing the vinegar/salt with pennies copper coating a paper clip and I can't figure out what the scientific question should be for my science fair presentation.
Could it be:
Will vinegar and pennies copper coat a metal paper clip?

Madison Hdeleted
student - Ponte Vedra, Florida


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A. Hello, Madison. I think your question is excellent for a fourth grade project! Good luck!

pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey

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Q. Hi, I'm in 8th grade and I am doing a lab report but need to finish my analysis and can't figure out where the copper on the nails surface comes from?

This is urgent please respond quickly. Thank you

Julia deleted
student - Toronto, Ontario


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A. Assuming you dipped your nail into copper sulphate, the copper came from the copper sulphate, Julia. The copper is dissolved as copper ions in the blue copper sulphate, but deposits out as orange copper metal. Although copper metal is orange, copper ions are blue.

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Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


sidebar

Q. I am doing a chemistry lab, and for each reaction I need to provide a balanced equation.
The reactions are:
1. bare copper wire on a hottest part of a flame held for a few minutes.
2. a nail on a test tube of the solution copper(II) sulfate
3. solid copper (II) sulfate pentahydrate over heat
4. same as number three, but then adding few drops of water
5. calcium chloride solution and sodium carbonate solution
6. mossy zinc on a test tube with hydrochloric acid solution
Monica Sdeleted
student - Monterrey, Nl, Mexico


A. Hi, Monica. Your teacher sent me a note:

"Dear Mr. Mooney: Please just tell Monica to do her own homework!!"

Here's what I wrote back:

"I understand what you are trying to tell us, and if Monica simply pastes her homework questions here and leaves it at that, we'll do as you ask and not post any answers. But if she attempts the work, we'll try to help her over any points of confusion."

pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


December 4, 2008

Q. Hi I'm in Chemistry and one of the assignments is to figure out what you would add to a brand new shiny copper Aladdin genie lamp to make it appear as if it were a thousand years old. Obviously I would rust it, but I can't think of a creative way of rusting it, that would actually work. If I added HCl all over it would it work? What would make this lamp rust? Please help, thank you.

Jackie Odeleted
student - Salem, Massachusetts


December 2008

A. Hi, Jackie. Only the corrosion products of iron may properly be called rust. So you can't actually make a copper lamp "rust" because rust is iron oxide, and you can't make iron oxide from copper; it's not actually correct to call the corrosion products of copper 'rust'.

Something to think about is what would a thousand year old copper lamp actually look like? Would it be brown like an old penny or green like the statue of liberty? I'd go with green. I'm guessing that your teacher will expect you to try to answer that question and explain your choice.

About adding HCl, hydrochloric acid (only appropriate for high school students supervised by the science teacher). Actually HCl doesn't dissolve copper, it dissolves copper oxides. So the result is that it would make the lamp brighter if it had begun to tarnish. However, if you spritz the copper with HCl (preferably, use vinegar and salt because it's much safer) and let it dry, the copper / copper oxide that it had dissolved into the solution can't remain in solution because there will be no solution left after it evaporates. So the formerly dissolved copper would become sort of a corroded coating on the lamp. Think it all through and earn an "A". Good luck.

Regards,

pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey

August 27, 2010

Q. Hello!

I am in the tenth grade, and my chemistry class recently did a nail lab. I'm having trouble finishing my summary, and I was wondering if you could help me. We put a nail, a small spoonful of salt, some copper sulfate crystals, and water in a plastic cup. We observed this mixture for three days. I see a lot of shiny, copper-colored clumps in the cup (possibly rust), but I'm not sure what it is. My teacher wants to know what I think is happening to the nail. What I'm wondering is what really is happening? Can you help me? Thank you!

Rachel Sdeleted
Student - Nashville,Tennessee

August 30, 2010

A. Hi, Rachel.

You didn't describe anything appearing to be happening to the nail, and are asking us to guess what is happening without even the benefit of what it looks like. But what is probably happening at the core of it all is Cu++ + Fe0 => Cu0 + Fe++, with the Cu being the shiny copper color lumps you see. Good luck.

Regards,

pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


November 27, 2010

Q. I also have this question, I'm really bad at chem and don't understand this experiment, what happens to the salt/ sodium chloride in your equation? CU++ + FE0? I understand that rust is forming but I don't get how. Thank you.

Sana Rdeleted
- Chicago, Illinois, United States

November 28, 2010

A. Hi, Sana.

You say that you're "really bad at chem", so please take this as a kindly suggestion that may help, rather than as stodgy nitpicking, but proper capitalization is essential to chemistry; you can't get passable until you pay attention to capitalization. You're asking what happens when a carbon-uranium compound reacts with a fluorine-europium compound :-)

You surely meant Cu (copper) and Fe (iron) . . .

No, rust is not forming, Sana. Copper is plating out onto the iron. Dissolved copper ions (Cu++) react with iron metal (Fe0) to form copper metal (Cu0) and dissolved iron ions (Fe++). The salt / sodium chloride is an agent that helps the conductivity and corrosion but isn't really participating in the reaction very much, but to some degree there is probably a little bit of
2Na+Cl- + Fe++SO4- - <=> Na+2+SO4- - + Fe++Cl2 going on there :-)

Regards,

pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey

November 29, 2010

thumbsup2THANK YOU! I kind of got it and got it right on the homework! Thank you so much!

Sana R [returning]
- Chicago, Illinois, United States


September 15, 2011

Q. When iron nail is dipped in copper sulphate solution, the copper gets deposited on which part of nail first.

Ritu Mdeleted
student - Noida, UP, India

September 15, 2011

A. Hi, Ritu.

Please submit a sketch of where you saw the copper deposited first if you are having trouble giving it a name, and we will tell you whether it's called the point, the head, the shank, or whatever :-) Good luck.

Regards,

pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey

June 11, 2013appended

Q. When an iron nail is kept in copper sulphate solution for about 3-4 hours, which part of nail first gets reacted with the solution?

padma pdeleted
student - pondicherry, india

June 17, 2013

Hi Padma. Aren't you supposed to conduct an experiment to get this answer? We won't help you torpedo your own education, plus miss out on the fun parts. Do the experiment, make some observations, tell us what they were, and then we will be very happy to discuss it with you. Thanks.

Regards,

pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


September 17, 2011

Q. I have to do a similar experiment to the people above. In class we slid blue copper sulfate crystal into the bottom of a test tube, added piece of paper and then some water. We then added some sodium chloride, and another piece of paper and more water. Then we took a nail, removed the coating by using steel wool and added the nail. We then again added more water until it covered the nail. We then observed the thing and I'm not sure what really happened. The copper sulfate turned dark purple. The nail had reddish brown substance on it, and I'm guessing that is rust? If it is rust, was that reaction from the salt or copper sulfate?

Allan Ddeleted
- Bridgeport, Connecticut, USA

September 19, 2011

A. Hi, Allan.

Actually most of the question was answered a few times, so it's hard to know how to answer your question. I'm not sure whether you are younger and unable to understand the answers, or if you didn't read them yet.

I don't know what you are referring to with the "paper". Maybe you were checking the pH with pH paper?

The copper in copper sulphate is not in copper colored metallic form, but in an ionic form that colors the solution a deep blue. When you put an iron object into that solution, some of the iron from the surface dissolves into the solution, driving out some of the copper from the solution, which is reduced to copper metal on the surface of the iron. That turns the nail copper colored. I'm not exactly sure what is happening to the color of the solution, but some of the blue colored copper is leaving it, and some blackish iron sulphate or iron chloride is going into it.

Regards,

pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey

September 20, 2012

Q. Hi. I'm also doing an experiment of breaking up compounds.
So I had to do a lab and I was asked to write the answer for these questions if you can please help to figure it out!
*How is the method of getting Cu out of a CuSo4 solution different from separating the components of a mixture?
*State whether the copper is combined or uncombined (I don't know what to do in this part)
*(a) in the deposit on the nail
*(b) in copper sulfate solution

Perla G.
- New York


September 20, 2012

A. Hi Perla.

When you encounter questions like these, the first thing to ask yourself is: "Have I not yet figured out the answer, or do I not even understand the question?" You used the phrases "breaking up compounds" and "separating the components of a mixture" -- and that should give you some ideas; but you can also google "compounds vs. mixtures". As you study compounds vs. mixtures, the meaning of the word "combined" in this context will hopefully become apparent.

If your teacher actually wrote CuSo4, rather than CuSO4, call him or her out for it :-)
... proper capitalization is crucial in chemistry. Good luck.

Regards,

pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey

November 7, 2012

Q. Could you explain why sodium chloride causes iron nails to rust?

ANDERSON deleted
- Pappua, New Guinea

November 9, 2012

A. Hi Anderson. Please explain the experiment that you performed, and the results that you got, which seemed to indicate that sodium chloride causes iron nails to rust, and I will try to explain your findings. Or read the earlier entries on this page. Good luck.

Regards,

pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey

March 31, 2013

Q. Why does iron rusts badly if it is placed with copper plate?

Kay Adeleted
- bandar seri begawan, Brunei


April 1, 2013

A. Hi Kay. The answer is on this page already. But if you wish to view it from a different perspective, you have two different metals with two different oxidation potentials, connected with both an electrical path and an ionic path, so --

The more noble metal (copper) will steal electrons from the less noble metal (iron) that it is connected to, oxidizing them to positively charged ions which will dissolve into solution. Good luck.

Regards,

pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
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