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

A. Hi Jesse. If the steel wool is clean and free of soap, copper from the copper sulphate will deposit onto it and the steel wool will become copper colored.

The steel (iron) wool is atoms of iron metal. It is metal only because the atoms of the steel have enough electrons attached to them that the iron is able to be present as a hard metallic object. The copper sulphate is a solution which contains copper ions (the ions are lacking some necessary electrons, so they are not metallic copper atoms). The copper ions form a blue colored solution rather than a copper colored metal; without enough electrons to become copper atoms, they remain in solution.

But when you put steel wool into the copper sulphate, the steel atoms and the copper ions come in contact with each other. Copper is more noble (kingly) than the iron and is able to steal electrons from the iron. As it does, those iron atoms will become iron ions (not enough electrons to be in metallic form anymore) and will dissolve into solution. And the former copper ions, which now have enough electrons to become atoms of copper metal will do so, and form a thin skin of copper metal on the steal wool.

When all of the iron is covered with that thin skin of copper, no more iron atoms are exposed to the copper ions in the copper sulphate and the reaction stops.

A. Hi, Courtney. Actually, the chemical for copper sulphate is called copper sulphate; it is usually 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 or in diluted sulfuric acid 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!

copper sulphate rusts really quickly because when oxygen is interfered sulphate 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,

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.

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!

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,

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

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.

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

Here's what I wrote back:

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,

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,

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,

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

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,

Hi Padma. Aren't you supposed to conduct an experiment to get this answer? Don't 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,

A. Hi, Allan.

Actually most of the question was answered a few times. But maybe you are younger and unable to understand the answers?

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,

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,

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,

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,

Sorry Emily, it's too vague for me. I don't know what gas bubbles you are speaking of, nor why your procedure puts NaCl between the CuSO4 and the iron nail, or what you procedure really looks like. As a student it's important for you to distinguish between questions to which you don't know the answer vs. questions where you don't even understand the question. In the former case you are right to seek the answer, but in the latter case you must get clarity from your teacher ... and I'm not quite sure which is the case here. Good luck.

Regards,

A. Hi Srishti. A double displacement reaction is of the form
AB + CD => AD + CB

Your reaction of
CuSO4 + Fe => Cu + FeSO4 is of the form
AB + C => A + CB and there is only one displacement.

One reason the reaction doesn't continue until all Cu^2 ions have been replaced is that the iron becomes completely covered with copper in metallic form and there is no more iron exposed, so CuSO4 can't reach the iron anymore. A second issue to consider is that ferrous sulfate ⇦this on eBay or Amazon [affil links] is rather soluble in water, so it doesn't tend to precipitate in this situation. Good luck.

Regards,

A. Hi Marvin. Please google "galvanic series chart" and "seawater series chart" and you will find that pure nickel is even more noble than copper, so it looks like it should deposit on the iron nail even more readily ... but I'm quite sure that you'll discover that in fact it doesn't "immersion deposit" on iron anyway. One thing that makes science fun is that it's not dead easy and completely predictable by the simplest of rules; rather, it's always complicated enough to challenge us.

So please try it and tell us what happens ... then we can attempt to figure out why. Good luck

Regards,

A. Marvin,
I believe what you are asking for is the "electroless nickel" plating process that was first developed sometime around the 1950s.

A. Hi Pristine. Yes, it's a single displacement reaction, iron displacing copper:
Fe + CuSO₄ => Cu + FeSO₄

Assuming the intended reaction actually occurred, the 'dullness' is due to the fact that you formerly saw iron on the surface of the steel wool, but after this reaction you are now seeing copper, because the surface of the steel wool is now covered with copper.

Regards,

A. Hi Red. Your problem is probably not that you don't know the answer, but that you don't really understand the question :-)

You had a lesson, or perhaps a reading assignment, about the difference between a 'physical change' and a 'chemical change'. So google 'physical change vs. chemical change'.

A 'physical change' is one which changes the physical properties of the substance but is relatively easily reversed, such as: you can change liquid water to solid ice by cooling it, and restore it to liquid again by heating it. You can change liquid water to gaseous steam by heating it, and you can collect the steam and let it condense back to liquid.

A 'chemical change' involves making and breaking chemical bonds; it is usually quite difficult to reverse; and it generally either releases energy (such as when something burns and gives off heat) or (less commonly) absorbs energy. Although you witnessed a change in a physical property -- some of the blue copper in the solution became orange copper on the steel wool -- you can ask yourself two questions: 1. How would you go about reversing the process and getting the orange metal off of the steel wool and back into solution? It doesn't sound easy and straightforward to me. 2. Why did this color change occur? I'm not sure how far you've gotten in chemistry and if you know what reaction actually occurred. But the orange copper is copper metal whereas the blue copper is copper combined with other atoms, which means chemical bonds were made or broken.

The process gives off or absorbs heat if it is a chemical reaction, but it is probably beyond 9th grade level to design an experiment to measure a small heat change in a system like this one, so you probably need to forego that test of physical vs chemical changes. Good luck.

Regards,